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Objective: Cardiovascular diseases (CVDs) are the leading cause of death worldwide, with atherosclerosis servingas a primary factor in their development. Platelets, leukocytes, and their interactions play a crucial role ininitiating and amplifying atherosclerosis. This study aims to evaluate the levels of platelet-monocyte aggregates (PMA)and specific integrins involved in leukocyte recruitment, including macrophage-1 antigen (Mac-1) and lymphocytefunction-associated antigen-1 (Lfa-1), in patients with acute coronary syndrome (ACS).Materials and Methods: In this case-control study, thirty-two subjects with ACS and 30 healthy individuals participated.It aimed to evaluate PMA expression and the median fluorescence intensity (MFI) of Mac-1 and Lfa-1 using flowcytometry. Dot plots and Pearson correlation coefficient were employed to examine the relationship between PMA,Mac-1, and Lfa-1. Multilevel model analysis was used to explore the effects and relationships of various parameters,including Mac-1 and Lfa-1, on PMA. Finally, receiver operating characteristic (ROC) curves were utilized to assessthe diagnostic accuracy of PMA, Mac-1, and Lfa-1 markers.Results: It was observed that patients had higher PMA levels compared to the control group (58.99 ± 16.27 vs.29.99 ± 4.19 in controls, P

Objective: Cardiovascular diseases (CVDs) are the leading cause of death worldwide, with atherosclerosis servingas a primary factor in their development. Platelets, leukocytes, and their interactions play a crucial role ininitiating and amplifying atherosclerosis. This study aims to evaluate the levels of platelet-monocyte aggregates (PMA)and specific integrins involved in leukocyte recruitment, including macrophage-1 antigen (Mac-1) and lymphocytefunction-associated antigen-1 (Lfa-1), in patients with acute coronary syndrome (ACS).Materials and Methods: In this case-control study, thirty-two subjects with ACS and 30 healthy individuals participated.It aimed to evaluate PMA expression and the median fluorescence intensity (MFI) of Mac-1 and Lfa-1 using flowcytometry. Dot plots and Pearson correlation coefficient were employed to examine the relationship between PMA,Mac-1, and Lfa-1. Multilevel model analysis was used to explore the effects and relationships of various parameters,including Mac-1 and Lfa-1, on PMA. Finally, receiver operating characteristic (ROC) curves were utilized to assessthe diagnostic accuracy of PMA, Mac-1, and Lfa-1 markers.Results: It was observed that patients had higher PMA levels compared to the control group (58.99 ± 16.27 vs.29.99 ± 4.19 in controls, P<0.001), which correlated with PLT (ρ=0.512, P=0.035). Additionally, CD18 and CD11bexpression on monocytes were significantly elevated in patients (P<0.001) and were positively associated with PMA(β=19.09, P<0.001; β=6.90, P=0.022), but no significant relationship between CD11a and PMA was observed (β=5.06,P=0.315). PMA and Mac-1 were identified as better markers for differentiating patients from healthy individuals.(respectively, AUC=0.94, Sensitivity= 0.84, specificity=0.98; AUC=0.84, Sensitivity= 0.93, specificity=0.70).Conclusion: The study results indicated an increase in both Mac-1 and PMA levels in patients with ACS. Additionally,the significant association observed between Mac-1 and PMA in the patient group suggests a potential relationshipbetween these markers and ACS. [ABSTRACT FROM AUTHOR]

Acute lung injury (ALI), which occurs in association with sepsis, trauma, and coronavirus disease 2019 (COVID‐19), is a serious clinical condition with high mortality. Excessive platelet‐leukocyte aggregate (PLA) formation promotes neutrophil extracellular trap (NET) release and thrombosis, which are involved in various diseases, including ALI. Macrophage‐1 antigen (Mac‐1, CD11b/CD18), which is expressed on the surface of leukocytes, is known to promote NET formation. This study aimed to elucidate the role of Mac‐1 in extracellular histone‐induced ALI. Exogenous histones were administered to Mac‐1‐deficient mice and wild‐type (WT) mice with or without neutrophil or platelet depletion, and several parameters were investigated 1 h after histone injection. Depletion of neutrophils or platelets improved survival time and macroscopic and microscopic properties of lung tissues, and decreased platelet‐leukocyte formation and plasma myeloperoxidase levels. These improvements were also observed in Mac‐1−/− mice. NET formation in Mac‐1−/− bone marrow neutrophils (BMNs) was significantly lower than that in WT BMNs. In conclusion, our findings suggest that Mac‐1 is associated with exacerbation of histone‐induced ALI and the promotion of NET formation in the presence of activated platelets.

