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Lymph Nodes (LNs) are crucial to the immune and lymphatic systems, filtering harmful substances and regulating lymph transport. LNs consist of a lymphoid compartment (LC) that forms a porous bulk region, and a subcapsular sinus (SCS), which is a free-fluid region. Mathematical and mechanical challenges arise in understanding lymph flow dynamics. The highly vascularized lymph node connects the lymphatic and blood systems, emphasizing its essential role in maintaining the fluid balance in the body. In this work, we describe a mathematical model in a steady setting to describe the lymph transport in a lymph node. We couple the fluid flow in the SCS governed by an incompressible Stokes equation with the fluid flow in LC, described by a model obtained by means of asymptotic homogenisation technique, taking into account the multiscale nature of the node and the fluid exchange with the blood vessels inside it. We solve this model using numerical simulations and we analyze the lymph transport inside the node to elucidate its regulatory mechanisms and significance. Our results highlight the crucial role of the microstructure of the lymph node in regularising its fluid balance. These results can pave the way to a better understanding of the mechanisms underlying the lymph node's multiscale functionalities which can be significantly affected by specific physiological and pathological conditions, such as those characterising malignant tissues. [ABSTRACT FROM AUTHOR]

Objectives: The objective of our study is to evaluate the involvement of the transient receptor potential vanilloid 4 (TRPV4) in the alteration of lymphatic pumping in response to flow and determine the signaling pathways involved. Methods: We used immunofluorescence imaging and western blotting to assess TRPV4 expression in rat mesenteric lymphatic vessels. We examined inhibition of TRPV4 with HC067047, nitric oxide synthase (NOS) with L‐NNA and cyclooxygenases (COXs) with indomethacin on the contractile response of pressurized lymphatic vessels to flow changes induced by a stepwise increase in pressure gradients, and the functionality of endothelial TRPV4 channels by measuring the intracellular Ca2+ response of primary lymphatic endothelial cell cultures to the selective agonist GSK1016790A. Results: TRPV4 protein was expressed in both the endothelial and the smooth muscle layer of rat mesenteric lymphatics with high endothelial expression around the valve sites. When maintained under constant transmural pressure, most lymphatic vessels displayed a decrease in contraction frequency under conditions of flow and this effect was ablated through inhibition of NOS, COX or TRPV4. Conclusions: Our findings demonstrate a critical role for TRPV4 in the decrease in contraction frequency induced in lymphatic vessels by increases in flow rate via the production and action of nitric oxide and dilatory prostanoids. [ABSTRACT FROM AUTHOR]

Simple Summary: The ability of lymphatic vessels to achieve lymph transport by exploiting external forces acting upon the vessels or by an intrinsic pumping mechanism based on spontaneous contractions of the vessel wall is vital for the physiological drainage of interstitial fluid. The osmolarity of the microenvironment can alter the spontaneous contraction rate and therefore modify lymph formation and propulsion. Several ion channels can be involved in the molecular mechanisms underlying this response; notably, transient receptor potential channels of type V4 and V1 and volume-regulated anion channels are among them and are expressed by lymphatic vessels. In this work, we provide functional evidence that the response to hyperosmolarity and hypo-osmolarity are mediated by these three channels in a cooperative way. TRPV4 and TRPV1 channels mostly mediate both the long-term responses, while VRACs are responsible for the early increase in the contraction rate characteristic of the exposure of vessels to a hyposmolar environment. Lymphatic vessels are capable of sustaining lymph formation and propulsion via an intrinsic mechanism based on the spontaneous contraction of the lymphatic muscle in the wall of lymphatic collectors. Exposure to a hyper- or hypo-osmolar environment can deeply affect the intrinsic contraction rate and therefore alter lymph flow. In this work, we aimed at defining the putative receptors underlying such a response. Functional experiments were conducted in ex vivo rat diaphragmatic specimens containing spontaneously contracting lymphatic vessels that were exposed to either hyper- or hypo-osmolar solutions. Lymphatics were challenged with blockers to TRPV4, TRPV1, and VRAC channels, known to respond to changes in osmolarity and/or cell swelling and expressed by lymphatic vessels. Results show that the normal response to a hyperosmolar environment is a steady decrease in the contraction rate and lymph flow and can be prevented by blocking TRPV1 channels with capsazepine. The response to a hyposmolar environment consists of an early phase of an increase in the contraction rate, followed by a decrease. The early phase is abolished by blocking VRACs with DCPIB, while blocking TRPV4 mainly resulted in a delay of the early response. Overall, our data suggest that the cooperation of the three channels can shape the response of lymphatic vessels in terms of contraction frequency and lymph flow, with a prominent role of TRPV1 and VRACs. [ABSTRACT FROM AUTHOR]

Animal models of diseases, particularly mice, are considered to be the cornerstone for translational research in immunology. The aim of the present study is to model the geometry and analyze the network structure of the murine lymphatic system (LS). The algorithm for building the graph model of the LS makes use of anatomical data. To identify the edge directions of the graph model, a mass balance approach to lymph dynamics based on the Hagen–Poiseuille equation is applied. It is the first study in which a geometric model of the murine LS has been developed and characterized in terms of its structural organization and the lymph transfer function. Our study meets the demand for quantitative mechanistic approaches in the growing field of immunoengineering to utilize or exploit the lymphatic system for immunotherapy. [ABSTRACT FROM AUTHOR]

A large number of neutrophils infiltrate the lymph node (LN) within 4 h after Staphylococcus aureus skin infection (4 h postinfection [hpi]) and prevent systemic S. aureus dissemination. It is not clear how infection in the skin can remotely and effectively recruit neutrophils to the LN. Here, we found that lymphatic vessel occlusion substantially reduced neutrophil recruitment to the LN. Lymphatic vessels effectively transported bacteria and proinflammatory chemokines (i.e., Chemokine [C-X-C motif] motif 1 [CXCL1] and CXCL2) to the LN. However, in the absence of lymph flow, S. aureus alone in the LN was insufficient to recruit neutrophils to the LN at 4 hpi. Instead, lymph flow facilitated the earliest neutrophil recruitment to the LN by delivering chemokines (i.e., CXCL1, CXCL2) from the site of infection. Lymphatic dysfunction is often found during inflammation. During oxazolone (OX)-induced skin inflammation, CXCL1/2 in the LN was reduced after infection. The interrupted LN conduits further disrupted the flow of lymph and impeded its communication with high endothelial venules (HEVs), resulting in impaired neutrophil migration. The impaired neutrophil interaction with bacteria contributed to persistent infection in the LN. Our studies showed that both the flow of lymph from lymphatic vessels to the LN and the distribution of lymph in the LN are critical to ensure optimal neutrophil migration and timely innate immune protection in S. aureus infection. [ABSTRACT FROM AUTHOR]

Purpose: To evaluate correlation of single photon emission computed tomography-computed tomography (SPECT-CT) data on lymph flow (LF) from oral tongue cancer (OC) and the topography of lymph nodes (LN) metastases; to determine the clinical value of lymph flow guided radiotherapy (LFGRT). Materials and Methods: SPECT-CT visualization of LF from the OC lesions was performed after peritumoral injection of 99mTc-phytate in 26 primary patients with clinical stage cT1-2N0M0 disease. We determined the individual drainage (unilateral/bilateral) from the tumor, and localization of sentinel LNs according to the neck levels. Metastases in LNs were verified with histology and a 2-year follow-up. Results: SPECT-CT detected bilateral LF in 10 (38.5%) of 26 patients; in 16 (61.5%) cases the drainage was unilateral. Histology revealed LNs metastases in three cases; regional recurrences were diagnosed in other four patients. In all seven observations metastases were located at the same site and level as the sentinel LNs. In eight (30.8%) of 26 patients sentinel LNs were visualized unilaterally at levels Ib-IIa; in five cases, unilaterally at levels I-IIa-III. In these patients, LFGRT demonstrated 59%-70% reduction of irradiated volume, and 26%-42% and 51%-70% decrease of the mean dose to the spinal cord and the contralateral parotid gland. In patients with a bilateral drainage the reduction of doses absorbed by the spinal cord and contralateral parotid gland was 19% and 6%, respectively. Conclusion: Localization of sentinel LNs determined by SPECT-CT corresponds to the localization of metastatic LNs in terms of side and levels. [ABSTRACT FROM AUTHOR]