Acute lung injury (ALI), which occurs in association with sepsis, trauma, and coronavirus disease 2019 (COVID‐19), is a serious clinical condition with high mortality. Excessive platelet‐leukocyte aggregate (PLA) formation promotes neutrophil extracellular trap (NET) release and thrombosis, which are involved in various diseases, including ALI. Macrophage‐1 antigen (Mac‐1, CD11b/CD18), which is expressed on the surface of leukocytes, is known to promote NET formation. This study aimed to elucidate the role of Mac‐1 in extracellular histone‐induced ALI. Exogenous histones were administered to Mac‐1‐deficient mice and wild‐type (WT) mice with or without neutrophil or platelet depletion, and several parameters were investigated 1 h after histone injection. Depletion of neutrophils or platelets improved survival time and macroscopic and microscopic properties of lung tissues, and decreased platelet‐leukocyte formation and plasma myeloperoxidase levels. These improvements were also observed in Mac‐1−/− mice. NET formation in Mac‐1−/− bone marrow neutrophils (BMNs) was significantly lower than that in WT BMNs. In conclusion, our findings suggest that Mac‐1 is associated with exacerbation of histone‐induced ALI and the promotion of NET formation in the presence of activated platelets. [ABSTRACT FROM AUTHOR]

Background and purposeFollowing inflammatory stimuli, neutrophils are recruited to sites of inflammation and exert effector functions that often have deleterious effects on tissue integrity, which can lead to organ failure. Bruton's tyrosine kinase (Btk) is expressed in neutrophils and constitutes a promising pharmacological target for neutrophil-mediated tissue damage. Here, we evaluate a selective reversible inhibitor of Btk, PRN473, for its ability to dampen neutrophil influx via inhibition of adhesion receptor signalling pathways.Experimental approachIn vitro assays were used to assess fMLP receptor 1 (Fpr-1)-mediated binding of ligands to the adhesion receptors macrophage antigen-1 (Mac-1) and lymphocyte function antigen-1. Intravital microscopy of the murine cremaster was used to evaluate post-adhesion strengthening and endoluminal crawling. Finally, neutrophil influx was visualized in a clinically relevant model of sterile liver injury in vivo. Btk knockout animals were used as points of reference for Btk functions.Key resultsPharmacological inhibition of Btk by PRN473 reduced fMLP-induced phosphorylation of Btk and Mac-1 activation. Biochemical experiments demonstrated the specificity of the inhibitor. PRN473 (20 mg·kg-1 ) significantly reduced intravascular crawling and neutrophil recruitment into inflamed tissue in a model of sterile liver injury, down to levels seen in Btk-deficient animals. A higher dose did not provide additional reduction of intravascular crawling and neutrophil recruitment.Conclusions and implicationsPRN473, a highly selective inhibitor of Btk, potently attenuates sterile liver injury by inhibiting the activation of the β2 -integrin Mac-1 and subsequently neutrophil recruitment into inflamed tissue.