Surgical intervention and subsequent wound healing process are known to induce neo-lymphangiogenesis, but few studies have been reported to utilize this mechanism for lymphedema treatment. The aim of this study was to evaluate feasibility of subdermal dissection for neo-lymphangiogenesis induction (SDN) to treat lower extremity lymphedema (LEL). Medical records of secondary LEL patients who had undergone ICG lymphography and SDN procedure were reviewed. SDN was performed by dissecting fat tissues just below the dermis from the most proximal area showing dermal backflow through abdominal-to-axillary lymphatic pathways. Perioperative lymphedematous conditions were evaluated with lymphedema quality of life score (LeQOLiS) and LEL index. Seventeen female patients were included. SDN could be performed in 10 minutes on average without postoperative complication. Postoperative ICG lymphography showed new lymphatic pathways in 6 (35.3%) cases. Postoperative LeQOLiS ranged from 9 to 66, which was statistically lower than preoperative LeQOLiS (32.9 ± 19.2 vs. 36.6 ± 19.3, p = 0.048), whereas there was no statistically significant difference between pre- and post-operative LEL index (275.2 ± 23.3 vs. 270.5 ± 20.8, P = 0.073). Subdermal dissection, although its probability is not high, has a potential to induce neo-lymphangiogenesis. Further studies are required to improve and demonstrate efficacy of the procedure for new lymphatic pathway creation. [ABSTRACT FROM AUTHOR]

Background and Purpose: Doxorubicin (DOX) is a risk factor for arm lymphedema in breast cancer patients. We reported that DOX opens ryanodine receptors (RYRs) to enact "calcium leak," which disrupts the rhythmic contractions of lymph vessels (LVs) to attenuate lymph flow. Here, we evaluated whether dantrolene, a clinically available RYR1 subtype antagonist, prevents the detrimental effects of DOX on lymphatic function. Experimental Approach: Isolated rat mesenteric LVs were cannulated, pressurized (4–5 mm Hg) and equilibrated in physiological salt solution and Fura-2AM. Video microscopy recorded changes in diameter and Fura-2AM fluorescence tracked cytosolic free calcium ([Ca2+i]). High-speed in vivo microscopy assessed mesenteric lymph flow in anesthetized rats. Flow cytometry evaluated RYR1 expression in freshly isolated mesenteric lymphatic muscle cells (LMCs). Key Results: DOX (10 μmol/L) increased resting [Ca2+i] by 17.5 ± 3.7% in isolated LVs (n = 11). The rise in [Ca2+i] was prevented by dantrolene (3 μmol/L; n = 10). A single rapid infusion of DOX (10 mg/kg i.v.) reduced positive volumetric lymph flow to 29.7 ± 10.8% (n = 7) of baseline in mesenteric LVs in vivo. In contrast, flow in LVs superfused with dantrolene (10 μmol/L) only decreased to 76.3 ± 14.0% (n = 7) of baseline in response to DOX infusion. Subsequently, expression of the RYR1 subtype protein as the presumed dantrolene binding site was confirm in isolated mesenteric LMCs by flow cytometry. Conclusion and Implications: We conclude that dantrolene attenuates the acute impairment of lymph flow by DOX and suggest that its prophylactic use in patients subjected to DOX chemotherapy may lower lymphedema risk. [ABSTRACT FROM AUTHOR]

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The lymphatic system drains and propels lymph by extrinsic and intrinsic mechanisms. Intrinsic propulsion depends upon spontaneous rhythmic contractions of lymphatic muscles in the vessel walls and is critically affected by changes in the surrounding tissue like osmolarity and temperature. Lymphatics of the diaphragm display a steep change in contraction frequency in response to changes in temperature, and this, in turn, affects lymph flow. In the present work, we demonstrated in an ex vivo diaphragmatic tissue rat model that diaphragmatic lymphatics express transient receptor potential channels of the vanilloid 4 subfamily (TRPV4) and that their blockade by both the nonselective antagonist Ruthenium Red and the selective antagonist HC-067047 abolished the response of lymphatics to temperature changes. Moreover, the selective activation of TRPV4 channels by means of GSK1016790A mirrored the behavior of vessels exposed to increasing temperatures, pointing out the critical role played by these channels in sensing the temperature of the lymphatic vessels’ environment and thus inducing a change in contraction frequency and lymph flow. NEW & NOTEWORTHY The present work addresses the putative receptor system that enables diaphragmatic lymphatics to change intrinsic contraction frequency and thus lymph flow according to the changes in temperature of the surrounding environment, showing that this role can be sustained by TRPV4 channels alone. [ABSTRACT FROM AUTHOR]

Initial lymphatic vessels are made up of overlapped endothelial cells that act as unidirectional valves enabling one-way drainage of tissue fluid into the lumen of the initial lymphatics when there is a favourable pressure gradient. Initial lymphatics subsequently drain this fluid into the collecting lymphatics. This paper describes a computational model for a network of passive rat mesenteric lymphatic vessels with sparse secondary valves. The network was simulated with the secondary valves both operational and non-operational. The effects on the cycle-mean outflow-rate from the network of both inflammation and the resistance of the surrounding interstitium were considered. The cycle-mean outflow-rate is sensitive to vessel stiffness. If the influence of primary-valve resistance is reduced relative to that of interstitial resistance and intravascular resistance, there is no absolute advantage of extrinsic pumping, since maximum outflow-rate occurs when vessels are rigid. However, there is relative advantage, in that the outflow-rate at intermediate stiffness is higher with the secondary valves functioning than when they are deactivated. If primary-valve resistance dominates, then extrinsic pumping of non-rigid vessels provides absolute advantage. The nonlinear relation between pressure drop and flow-rate of the endothelial primary valves, combined with downstream compliance and pulsatile external pressure, constitutes a separate mechanism of pumping. By enabling the consideration of interactions between multiple phenomena (primary valves, secondary valves, a real network geometry with multiple branches, deformable vessel walls, interstitial resistance and external pressures), the model offers a perspective for delineating physiological phenomena that have not yet been fully linked to the biomechanics of fluid flow through initial lymphatic networks. [ABSTRACT FROM AUTHOR]

Recently, the presence of lymphatics has been demonstrated and characterized in the dura mater, which is in contrast to the well-accepted view indicating the lack of a classical lymphatic drainage system of the central nervous system (CNS). Moreover, the role of meningeal lymphatics in the pathogenesis of Alzheimer's disease and multiple sclerosis was suggested. However, the possible regulators of the developmental program and function of meningeal lymphatics remain unclear. Here, we aimed at characterizing the lymph flow dependence of the developmental program and function of the meningeal lymphatics. First, we demonstrated that lymphatics present in the dura mater are involved in the uptake and transport of macromolecules from the CNS. Meningeal lymphatics develop during the postnatal period which process involves the maturation of the vessels. The formation of mature meningeal lymphatics coincides with the increase of the drainage of macromolecules from the CNS to the deep cervical lymph nodes. Importantly, the structural remodeling and maturation of meningeal lymphatics is impaired in Plc γ 2 −/− mice with reduced lymph flow. Furthermore, macromolecule uptake and transport by the meningeal lymphatics are also affected in Plc γ 2 −/− mice. Collectively, lymph flow-induced mechanical forces are required for the postnatal formation of mature and functional meningeal lymphatic vessels. Defining lymph flow-dependence of the development and function of meningeal lymphatics may lead to better understanding of the pathogenesis of neurological diseases including Alzheimer's disease and multiple sclerosis. [ABSTRACT FROM AUTHOR]

A model of lymph flow in the human lymphatic system in the quasi-one-dimensional approach has been created and investigated under different conditions. The model includes an implementation of contractions and valve influence on lymph flow. We consider contractions of lymphatic vessels and their influence on resulting flow in the whole network of lymphatic vessels and lymph nodes. We have investigated flow with zero pressure gradient and have found parameters, which influence the efficiency of contractions most significantly. [ABSTRACT FROM AUTHOR]

Adaptive immune responses develop in secondary lymphoid organs such as lymph nodes (LNs) in a well-coordinated series of interactions between migrating immune cells and resident stromal cells. Although many processes that occur in LNs are well understood from an immunological point of view, our understanding of the fundamental organization and mechanisms that drive these processes is still incomplete. The aim of systems biology approaches is to unravel the complexity of biological systems and describe emergent properties that arise from interactions between individual constituents of the system. The immune system is greater than the sum of its parts, as is the case with any sufficiently complex system. Here, we review recent work and developments of computational LN models with focus on the structure and organization of the stromal cells. We explore various mathematical studies of intranodal T cell motility and migration, their interactions with the LN-resident stromal cells, and computational models of functional chemokine gradient fields and lymph flow dynamics. Lastly, we discuss briefly the importance of hybrid and multi-scale modeling approaches in immunology and the technical challenges involved. [ABSTRACT FROM AUTHOR]

The paper describes the extension of a previously developed model of pressure-dependent contraction rate to the case of multiple lymphangions. Mechanical factors are key modulators of active lymphatic pumping. As part of the evolution of our lumped-parameter model to match experimental findings, we have designed an algorithm whereby the time until the next contraction depends on lymphangion transmural pressure in the contraction just completed. The functional dependence of frequency on pressure is quantitatively matched to isobaric contraction experiments on isolated lymphatic segments. When each of several lymphangions is given this ability, a scheme for their coordination must be instituted to match the observed synchronization. Accordingly, and in line with an experiment on an isolated lymphatic vessel segment in which we measured contraction sequence and conduction delay, we took the fundamental principle to be that local timing can be overridden by signals to initiate contraction that start in adjacent lymphangions, conducted with a short delay. The scheme leads to retrograde conduction when the lymphangion chain is pumping against an adverse pressure difference, but antegrade conduction when contractions occur with no or a favourable pressure difference. Abolition of these conducted signals leads to chaotic variation of cycle-mean flow-rate from the chain, diastolic duration in each lymphangion, and inter-lymphangion delays. Chaotic rhythm is also seen under other circumstances. Because the model responds to increasing adverse pressure difference by increasing the repetition rate of contractions, it maintains time-average output flow-rate better than one with fixed repetition rate. [ABSTRACT FROM AUTHOR]

The lymphatic system contributes to body homeostasis by clearing fluid, lipids, plasma proteins and immune cells from the interstitial space. Many studies have been performed to understand lymphatic function under normal conditions and during disease. Nevertheless, a further improvement in quantification of lymphatic behavior is needed. Here, we present advanced bright‐field microscopy for in vivo imaging of lymph vessels (LVs) and automated quantification of lymphatic function at a temporal resolution of 2 milliseconds. Full frame videos were compressed and recorded continuously at up to 540 frames per second. A new edge detection algorithm was used to monitor vessel diameter changes across multiple cross sections, while individual cells in the LVs were tracked to estimate flow velocity. The system performance initially was verified in vitro using 6‐ and 10‐μm microspheres as cell phantoms on slides and in 90‐μm diameter tubes at flow velocities up to 4 cm/second. Using an in vivo rat model, we explored the mechanisms of lymphedema after surgical lymphadenectomy of the mesentery. The system revealed reductions of mesenteric LV contraction and flow rate. Thus, the described imaging system may be applicable to the study of lymphatic behavior during therapeutic and surgical interventions, and potentially during lymphatic system diseases. [ABSTRACT FROM AUTHOR]

The lymphatic system aids in osmoregulation through tissue fluid transport, but is also designed to support communication between cells of the innate and adaptive immune systems. During inflammation, changes within the lymphatics can result in an altered response to infection. Neutrophils have been described as one key cell type that facilitates antigen capture and presentation within the lymphatic system, enabling an effective adaptive immune response. Disruption of neutrophil recruitment during inflammation, due to alterations in lymphatics, is a growing area of study due to their key role in infection resolution. In this review, we discuss the currently known methods by which neutrophils are recruited to the lymphatic system and what subsequent effects they have on resident and recruited cells within the lymph vessels and nodes. We also discuss the changes in neutrophil activation and recruitment during chronic inflammatory diseases and their relationship to lymphatic dysfunction. [ABSTRACT FROM AUTHOR]

Key points For therapeutic antibodies, total tissue concentrations are frequently reported as a lump sum measure of the antibody in residual plasma, interstitial fluid and cells. In terms of correlating antibody exposure to a therapeutic effect, however, interstitial pharmacokinetics might be more relevant., In the present study, we collected total tissue and interstitial antibody biodistribution data in mice and assessed the composition of tissue samples aiming to correct total tissue measurements for plasma and cellular content., All data and parameters were integrated into a refined physiologically-based pharmacokinetic model for monoclonal antibodies to enable the tissue-specific description of antibody pharmacokinetics in the interstitial space., We found that antibody interstitial concentrations are highly tissue-specific and dependent on the underlying capillary structure but, in several tissues, they reach relatively high interstitial concentrations, contradicting the still-prevailing view that both the distribution to tissues and the interstitial concentrations for antibodies are generally low., Abstract For most therapeutic antibodies, the interstitium is the target space. Although experimental methods for measuring antibody pharmacokinetics (PK) in this space are not well established, thus making quantitative assessment difficult, the interstitial antibody concentration is assumed to be low. In the present study, we combined direct quantification of antibodies in the interstitial fluid with a physiologically-based PK (PBPK) modelling approach, with the aim of better describing the PK of monoclonal antibodies in the interstitial space of different tissues. We isolated interstitial fluid by tissue centrifugation and conducted an antibody biodistribution study in mice, measuring total tissue and interstitial concentrations in selected tissues. Residual plasma, interstitial volumes and lymph flows, which are important PBPK model parameters, were assessed in vivo. We could thereby refine the PBPK modelling of monoclonal antibodies, better interpret antibody biodistribution data and more accurately predict their PK in the different tissue spaces. Our results indicate that, in tissues with discontinuous capillaries (liver and spleen), interstitial concentrations are reflected by the plasma concentration. In tissues with continuous capillaries (e.g. skin and muscle), ∼50-60% of the plasma concentration is found in the interstitial space. In the brain and kidney, on the other hand, antibodies are restricted to the vascular space. Our data may significantly impact the interpretation of biodistribution data of monoclonal antibodies and might be important when relating measured concentrations to a therapeutic effect. By contrast to the view that the antibody distribution to the interstitial space is limited, using direct measurements and model-based data interpretation, we show that high antibody interstitial concentrations are reached in most tissues. [ABSTRACT FROM AUTHOR]

Lymph drainage and propulsion are sustained by an extrinsic mechanism, based on mechanical forces acting from the surrounding tissues against the wall of lymphatic vessels, and by an intrinsic mechanism attributable to active spontaneous contractions of the lymphatic vessel muscle. Despite being heterogeneous, the mechanisms underlying the generation of spontaneous contractions share a common biochemical nature and are thus modulated by temperature. In this study, we challenged excised tissues from rat diaphragm and hindpaw, endowed with spontaneously contracting lymphatic vessels, to temperatures from 24°C (hindpaw) or 33°C (diaphragmatic vessels) to 40°C while measuring lymphatic contraction frequency (fc) and amplitude. Both vessel populations displayed a sigmoidal relationship between fc and temperature, each centered around the average temperature of surrounding tissue (36.7 diaphragmatic and 32.1 hindpaw lymphatics). Although the slope factor of the sigmoidal fit to the fc change of hindpaw vessels was 2.3°C·cycles-1·min-1, a value within the normal range displayed by simple biochemical reactions, the slope factor of the diaphragmatic lymphatics was 0.62°C·cycles-1·min-1, suggesting the added involvement of temperature-sensing mechanisms. Lymph flow calculated as a function of temperature confirmed the relationship observed on fc data alone and showed that none of the two lymphatic vessel populations would be able to adapt to the optimal working temperature of the other tissue district. This poses a novel question whether lymphatic vessels might not adapt their function to accommodate the change if exposed to a surrounding temperature, which is different from their normal condition. [ABSTRACT FROM AUTHOR]