Neutrophil extracellular trap (NET) formation requires chromatin decondensation before nuclear swelling and eventual extracellular release of DNA, which occurs together with nuclear and cytoplasmic antimicrobial proteins. A key mediator of chromatin decondensation is protein deiminase 4 (PAD4), which catalyzes histone citrullination. In the current study, we examined the role of PAD4 and NETosis following activation of neutrophils by A. fumigatus hyphal extract or cell wall β-glucan (curdlan) and found that both induced NET release by human and murine neutrophils. Also, using blocking antibodies to CR3 and Dectin-1 together with CR3-deficient CD18-/- and Dectin-1-/- murine neutrophils, we found that the β-glucan receptor CR3, but not Dectin-1, was required for NET formation. NETosis was also dependent on NADPH oxidase production of reactive oxygen species (ROS). Using an antibody to citrullinated histone 3 (H3Cit) as an indicator of PAD4 activity, we show that β-glucan stimulated NETosis occurs in neutrophils from C57BL/6, but not PAD4-/- mice. Similarly, a small molecule PAD4 inhibitor (GSK484) blocked NET formation by human neutrophils. Despite these observations, the ability of PAD4-/- neutrophils to release calprotectin and kill A. fumigatus hyphae was not significantly different from C57BL/6 neutrophils, whereas CD18-/- neutrophils exhibited an impaired ability to perform both functions. We also detected H3Cit in A. fumigatus infected C57BL/6, but not PAD4-/- corneas; however, we found no difference between C57BL/6 and PAD4-/- mice in either corneal disease or hyphal killing. Taken together, these findings lead us to conclude that although PAD4 together with CR3-mediated ROS production is required for NET formation in response to A. fumigatus, PAD4-dependent NETosis is not required for A. fumigatus killing either in vitro or during infection.

BackgroundAntibody-mediated rejection (AMR) of most solid organs is characterized by evidence of complement activation and/or intragraft macrophages (C4d + and CD68+ biopsies). We previously demonstrated that crosslinking of HLA I by antibodies triggered endothelial activation and monocyte adhesion. We hypothesized that activation of the classical complement pathway at the endothelial cell surface by HLA antibodies would enhance monocyte adhesion through soluble split product generation, in parallel with direct endothelial activation downstream of HLA signaling.MethodsPrimary human aortic endothelial cells (HAEC) were stimulated with HLA class I antibodies in the presence of intact human serum complement. C3a and C5a generation, endothelial P-selectin expression, and adhesion of human primary and immortalized monocytes (Mono Mac 6) were measured. Alternatively, HAEC or monocytes were directly stimulated with purified C3a or C5a. Classical complement activation was inhibited by pretreatment of complement with an anti-C1s antibody (TNT003).ResultsTreatment of HAEC with HLA antibody and human complement increased the formation of C3a and C5a. Monocyte recruitment by human HLA antibodies was enhanced in the presence of intact human serum complement or purified C3a or C5a. Specific inhibition of the classical complement pathway using TNT003 or C1q-depleted serum significantly reduced adhesion of monocytes in the presence of human complement.ConclusionsDespite persistent endothelial viability in the presence of HLA antibodies and complement, upstream complement anaphylatoxin production exacerbates endothelial exocytosis and leukocyte recruitment. Upstream inhibition of classical complement may be therapeutic to dampen mononuclear cell recruitment and endothelial activation characteristic of microvascular inflammation during AMR.

There is compelling evidence that circulatory hemodynamics prevent neutrophil activation, including adhesion to microvessels, in the microcirculation. However, the underlying mechanism or mechanisms by which that mechanoregulation occurs remain unresolved. Here, we report evidence that exposure to fluid shear stress (FSS) promotes neutrophils to release cathepsin B (ctsB) and that this autocrine regulatory event is antiadhesive for neutrophils on endothelial surfaces through Mac1-selective regulation. We used a combined cell-engineering and immunocytochemistry approach to find that ctsB was capable of cleaving Mac1 integrins on neutrophils and demonstrated that this proteolysis alters their adhesive functions. Under no-flow conditions, ctsB enhanced neutrophil migration though a putative effect on pseudopod retraction rates. We also established a flow-based cell detachment assay to verify the role of ctsB in the control of neutrophil adhesion by fluid flow stimulation. Fluid flow promoted neutrophil detachment from platelet and endothelial layers that required ctsB, consistent with its fluid shear stress-induced release. Notably, compared with leukocytes from wild-type mice, those from ctsB-deficient (ctsB -/- ) mice exhibited an impaired CD18 cleavage response to FSS, significantly elevated baseline levels of CD18 surface expression, and an enhanced adhesive capacity to mildly inflamed postcapillary venules. Taken together, the results of the present study support a role for ctsB in a hemodynamic control mechanism that is antiadhesive for leukocytes on endothelium. These results have implications in the pathogenesis of chronic inflammation, microvascular dysfunction, and cardiovascular diseases involving sustained neutrophil activation in the blood and microcirculation.

Cancer cells elude anti-tumour immunity through multiple mechanisms, including upregulated expression of ligands for inhibitory immune checkpoint receptors. Phagocytosis by macrophages plays a critical role in cancer control. Therapeutic blockade of signal regulatory protein (SIRP)-α, an inhibitory receptor on macrophages, or of its ligand CD47 expressed on tumour cells, improves tumour cell elimination in vitro and in vivo, suggesting that blockade of the SIRPα-CD47 checkpoint could be useful in treating human cancer. However, the pro-phagocytic receptor(s) responsible for tumour cell phagocytosis is(are) largely unknown. Here we find that macrophages are much more efficient at phagocytosis of haematopoietic tumour cells, compared with non-haematopoietic tumour cells, in response to SIRPα-CD47 blockade. Using a mouse lacking the signalling lymphocytic activation molecule (SLAM) family of homotypic haematopoietic cell-specific receptors, we determined that phagocytosis of haematopoietic tumour cells during SIRPα-CD47 blockade was strictly dependent on SLAM family receptors in vitro and in vivo. In both mouse and human cells, this function required a single SLAM family member, SLAMF7 (also known as CRACC, CS1, CD319), expressed on macrophages and tumour cell targets. In contrast to most SLAM receptor functions, SLAMF7-mediated phagocytosis was independent of signalling lymphocyte activation molecule-associated protein (SAP) adaptors. Instead, it depended on the ability of SLAMF7 to interact with integrin Mac-1 (refs 18, 19, 20) and utilize signals involving immunoreceptor tyrosine-based activation motifs. These findings elucidate the mechanism by which macrophages engulf and destroy haematopoietic tumour cells. They also reveal a novel SAP adaptor-independent function for a SLAM receptor. Lastly, they suggest that patients with tumours expressing SLAMF7 are more likely to respond to SIRPα-CD47 blockade therapy.

Integrin activation is required for neutrophil functions. Impaired integrin activation on neutrophils is the hallmark of leukocyte adhesion deficiency (LAD) syndrome in humans, characterized by impaired leukocyte recruitment and recurrent infections. The Src kinase-associated phosphoprotein 2 (Skap2) is involved in integrin functions in different leukocyte subtypes. However, the role of Skap2 in β2 integrin activation and neutrophil recruitment is unknown. In this study, we demonstrate the crucial role of Skap2 in regulating actin polymerization and binding of talin-1 and kindlin-3 to the β2 integrin cytoplasmic domain, thereby being indispensable for β2 integrin activation and neutrophil recruitment. The direct interaction of Skap2 with the Wiskott-Aldrich syndrome protein via its SH3 domain is critical for integrin activation and neutrophil recruitment in vivo. Furthermore, Skap2 regulates integrin-mediated outside-in signaling events and neutrophil functions. Thus, Skap2 is essential to activate the β2 integrins, and loss of Skap2 function is sufficient to cause a LAD-like phenotype in mice.