Lymphatic vessels are important for maintenance of tissue fluid homeostasis and afferent antigen transport. In chronic inflammation, lymphangiogenesis takes place and is characterized by lymphatic endothelial cell proliferation and lymphatic hyperplasia. Vascular endothelial growth factor C (VEGFC) is the main known lymphangiogenic growth factor, and its expression is increased in periodontitis, a common chronic infectious disease that results in tissue destruction and alveolar bone loss. The role of lymphangiogenesis during development of periodontitis is unknown. Here, we test if transgenic overexpression of epithelial VEGFC in a murine model is followed by hyperplasia of lymphatic vessels in oral mucosa and if the lymphatic drainage capacity is altered. We also test if lymphatic hyperplasia protects against periodontal disease development. Transgenic keratin 14 (K14)-VEGFC mice had significant hyperplasia of lymphatics in oral mucosa, including gingiva, without changes in blood vessel vasculature. The basal lymph flow was normal but slightly lower than in wild-type mice when oral mucosa was challenged with lipopolysaccharide from Porphyromonas gingivalis. Under normal conditions, K14-VEGFC mice exhibited an increased number of neutrophils in gingiva, demonstrated enhanced phagocyte recruitment in the cervical lymph nodes, and had more alveolar bone when compared with their wild-type littermates. After induction of periodontitis, no strain differences were observed in the periodontal tissues with respect to granulocyte recruitment, bone resorption, angiogenesis, cytokines, and bone-related protein expressions or in draining lymph node immune cell proportions and vascularization. We conclude that overexpression of VEGFC results in hyperplastic lymphatics, which do not enhance lymphatic drainage capacity but facilitate phagocyte transport to draining lymph nodes. Hyperplasia of lymphatics does not protect against development of ligature-induced periodontitis. [ABSTRACT FROM AUTHOR]

Purpose: The treatment of splenic flexural colon cancer is not standardized because the lymphatic drainage is variable. The aim of this study is to evaluate the lymph flow at the splenic flexure. Methods: From July 2013 to January 2016, consecutive patients of the splenic flexural colon cancer with a preoperative diagnosis of N0 who underwent laparoscopic surgery were enrolled. Primary outcome is frequency of the direction of lymph flow from splenic flexure. We injected indocyanine green (2.5 mg) into the submucosal layer around the tumor and observed lymph flow using the laparoscopic near-infrared camera system in 30 min after injection. Results: Thirty-one patients were enrolled in this study. The lymph flow was visualized in 31 patients (100 %) without any complications. No case exhibited lymph flow in both the left colic artery (LCA) and left branch of the middle colic artery (lt-MCA) areas. There were 19 cases (61.3 %) with lymph flow directed to the area of the root of the inferior mesenteric vein (IMV), regardless of the presence of the left accessory aberrant colic artery. Lymph node metastases were observed in six cases (19.4 %), and all of the involved lymph nodes existed in lymph flow areas determined by real-time indocyanine green fluorescence imaging. Conclusions: The findings of the lymph flow pattern of splenic flexure suggest that lymph node dissection at the root of the IMV area is important, and it may be not necessary to ligate both the lt-MCA and LCA, at least in cases without widespread lymph node metastases. [ABSTRACT FROM AUTHOR]

In this study, we discuss critical issues in modelling the structure and function of lymph nodes (LNs), with emphasis on how LN physiology is related to its multi-scale structural organization. In addition to macroscopic domains such as B-cell follicles and the T cell zone, there are vascular networks which play a key role in the delivery of information to the inner parts of the LN, i.e., the conduit and blood microvascular networks. We propose object-oriented computational algorithms to model the 3D geometry of the fibroblastic reticular cell (FRC) network and the microvasculature. Assuming that a conduit cylinder is densely packed with collagen fibers, the computational flow study predicted that the diffusion should be a dominating process in mass transport than convective flow. The geometry models are used to analyze the lymph flow properties through the conduit network in unperturbed- and damaged states of the LN. The analysis predicts that elimination of up to 60%-90% of edges is required to stop the lymph flux. This result suggests a high degree of functional robustness of the network. [ABSTRACT FROM AUTHOR]

From various sources, we know that the science of spermatologii studied at various farm animals. The composition and properties of surface plasma membrane glycolipids determine mitotic phase cell activity and cell division. Demonstrated their exceptional role in cell-cell interactions: in the phenomena of «recognition» of cells to each other, adhesion, differentiation, growth, proliferation, contact inhibition of growth. In this article, we were examined lymph, lymph and blood composition, such as the volume of blood plasma in rams against the backdrop of one of the oldest forms of non-specific defense response - inflammation caused by surgical injury. Experiments were carried out on 14 rams Altai Merino. After a clinical examination of the animals, quickly create lymph venous anastomosis between the thoracic duct and jugular vein on the previously developed modifications N. Myrzakhanova, 1980. To prevent the lymph and blood clotting heparin was injected intravenously. A sample of the lymph and blood for analysis were taken from the thoracic duct and jugular vein. Elactica Kastrati morning before and after the conference. Analysis of morphological composition of blood and bodices, and total protein was carried out by conventional methods in hematology and hematocrit using microcapillary. Studies have shown that after elastica Kastrati observed very excited animal. There was an increase in heart rate of 66 to 81 beats per minute and respiration of 16 to 28 breaths per minute. Increased body temperature to the upper limit of normal (before 39.90) and inhibition of motor-evacuation activity of the rumen from 3.5 to 1.2 beats per minute. These changes most evident the first 1-2 hours (Р<0, 01-0,001), and then restored to the original values. Dynamics of white blood cells in the lymph and blood in this phase were determined not only the formation and release them in the lymph and circulatory changes depended on. This is evidenced by the decline in the value of lymph flow and hematocrit. Thus, reduction in the number of blood leukocytes Incoming defined reduction in lymph circulation on the one hand and an increase of the plasma volume with the other. Physiological assessment of the above leads to the conclusion that post-traumatic reaction at elastica Kastrati proceed fully and relatively easily transferred animals. [ABSTRACT FROM AUTHOR]

Shear-dependent inhibition of lymphatic thoracic duct (TD) contractility is principally mediated by nitric oxide (NO). Endothelial dysfunction and poor NO bioavailability are hallmarks of vasculature dysfunction in states of insulin resistance and metabolic syndrome (MetSyn). We tested the hypothesis that flow-dependent regulation of lymphatic contractility is impaired under conditions of MetSyn. We utilized a 7-wk high-fructose-fed male Sprague-Dawley rat model of MetSyn and determined the stretch- and flow-dependent contractile responses in an isobaric ex vivo TD preparation. TD diameters were tracked and contractile parameters were determined in response to different transmural pressures, imposed flow, exogenous NO stimulation by S-nitro-N-acetylpenicillamine (SNAP), and inhibition of NO synthase (NOS) by L-nitro-arginine methyl ester (L-NAME) and the reactive oxygen species (ROS) scavenging molecule 4-hydroxytempo (tempol). Expression of endothelial NO synthase (eNOS) in TD was determined using Western blot. Approximately 25% of the normal flow-mediated inhibition of contraction frequency was lost in TDs isolated from MetSyn rats despite a comparable SNAP response. Inhibition of NOS with L-NAME abolished the differences in the shear-dependent contraction frequency regulation between control and MetSyn TDs, whereas tempol did not restore the flow responses in MetSyn TDs. We found a significant reduction in eNOS expression in MetSyn TDs suggesting that diminished NO production is partially responsible for impaired flow response. Thus our data provide the first evidence that MetSyn conditions diminish eNOS expression in TD endothelium, thereby affecting the flow-mediated changes in TD lymphatic function. [ABSTRACT FROM AUTHOR]

Objective This study investigated the roles of the H1 and H2 histamine receptors, NO synthase, and s GC cyclase in histamine-induced modulation of rat mesenteric collecting lymphatic pumping. Methods Isolated rat mesenteric collecting lymphatics were treated with 1- to 100- μM histamine. Histamine receptors were blocked with either the H1 antagonist mepyramine or the H2 antagonist cimetidine. The role of NO/s GC signaling was tested using the arginine analog l- NAME, the s GC inhibitor ODQ, and SNP as a positive control. Results Histamine applied at 100 μM decreased tone and CF of isolated rat mesenteric collecting lymphatics. Pharmacologic blockade of either H1 or H2 histamine receptors significantly inhibited the response to histamine. Pretreatment with ODQ, but not l- NAME, completely inhibited the histamine-induced decrease in tone. ODQ pretreatment also significantly inhibited SNP-induced lymphatic relaxation. Conclusions H1 and H2 histamine receptors are both involved in histamine-induced relaxation of rat mesenteric collecting lymphatics. NO synthesis does not appear to contribute to the histamine-induced response. However, s GC is critical for the histamine-induced decrease in tone and contributes to the drop in CF. [ABSTRACT FROM AUTHOR]

Lymph flow is the primary mechanism for returning interstitial fluid to the blood circulation. Currently, the adaptive response of lymphatic vessels to mesenteric venous hypertension is not known. This study sought to determine the functional responses of postnodal mesenteric lymphatic vessels. We surgically occluded bovine mesenteric veins to create mesenteric venous hypertension to elevate mesenteric lymph flow. Three days after surgery, postnodal mesenteric lymphatic vessels from mesenteric venous hypertension (MVH; n = 7) and sham surgery (Sham; n = 6) group animals were evaluated and compared. Contraction frequency (MVH: 2.98 ± 0.75 min1; Sham: 5.42 ± 0.81 min-1) and fractional pump flow (MVH: 1.14 ± 0.30 min1; Sham: 2.39 ± 0.32 min-1) were significantly lower in the venous occlusion group. These results indicate that postnodal mesenteric lymphatic vessels adapt to mesenteric venous hypertension by reducing intrinsic contractile activity. [ABSTRACT FROM AUTHOR]

We studied contractile function of isolated mesenteric lymph nodes in rats with toxic hepatitis. We observed suppression of spontaneous and stimulated contractile activity of mesenteric lymph nodes and changes in biochemical composition of the lymph. We propose a method of correction of these dysfunctions with antioxidant α-tocopherol and Selen-Active. [ABSTRACT FROM AUTHOR]

Abnormalities of the lymphatic circulation are well recognized in patients with congenital heart defects. However, it is not known how the associated abnormal blood flow patterns, such as increased pulmonary blood flow (PBF), might affect pulmonary lymphatic function and structure. Using well-established ovine models of acute and chronic increases in PBF, we cannulated the efferent lymphatic duct of the caudal mediastinal node and collected and analyzed lymph effluent from the lungs of lambs with acutely increased PBF (n = 6), chronically increased PBF (n = 6), and age-matched normal lambs (n = 8). When normalized to PBF, we found that lymph flow was unchanged following acute increases in PBF but decreased following chronic increases in PBF. The lymph: plasma protein ratio decreased with both acute and chronic increases in PBF. Lymph bioavailable nitric oxide increased following acute increases in PBF but decreased following chronic increases in PBF. In addition, we found perturbations in the transit kinetics of contrast material through the pleural lymphatics of lambs with chronic increases in PBF. Finally, there were structural changes in the pulmonary lymphatic system in lambs with chronic increases in PBF: lymphatics from these lambs were larger and more dilated, and there were alterations in the expression of vascular endothelial growth factor-C, lymphatic vessel endothelial hyaluronan receptor-1, and Angiopoietin-2, proteins known to be important for lymphatic growth, development, and remodeling. Taken together these data suggest that chronic increases in PBF lead to both functional and structural aberrations of lung lymphatics. These findings have important therapeutic implications that warrant further study. [ABSTRACT FROM AUTHOR]

Microscopic lymphatics produce nitric oxide (NO) during contraction as flow shear activates the endothelial cells. The valve leaflets and bulbous valve housing contain a large amount of endothelial nitric oxide synthase (eNOS) due both to many endothelial cells and increased expression of eNOS. Direct NO measurements indicate the valve area has a 30-50% higher NO concentration ([NO]) than tubular regions although both regions generate equivalent relative increases in [NO] with each contraction. We hypothesize that 1) the greater eNOS and [NO] of the bulb region would have greater effects to lower pumping activity of the overall lymphatic than occurs in tubular regions and 2), the elevated [NO] in the bulb region may be because of high NO production in the valve leaflets that diffuses to the wall of the bulb. Measurement of [NO] with a micropipette inside the lymphatic bulb revealed the valve leaflets generate ~50% larger [NO] than the bulb wall in the in vivo rat mesenteric lymphatics. The valves add NO to the lymph that quickly diffuses to the bulb wall. Bradykinin locally released iontophoretically from a micropipette on both bulbs and tubes increased the [NO] in a dose-dependent manner up to ~50%, demonstrating agonist activation of the NO pathway. However, pumping output determined by contraction frequency and stroke volume decreased much more for the bulb than tubular areas in response to the bradykinin. In effect, NO generation by the bulb area and its valves limits the pumped flow of the total lymphatic by lowering frequency and stroke volume of individual contractions. [ABSTRACT FROM AUTHOR]

Miller NE, Michel CC, Nanjee MN, Olszewski WL, Miller IP, Hazell M, Olivecrona G, Sutton P, Humphreys SM, Frayn KN. Secretion of adipokines by human adipose tissue in vivo: partitioning between capillary and lymphatic transport. Am J Physiol Endocrinol Metab 301: E659-E667, 2011. First published July 12, 2011; doi: 10.1152/ajpendo.00058.2011.--Peptides secreted by adipose tis sue (adipokines) may enter blood via capillaries or lymph. The relative importance of these pathways for a given adipokine might influence its biological effects. Because this has not been studied in any species, we measured the concentrations of seven adipokines and eight nonsecreted proteins in afferent peripheral lymph and venous plasma from 12 healthy men. Data for nonsecreted proteins were used to derive indices of microvascular permeability, which in conjunction with the molecular radii of the adipokines were used to estimate the amounts leaving the tissue via capillaries. Transport rates via lymph were estimated from the lymph adipokine concentrations and lymph flow rates and total transport (secretion) as the sum of this and capillary transport. Concentrations of nonsecreted proteins were always lower in lymph than in plasma. With the exception of adiponectin, adipokine concentrations were always higher in lymph (P < 0.01). Leptin and MCP-1 were secreted at the highest rates (means: 43 μg/h or 2.7 nmol/h and 32 μg/h or 2.4 nmol/h, respectively). IL-6 and MCP-1 secretion rates varied greatly between subjects. The proportion of an adipokine transported via lymph was directly related to its molecular radius (r5 +0.94, P = 0.025, n 6), increasing from 14 to 100% as the radius increased from 1.18 (IL-8) to 3.24 nm (TNFa). We conclude that the lymph/capillary partitioning of adipokines is a function of molecular size, which may affect both their regional and systemic effects in vivo. This finding may have implications for the physiology of peptides secreted by other tissues. [ABSTRACT FROM AUTHOR]

Guar gum has a well-recognized hypolipidemic effect. This effect is thought to be due to the physicochemical properties of guar gum, which may cause changes in adsorption of lipids or the viscosity of the intestinal contents. Guar gum is a non-specific absorption inhibitor of any type of lipid-soluble compound. Permanent lymph duct cannulation was performed on rats to investigate the effects of dietary guar gum on lymph flow and lipid transport. Rats fed a 5% guar gum diet were compared with those fed a 5% cellulose diet, and lymph was collected after feeding. The water-holding capacity (WHC), settling volume in water (SV), and viscosity of guar gum were compared with those of cellulose. Rats fed with the guar gum diet had significantly lower lymph flow and lymphatic lipid transport than did rats fed with the cellulose diet. The WHC, SV, and viscosity of guar gum were significantly higher than those of cellulose. We propose that dietary guar gum reduces lymph flow and thereby diminishes lipid transport by means of its physicochemical properties related to water behavior in the intestine. [ABSTRACT FROM AUTHOR]

This minireview summarizes an oral presentation given at the National Institute of Diabetes and Digestive and Kidney Diseases National Institutes of Health workshop 'Lymphatics in the Digestive System: Physiology, Health, and Disease' in Bethesda, Maryland on November 3-4, 2009. The concepts of extrinsic and intrinsic pumps, as well as intrinsic and extrinsic flows, are discussed in relation to the lymph transport in mesenteric lymphatic vessels. Age-related alterations in the structure and regulatory mechanisms of lymph flow in mesenteric lymphatic vessels may provide the basis for their diminished ability to work during the periods of increased functional loads in them. The recent development of modern experimental tools provides the opportunity to extend the knowledge on lymph transport function of lymphatic vessels that is absolutely necessary to maintain fluid and macromolecular homeostasis and to provide a transportation route for lipids adsorbed in gut and to immune cells. [ABSTRACT FROM AUTHOR]