Brennan J Blight, Amarbir S Gill, Jorgen S Sumsion, Chelsea E Pollard, Shaelene Ashby, Gretchen M Oakley, Jeremiah A Alt, Abigail Pulsipher Division of Otolaryngology-Head and Neck Surgery, Rhinology-Sinus and Skull Base Surgery Program, Department of Surgery, University of Utah School of Medicine, Salt Lake City, UT, USACorrespondence: Abigail PulsipherDivision of Otolaryngology-Head and Neck Surgery, Rhinology-Sinus and Skull Base Surgery Program, Department of Surgery, University of Utah School of Medicine, 50 North Medical Drive, Room 3C120, Salt Lake City, UT, 84132, USAEmail abigail.pulsipher@utah.eduPurpose: Chronic rhinosinusitis with nasal polyps (CRSwNP) is predominantly characterized by eosinophil- and T helper 2 cell (Th2)-biased inflammation. Integrins and intercellular adhesion molecules (ICAMs) are superfamilies of cell adhesion molecules (CAMs) that facilitate the recruitment and trafficking of immune cells and have been implicated in coordinating eosinophil and Th2 cell adhesion and signaling in asthma. The roles of CAMs in CRSwNP, however, remain poorly understood. The purpose of this study was to characterize the systemic and local expression of CAMs and identify which CAMs are potentially involved in CRSwNP pathology.Materials and Methods: A prospective observational study was conducted using peripheral blood and anterior ethmoid tissues of patients with CRSwNP (n=32) and controls (n=15). Multiplex gene analysis and Pearson correlations were performed to identify associations between systemically and locally expressed CAMs. Based on the gene expression results, immunohistochemical evaluation and quantification of cells expressing integrins ITGAM, ITGAX, and ITGB2, as well as ICAM-3 in sinonasal tissues were conducted to compare local protein expression patterns.Results: Integrin and ICAM genes were significantly elevated in the blood (p< 0.001 to p< 0.05) and sinuses (p< 0.0003 to p< 0.05) of patients with CRSwNP compared to controls. Strong positive correlations of genes expressed in the blood (p< 0.01 to p< 0.05) and sinuses (p< 0.01) were observed between ITGAM, ITGAX, ITGB2, and ICAM3. ITGAM-, ITGB2-, ICAM-3-, and ICAM-3/ITGB2-positive cell counts were significantly increased in CRSwNP compared to controls (p< 0.0001 to p< 0.04), and a positive correlation between ICAM-3/ITGB2- and ITGAM-positive cell counts was observed (p< 0.02).Conclusion: The systemic and local expression of ITGAM, ITGB2, and ICAM-3 is significantly upregulated in CRSwNP, suggesting that integrin complex ITGAM/ITGB2 and ICAM-3 serve a potential role in inflammation-mediated signaling in CRSwNP.Keywords: integrins, intercellular adhesion molecule 3, macrophage-1 antigen, Th2 pathophysiology, transcriptional analysis, allergy, asthma

The complement system has been implicated in the removal of dysfunctional synapses and neurites during development and in disease processes in the mouse, but it is unclear how far the mouse data can be transferred to humans. Here, we co-cultured macrophages derived from human THP1 monocytes and neurons derived from human induced pluripotent stem cells, to study the role of the complement system in a human model. Components of the complement system were expressed by the human macrophages and human neuronal culture, while receptors of the complement cascade were expressed by human macrophages as shown via gene transcript analysis and flow cytometry. We mimicked pathological conditions leading to an altered glycocalyx by treatment of human neurons with sialidases. Desialylated human neurites were opsonized by the complement component C1q. Furthermore, human neurites with an intact sialic acid cap remained untouched, while desialylated human neurites were removed and ingested by human macrophages. While blockage of the complement receptor 1 (CD35) had no effect, blockage of CD11b as part of the complement receptor 3 (CR3) reversed the effect on macrophage phagocytosis of desialylated human neurites. Data demonstrate that in the human system sialylation of the neuronal glycocalyx serves as an inhibitory flag for complement binding and CR3-mediated phagocytosis by macrophages.