Abstract: The lymphatic system is composed of a dense network of lymphatic vessels, which are critical components of physiological interstitial fluid transport. These vessels possess intrinsic contractile properties providing the driving force for the fluid to be drained away from the tissues and propelled, as lymph, back into the bloodstream. Lymphatic pumping is also important to carry immune cells, bacteria, macromolecules, viruses and their products to and through lymph nodes, the other component of the lymphatic system, to initiate the adaptive immune response. In addition, among the many circulating mediators known to modulate lymphatic contractile activity and thus lymph flow, mediators of inflammation have potent excitatory or inhibitory actions. The involvement of lymphatic vessels in edema resolution, immune cell trafficking and their sensitivity to inflammatory mediators make them pivotal players of the inflammation process. The ability of lymphatic vessels to generate and regulate lymph flow is provided by the lymphatic muscle present in the vessels’ wall. Although molecular studies investigating the mechanisms of lymphatic vessel contraction are still very limited, recent findings suggest that lymphatic pumping requires complicated muscle activities that have similarities to those seen in both the heart (striated muscle) and blood vessels (smooth muscle). This review article focuses on presenting and discussing the mechanisms that regulate lymphatic vessel contraction under normal and pathophysiological states, specifically pertaining to inflammatory conditions. [ABSTRACT FROM AUTHOR]

Abstract: To accomplish its normal roles in body fluid regulation/macromolecular homeostasis, immune function, and lipid absorption; the lymphatic system must transport lymph from the interstitial spaces, into and through the lymphatics, through the lymphatic compartment of the nodes, back into the nodal efferent lymphatics and eventually empty into the great veins. The usual net pressure gradients along this path do not normally favor the passive movement of lymph. Thus, lymph transport requires the input of energy to the lymph to propel it along this path. To do this, the lymphatic system uses a series of pumps to generate lymph flow. Thus to regulate lymph transport, both lymphatic pumping and resistance must be controlled. This review focuses on the regulation of the intrinsic lymph pump by hydrodynamic factors and how these regulatory processes are altered with age. Intrinsic lymph pumping is generated via the rapid/phasic contractions of lymphatic muscle, which are modulated by local physical factors (pressure/stretch and flow/shear). Increased lymph pressure/stretch will generally activate the intrinsic lymph pump up to a point, beyond which the lymph pump will begin to fail. The effect of increased lymph flow/shear is somewhat more complex, in that it can either activate or inhibit the intrinsic lymph pump, depending on the pattern and magnitude of the flow. The pattern and strength of the hydrodynamic regulation of the lymph transport is different in various parts of the lymphatic tree under normal conditions, depending upon the local hydrodynamic conditions. In addition, various pathophysiological processes can affect lymph transport. We have begun to evaluate the influence of the aging process on lymphatic transport characteristics in the rat thoracic duct. The pressure/stretch-dependent activation of intrinsic pumping is significantly impaired in aged rat thoracic duct (TD) and the flow/shear-dependent regulatory mechanisms are essentially completely lacking. The loss of shear-dependent modulation of lymphatic transport appears to be related to a loss of normal eNOS expression and a large rise in iNOS expression in these vessels. Therefore, aging of the lymph transport system significantly impairs its ability to transport lymph. We believe this will alter normal fluid balance as well as negatively impact immune function in the aged animals. Further studies are needed to detail the mechanisms that control and alter lymphatic transport during normal and aged conditions. [Copyright &y& Elsevier]

Breast cancer-related lymphoedema of the arm (BCRL) results from impaired lymph drainage after axillary surgery. Little is known about lymphatic changes in the arm between surgery and oedema onset. We measured forearm muscle and subcutis lymph drainage in 36 women at 7 and 30 months after surgery by quantitative lymphoscintigraphy. None had BCRL initially but 19% had BCRL by 30 months. At 7 months muscle and subcutis drainage in both arms of BCRL-destined women exceeded that of non-BCRL women ( P < 0.01). Muscle lymph drainage always exceeded subcutis drainage ( P < 0.0001). Muscle lymph drainage in the ipsilateral arm was unimpaired relative to the contralateral arm. BCRL therefore developed in women with higher peripheral lymph flows. The major lymphatic load was generated by muscle; there was no pre-BCRL lymphatic impairment in the muscle of the ipsilateral arm. We propose that some women have a defined, constitutive predisposition to secondary lymphoedema. Specifically, women with higher filtration rates, and therefore higher lymph flows through the axilla that are closer to the maximum sustainable, are at greater risk of BCRL following axillary trauma, even following removal of 1–2 nodes. [ABSTRACT FROM AUTHOR]

Multiple investigators have shown interdependence of lymphatic contractions on nitric oxide (NO) activity by pharmacological and traumatic suppression of endothelial NO synthase (eNOS). We demonstrated that lymphatic diastolic relaxation is particularly sensitive to NO from the lymphatic endothelium. The predieted mechanism is shear forces produced by the lymph flow during phasic pumping, activating eNOS in the lymphatic endothelium to produce NO. We measured [NO] during phasic contractions using microelectrodes on in situ mesenteric lymphatics in anesthetized rats under basal conditions and with an intravenous saline bolus (0.5 mIll 00 g) or infusion (0.5 ml 100 g-1∙h-1). Under basal conditions, [NO] measured on the tubular portions of the lymphatics was ∼200-250 nM, slightly higher than in the adjacent adipocyte microvasculature, whereas [NO] measured on the lymphatic bulb surface was ∼400 nM. Immunohistochemistry of eNOS in isolated lympathics indicated a much greater expression in the lymph valves and surrounding bulb area than in the tubular regions. During phasic lymphatic contractions, the valve and tubular [NO] increased with each contractiOn, and during intravenous saline infusion, [NO] increased in proportion to the contraction frequency and, presumably, lymph flow. The partial blockade of eNOS over ∼1 cm length with N°-nitro-L-arginine methyl ester lowered the [NO]. These in vivo data document for the first time that both valvular and tubular lymphatic segments increase NO generation during each phasic contraction and that [NO] summated with increased contraction frequency. The combined data predict regional variations in eNOS and [NO] in the tubular and valve areas, plus the summated NO responses dependent on contraction frequency provide for a complex relaxation mechanism involving NO. [ABSTRACT FROM AUTHOR]

Background: Our objective was to develop an animal model of postsurgical lymphedema that would permit quantitation of edema and lymphatic function after the removal of a single popliteal lymph node in sheep. Methods: As a measure of lymph transport, 125I-human serum albumin was injected into prenodal vessels at 8, 12 and 16 weeks after nodal excision, and plasma levels of the protein tracer were used to calculate the transport rate of the tracer to blood (percent injected per hour). Edema was quantified from the circumferential measurement of the hind limbs. Results and Conclusions: Following nodal excision, the limbs became progressively more edematous up to 3 days after nodectomy. After this, the swelling decreased but had not resolved even at 16 weeks after surgery. Compared with control limbs (17.2 ± 0.6; n = 7), lymphatic function was depressed at 8 weeks after surgery (10.6 ± 1.5; n = 7). At 12 (14.4 ± 1.0; n = 7) and 16 weeks (13.9 ± 1.0; n = 6), regeneration of lymphatic vessels at the excision site helped to restore about 80% of lymphatic capacity. These techniques may be helpful in understanding the pathophysiology associated with cancer-related postsurgical lymphedema and may facilitate the development of new strategies to treat or prevent this condition. Copyright © 2009 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]

T cell migration via afferent lymphatics to draining lymph nodes (dLNs) depends on expression of CCR7 in T cells and CCL21 in the lymphatic vasculature. Once T cells have entered lymphatic capillaries, they slowly migrate into contracting collecting vessels. Here, lymph flow picks up, inducing T cell detachment and rapid transport to the dLNs. We find that the atypical chemokine receptor 4 (ACKR4), which binds and internalizes CCL19 and CCL21, is induced by lymph flow in endothelial cells lining lymphatic collectors, enabling them to scavenge these chemokines. In the absence of ACKR4, migration of T cells to dLNs in TPA-induced inflammation is significantly reduced. While entry into capillaries is not impaired, T cells accumulate in the ACKR4-deficient dermal collecting vessel segments. Overall, our findings identify an ACKR4-mediated mechanism by which lymphatic collectors facilitate the detachment of lymph-borne T cells in inflammation and their transition from crawling to free-flow toward the dLNs. [Display omitted] • ACKR4 is expressed in a flow-dependent manner in afferent lymphatic collectors • ACKR4 scavenges CCR7 ligands like CCL21 and removes them from the collector surface • Chemokine scavenging prevents T cell accumulation in inflamed dermal collectors • In the absence of ACKR4, T cell migration to draining lymph nodes is reduced Friess et al. report that ACKR4 is expressed in a flow-dependent manner in afferent lymphatic collectors, where it removes CCR7 ligands from the collector surface. In inflammation, migrating T cells accumulate in dermal ACKR4-deficient collectors and fail to efficiently de-adhere for flow-mediated, passive transport to draining lymph nodes. [ABSTRACT FROM AUTHOR]

The effects of short-term simulated microgravity on the lymph dynamics of rat lymph nodes were investigated using a combination of Bollman's cage and head-down tilt (HDT). Efferent lymphatics of the iliac and mesenteric lymph nodes were cannulated for the collection of lymph. There was no significant difference in lymph flow rate from the iliac lymph nodes between non-HDT (control) and HDT rats. Lymph flow rate from the mesenteric lymph nodes in HDT rats was slightly higher than that obtained with the control. The cell count obtained from the iliac lymph nodes in HDT rats was significantly larger than those of the controls, while no significant difference in the number of cells from the mesenteric lymph nodes was observed between the control and HDT groups. The cells from the iliac lymph nodes in the control and HDT rats were mostly lymphocytes. The distribution of subsets of lymphocytes (CD3+, CD4+, CD8a+, and CD45R+) from the iliac lymph nodes in HDT rats was not significantly different from the subsets of lymphocytes in the control. Immunization did not affect the distribution of lymphocyte subsets from the iliac lymph nodes in the control and HDT groups. There was no significant difference in the concentrations of lymph albumin in iliac afferent or efferent lymphatics between the control and HDT groups. These findings suggest that HDT posture in Bollman's cage induces transient output of lymphocytes from the iliac lymph nodes of rats in vivo without changing the flow rate, lymphocyte subsets, or concentration of albumin. [ABSTRACT FROM AUTHOR]

In this review, we provide a comprehensive summary of noninvasive imaging modalities used clinically for the diagnosis of lymphatic diseases, new imaging agents for assessing lymphatic architecture and cancer status of lymph nodes, and emerging near-infrared (NIR) fluorescent optical imaging technologies and agents for functional lymphatic imaging. Given the promise of NIR optical imaging, we provide example results of functional lymphatic imaging in mice, swine, and humans, showing the ability of this technology to quantify lymph velocity and frequencies of propulsion resulting from the contractility of lymphatic structures. [ABSTRACT FROM AUTHOR]

The lymphatic system plays critical roles in body fluid and macromolecular homeostasis, lipid absorption, immune function, and metastasis. To accomplish these tasks, the lymphatics must move lymph and its contents from the interstitial space through the lymph vessels and nodes and into the great veins. Contrary to popular belief, lymph does not passively “drain” down this pathway, because the net pressure gradients oppose flow. Instead, the lymphatics must act as both the conduits that direct and regulate lymph flow and the pumps that generate the lymph flow. Thus, to regulate lymph transport and function, both lymphatic pumping and flow resistance must be controlled. Both of these processes occur via regulation of lymphatic muscle contractions, which are classically thought to occur via the interaction of cell calcium with regulatory and contractile proteins. However, our knowledge of this regulation of lymphatic contractile function is far from complete. In this chapter we review our understanding of the important molecular mechanisms, the calcium regulation, and the contractile/regulatory proteins that control lymphatic contractions. A better understanding of these mechanisms could provide the basis for the development of better diagnostic and treatment modalities for lymphatic dysfunction. While progress has been made in our understanding of the molecular biology of lymphangiogenesis as a result of the development of potential lymphangiogenic therapeutic targets, there are currently no therapeutic agents that specifically modulate lymphatic pump function and lymph flow via lymphatic muscle. However, their development will not be possible until the molecular basis of lymphatic contractility is more fully understood. [ABSTRACT FROM AUTHOR]

This chapter discusses the current status of knowledge on basic pressure/stretch– and flow/shear–dependent regulatory reactions of contracting lymphangions in lymphatic vessels. The balance of passive and active lymph pumps is discussed; the data on pressure measurements in different lymphatic nets of several species are provided. The characteristics of typical changes in lymphatic contractility to the increases in transmural pressures are described and discussed, as is the role of pre-existing distension in initiation of lymphatic contractions. The up-to-date status of knowledge on flow-dependent adaptive reactions of contracting lymphangions is provided with detailed characterization of the influences of imposed and contraction-generated flows on lymphatic contractility. The interaction between extrinsic and intrinsic flows in regulation of lymphatic contractility is considered. [ABSTRACT FROM AUTHOR]

Objective: To evaluate the age-related changes in active pumping in thoracic duct (TD) from 24-month-old Fisher-344 rats comparing with TD pumping in 9-month rats. Methods: Lymphatic diameters, contraction amplitude and frequency, ejection fraction, and fractional pump flow were determined in isolated TD preparations. Western blot analyses were performed to evaluate relative levels of eNOS and iNOS in 9- and 24-month-old TD. Results: Stretch-dependent regulation was altered in aged TD especially at higher levels of pressure: the negative inotropy, negative chronotropy and diminished minute pumping (2- to 3-fold decrease) were observed. Physiological NO/imposed-flow-dependent inhibition was completely abolished in aged TD, yet NO-synthase blockade by l-NAME (10- 4 M) increased pumping in a flow-independent manner. Western blot analyses indicated that the relative levels of eNOS were decreased ∼ 7-fold in the 24-month-old TD when compared with 9-month-old TD; whereas iNOS levels were increased ∼ 10-fold in 24-month-old TD. Conclusions: These data provide the first evidence that stretch- and imposed-flow-dependent regulatory mechanisms are greatly altered in aged TD. These alterations of active pumping mechanisms in TD appear to be related with age-related disturbances in NO-dependent regulatory pathways, and may reflect diminished lymphatic muscle contractility as well as altered lymphatic endothelium function. [ABSTRACT FROM AUTHOR]

Vascular endothelial growth factor (VEGF)-C plays an important role in lymphangiogenesis; however, functional responses of lymphatic vessels to VEGF-C have not been characterized. We tested the hypothesis that VEGF-C-induced activation of VEGF receptor (VEGFR)-3 increases lymphatic pump output. We examined the in vivo pump activity of rat mesenteric collecting lymphatics using intravital microscopy during basal conditions and during treatment with 1 nM recombinant VEGF-C, the selective VEGFR-3 agonist VEGF-Cys156Ser mutation (C156S; 1 nM), or 0.1 nM VEGF-A. Their specific responses were also analyzed during selective inhibition of VEGFR-3 with MAZ-51. Contraction frequency, end-diastolic diameter, end-systolic diameter, stroke volume index, pump flow index, and ejection fraction were evaluated. We also assessed arteriolar diameter and microvascular extravasation of FITC-albumin. The results show that both VEGF-C and VEGF-C156S significantly increased contraction frequency, end-diastolic diameter, stroke volume index, and pump flow index in a time-dependent manner. VEGF-A caused a different response characterized by a significantly increased stroke volume after 30 mm of treatment. MAZ-51 (5 µM) caused tonic constriction and decreased contraction frequency. In addition, 0.5 and 5 µM MAZ-51 attenuated VEGF-C- and VEGF-C156S-induced lymphatic pump activation. VEGF-A caused vasodilation of arterioles, whereas VEGF-C and VEGF-C156S did not significantly alter arteriolar diameter. Also, VEGF-A and VEGF-C caused increased microvascular permeability, whereas VEGF-C156S did not. Our results demonstrate that VEGF-C increases lymphatic pumping through VEGFR-3. Furthermore, changes in microvascular hemodynamics are not required for VEGFR-3-mediated changes in lymphatic pump activity. [ABSTRACT FROM AUTHOR]