Background: Integrins mediate the adhesion, crawling, and migration of neutrophils during vascular inflammation. Thiol exchange is important in the regulation of integrin functions. ERp72 (endoplasmic reticulum-resident protein 72) is a member of the thiol isomerase family responsible for the catalysis of disulfide rearrangement. However, the role of ERp72 in the regulation of Mac-1 (integrin αMβ2) on neutrophils remains elusive., Methods: Intravital microscopy of the cremaster microcirculation was performed to determine in vivo neutrophil movement. Static adhesion, flow chamber, and flow cytometry were used to evaluate in vitro integrin functions. Confocal fluorescent microscopy and coimmunoprecipitation were utilized to characterize the interactions between ERp72 and Mac-1 on neutrophil surface. Cell-impermeable probes and mass spectrometry were used to label reactive thiols and identify target disulfide bonds during redox exchange. Biomembrane force probe was performed to quantitatively measure the binding affinity of Mac-1. A murine model of acute lung injury induced by lipopolysaccharide was utilized to evaluate neutrophil-associated vasculopathy., Results: ERp72-deficient neutrophils exhibited increased rolling but decreased adhesion/crawling on inflamed venules in vivo and defective static adhesion in vitro. The defect was due to defective activation of integrin Mac-1 but not LFA-1 (lymphocyte function-associated antigen-1) using blocking or epitope-specific antibodies. ERp72 interacted with Mac-1 in lipid rafts on neutrophil surface leading to the reduction of the C654-C711 disulfide bond in the αM subunit that is critical for Mac-1 activation. Recombinant ERp72, via its catalytic motifs, increased the binding affinity of Mac-1 with ICAM-1 (intercellular adhesion molecule-1) and rescued the defective adhesion of ERp72-deficient neutrophils both in vitro and in vivo. Deletion of ERp72 in the bone marrow inhibited neutrophil infiltration, ameliorated tissue damage, and increased survival during murine acute lung injury., Conclusions: Extracellular ERp72 regulates integrin Mac-1 activity by catalyzing disulfide rearrangement on the αM subunit and may be a novel target for the treatment of neutrophil-associated vasculopathy., Competing Interests: Disclosures None.

Perivascular microglia activation is a hallmark of inflammatory demyelination in multiple sclerosis (MS), but the mechanisms underlying microglia activation and specific strategies to attenuate their activation remain elusive. Here, we identify fibrinogen as a novel regulator of microglia activation and show that targeting of the interaction of fibrinogen with the microglia integrin receptor Mac-1 (alpha(M)beta(2), CD11b/CD18) is sufficient to suppress experimental autoimmune encephalomyelitis in mice that retain full coagulation function. We show that fibrinogen, which is deposited perivascularly in MS plaques, signals through Mac-1 and induces the differentiation of microglia to phagocytes via activation of Akt and Rho. Genetic disruption of fibrinogen-Mac-1 interaction in fibrinogen-gamma(390-396A) knock-in mice or pharmacologically impeding fibrinogen-Mac-1 interaction through intranasal delivery of a fibrinogen-derived inhibitory peptide (gamma(377-395)) attenuates microglia activation and suppresses relapsing paralysis. Because blocking fibrinogen-Mac-1 interactions affects the proinflammatory but not the procoagulant properties of fibrinogen, targeting the gamma(377-395) fibrinogen epitope could represent a potential therapeutic strategy for MS and other neuroinflammatory diseases associated with blood-brain barrier disruption and microglia activation.

Perivascular microglia activation is a hallmark of inflammatory demyelination in multiple sclerosis (MS), but the mechanisms underlying microglia activation and specific strategies to attenuate their activation remain elusive. Here, we identify fibrinogen as a novel regulator of microglia activation and show that targeting of the interaction of fibrinogen with the microglia integrin receptor Mac-1 (alpha(M)beta(2), CD11b/CD18) is sufficient to suppress experimental autoimmune encephalomyelitis in mice that retain full coagulation function. We show that fibrinogen, which is deposited perivascularly in MS plaques, signals through Mac-1 and induces the differentiation of microglia to phagocytes via activation of Akt and Rho. Genetic disruption of fibrinogen-Mac-1 interaction in fibrinogen-gamma(390-396A) knock-in mice or pharmacologically impeding fibrinogen-Mac-1 interaction through intranasal delivery of a fibrinogen-derived inhibitory peptide (gamma(377-395)) attenuates microglia activation and suppresses relapsing paralysis. Because blocking fibrinogen-Mac-1 interactions affects the proinflammatory but not the procoagulant properties of fibrinogen, targeting the gamma(377-395) fibrinogen epitope could represent a potential therapeutic strategy for MS and other neuroinflammatory diseases associated with blood-brain barrier disruption and microglia activation.