Although behavior of lymphatic vessels is analogous to that of ventricles, which completely relax between contractions, and blood vessels, which maintain a tonic constriction, the mixture of contractile properties can yield behavior unique to lymphatic vessels. In particular, because of their limited refractory period and slow rate of relaxation, lymphatic vessels lack the contractile properties that minimize summation in ventricles. We, therefore, hypothesized that lymphatic vessels transition to a state of summation when lymphatic vessel contraction frequency exceeds a critical value. We used an isovolumic, con- trolled-flow preparation to compare the time required for full relaxation with the time available to relax during diastole. We measured transmural pressure and diameter on segments of spontaneously contracting bovine mesenteric lymphatic vessels during 10 isovolumic volume steps. We found that beat-to-beat period (frequency-1) decreased with increases in diameter and that total contraction time was constant or slightly increased with diameter. We further found that the convergence of beat-to-beat period and contraction cycle duration predicted a critical transition value, beyond which the vessel does not have time to fully relax. This incomplete relaxation and resulting mechanical summation significantly increase active tension in diastole. Because this transition occurs within a physiological range, contraction summation may represent a fundamental feature of lymphatic vessel function. [ABSTRACT FROM AUTHOR]

Objective: To measure lymphocyte velocity, lymphatic contraction, and shear stress in phasicallycontracting lymphatics in situ. Methods: A high-speed video system was used to capture multiple contraction cycles in rat mesentericlymphatic preparations. The images were analyzed to determine fluid velocity, volume flow rate, wallshear stress, and retrograde flow. Results: Lymphocyte density and flux varied from 326 to 35,500 cells/μL and 206 to 2030 cells/min,respectively. Lymphatics contracted phasically, with a mean diameter 91 ± 9.0 μm and amplitudesof 39%. Lymph velocity varied with the phasic contractions in both direction and magnitude with an average of 0.87 ± 0.18 and peaks of 2.2-9.0 mm/s. The velocity was ∼180° out of phase with the contraction cycle. The average lymph flow was 13.95 ± 5.27 μL/h with transient periods of flowreversal. This resulted in an average shear of 0.64 ± 0.14 with peaks of 4-12 dynes/cm². Conclusions: High-speed lymphocyte tracking provided the spatial and temporal resolution to measurelymphocyte flux throughout the phasic contraction. Poiseuille flow was a reasonable model for estimating wall shear stress through most of the phasic contraction cycle of the intervalvular lymphatic segments. Shear rate was low but had large variations in magnitude compared to that seen in bloodvessels. [ABSTRACT FROM AUTHOR]

Objectives. Plasma hyaluronan is a potentially useful clinical test, especially in liver disease. It rises after eating, but mechanisms by which this occurs are not known. The study aimed at defining the effect of different food and liquid intake on plasma hyaluronan and to address mechanisms. Design. The effects on plasma hyaluronan of ingestion of high-fat and low-fat meals, glucose solution, and saline, and of intravenous metoclopramide and oral cisapride were defined in healthy fasted subjects by serial measurements over 5 h. Hyaluronan was measured by a radiometric assay. Results. After test meals and glucose ingestion, plasma hyaluronan rose to 1.7–13 times the fasting levels in 11 healthy volunteers. Peak values were observed in most subjects 45–90 min after ingestion and reached levels in six subjects that might suggest the presence of hepatic fibrosis or cirrhosis. No change occurred after ingestion of 0.48 L iso-osmotic NaCl solution, equal in bulk to the glucose solution. Stimulation of gastrointestinal motility with metoclopramide had no effect but oral cisapride induced a pattern of elevated plasma hyaluronan which mimicked that induced by foodstuffs. Conclusions. Displacement of hyaluronan from gastrointestinal tissues prevails over the increased clearance expected from elevated portal blood flow. The heightened flux of tissue fluid necessary to displace tissue hyaluronan is best explained by vasodilatation in response to ingestion of nutrients, and subsequent increase in intestinal lymph flow, rather than by fluid absorption, together with gut contraction. The discriminating value of plasma hyaluronan in clinical practice may be greatly enhanced by sampling in fasted subjects at rest. [ABSTRACT FROM AUTHOR]

Because of the role that lymphatics have in fluid and macromolecular exchange, lymphatic function has been tightly tied to the study of the microcirculation for decades. Despite this, our understanding of many basic tenets of lymphatic function is far behind that of the blood vascular system. This is in part due to the difficulty inherent in working in small, thin-walled, clear lymphatic vessels and the relative lack of lymphatic specific molecular/cellular markers. The application of cellular and molecular tools to the field of lymphatic biology has recently produced some significant developments in lymphatic endothelial cell biology. These have propelled our understanding of lymphangiogenesis and related fields forward. Whereas the use of some of these techniques in lymphatic muscle biology has somewhat lagged behind those in the endothelium, recent developments in lymphatic muscle contractile and electrical physiology have also led to advances in our understanding of lymphatic transport function, particularly in the regulation of the intrinsic lymph pump. However, much work remains to be done. This paper reviews significant developments in lymphatic biology and discusses areas where further development of lymphatic biology via classical, cellular, and molecular approaches is needed to significantly advance our understanding of lymphatic physiology. [ABSTRACT FROM AUTHOR]

Aim: The ability to return interstitial protein to central blood is key to the defence against oedema. The aim of this study was to quantify this ability by measuring the rate at which radiolabelled human immunoglobulin (HIgG) accumulated in blood following injection into the subcutis of the hand in normal volunteers and in patients with breast cancer-related lymphoedema (BCRL). Methods: A total of 37 control subjects (healthy normal volunteers or breast cancer patients prior to treatment) and 18 women with BCRL were studied with dual-isotope lymphoscintigraphy. Each received bilateral subcutaneous depot injection in the dorsal web space of HIgG labelled with Tc-99m on one side and In-111 on the other. Activities remaining at the depot and accumulating in blood were measured at regular intervals for 3 h. Clearance from the depot was exponential and expressed as the rate constant kdepot (min–1). Accumulation in blood was essentially linear and, using an estimate of blood volume based on height and weight, was expressed as the linear constant bblood (% administered activity·min–1). The time axis intercept of this linear fit was recorded as an index of the minimum time to arrival of radioprotein in blood. The efficiency with which radioprotein that has left the depot (extra-depot activity) is transported into blood [tissue-to-blood (T-B) transport] was quantified (1) as the quotient bblood/kdepot, and (2) as a function of time after injection by comparing the total amount of radioprotein in blood at any time with the total amount of radioprotein that was no longer in the depot at the same time. Results: Tc-99m-HIgG and In-111-HIgG behaved similarly and are interchangeable. At all times between 60 and 180 min in controls, about 50% of protein that had left the depot was present in blood. T-B transport was reduced to about 20% in BCRL arms in which the hand was involved in swelling (p < 0.001 versus controls), but remained unchanged in patients in whom the hand was spared. The minimum time to arrival of radioprotein in blood was not reduced in BCRL; on the contrary, there appeared to be a small proportion of injected activity that arrived rapidly in blood in BCRL patients but not in controls. Conclusion: We conclude that T-B transport is only impaired in BCRL when radioprotein is injected into swollen tissue. Significant quantities of radioprotein may escape from the arm via local access to blood. Individual variation in this capacity may explain the regional sparing observed in BCRL. Copyright © 2004 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]

The lymphatic clearance of the human skin at the instep of the foot was measured in 20 healthy volunteers (mean age ± SD 33.8 ± 10.5 years). Ten microliters of fluorescein isothiocyanate-dextran 150,000 were injected intradermally and the fluorescent light intensity of the deposit was measured 10 min and 24 h after injection by window densitometry. Fluorescent light intensity decreased by 31.2 ± 13.5 arbitrary units (p < 0.0001) or by a factor of 4.1 ± 3.9. Reproducibility was tested 2–6 weeks later in 7 subjects and an intraclass reliability of 0.76 was found. These are the first measurements of the lymphatic clearance of the human skin using a fluorescent tracer. The method is easier and safer than the isotope clearance technique and small areas of the human skin can be investigated. The data found form a basis with which to compare measurements made in patients with different forms of edema.Copyright © 2001 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]