In a transgenic model of multi-stage squamous carcinogenesis induced by human papillomavirus (HPV) oncogenes, infiltrating CD4+ T cells can be detected in both premalignant and malignant lesions. The lymph nodes that drain sites of epidermal neoplasia contain activated CD4+ T cells predominantly reactive toward Staphylococcal bacterial antigens. HPV16 mice deficient in CD4+ T cells were found to have delayed neoplastic progression and a lower incidence of tumors. This delay in carcinogenesis is marked by decreased infiltration of neutrophils, and reduced activity of matrix metalloproteinase-9, an important cofactor for tumor progression in this model. The data reveal an unexpected capability of CD4 T cells, whereby, proinflammatory CD4+ T cells, apparently responding to bacterial infection of dysplastic skin lesions, can inadvertently enhance neoplastic progression to invasive cancer.

Interactions among leukocytes and leukocytes with immune-associated auxiliary cells represent an essential feature of the immune response that requires the involvement of cell adhesion molecules (CAMs). In the immune system, CAMs include a wide range of members pertaining to different structural and functional families involved in cell development, activation, differentiation and migration. Among them, β 2 integrins (LFA-1, Mac-1, p150,95 and α D β 2 ) are predominantly involved in homotypic and heterotypic leukocyte adhesion. β2 integrins bind to intercellular (I)CAMs, actin cytoskeleton-linked receptors belonging to immunoglobulin superfamily (IgSF)-CAMs expressed by leukocytes and vascular endothelial cells, enabling leukocyte activation and transendothelial migration. β2 integrins have long been viewed as the most important ICAMs partners, propagating intracellular signalling from β2 integrin-ICAM adhesion receptor interaction. In this review, we present previous evidence from pioneering studies and more recent findings supporting an important role for ICAMs in signal transduction. We also discuss the contribution of immune ICAMs (ICAM-1, -2, and -3) to reciprocal cell signalling and function in processes in which β2 integrins supposedly take the lead, paying particular attention to T cell activation, differentiation and migration.

Trichomonas vaginalis (Tv) is a parasite that causes trichomoniasis, a prevalent sexually-transmitted infection. Neutrophils are found at the site of infection, and can rapidly kill the parasite in vitro, using trogocytosis. However, the specific molecular players in neutrophil killing of Tv are unknown. Here, we show that complement proteins play a role in Tv killing by human neutrophil-like cells (NLCs). Using CRISPR/Cas9, we generated NLCs deficient in each of three complement receptors (CRs) known to be expressed on human neutrophils: CR1, CR3, and CR4. Using in vitro trogocytosis assays, we found that CR3, but not CR1 or CR4 is required for maximum trogocytosis of the parasite by NLCs, with NLCs lacking CR3 demonstrating ~40% reduction in trogocytosis, on average. We also observed a reduction in NLC killing of Tv in CR3 knockout, but not CR1 or CR4 knockout NLCs. On average, NLCs lacking CR3 had ~50% reduction in killing activity. We also used a parallel approach of pre-incubating NLCs with blocking antibodies against CR3, which similarly reduced NLC killing of parasites. These data support a model in which Tv is opsonized by the complement protein iC3b, and bound by neutrophil CR3 receptor, to facilitate trogocytic killing of the parasite., (© 2024 The Authors. Parasite Immunology published by John Wiley & Sons Ltd.)

Since the successful introduction of checkpoint inhibitors targeting the adaptive immune system, monoclonal antibodies inhibiting CD47-SIRPα interaction have shown promise in enhancing anti-tumor treatment efficacy. Apart from SIRPα, neutrophils express a broad repertoire of inhibitory receptors, including several members of the sialic acid-binding receptor (SIGLEC) family. Here, we demonstrate that interaction between tumor cell-expressed sialic acids and SIGLEC-5/14 on neutrophils inhibits antibody-dependent cellular cytotoxicity (ADCC). We observed that conjugate formation and trogocytosis, both essential processes for neutrophil ADCC, were limited by the sialic acid-SIGLEC-5/14 interaction. During neutrophil-tumor cell conjugate formation, we found that inhibition of the interaction between tumor-expressed sialic acids and SIGLEC-5/14 on neutrophils increased the CD11b/CD18 high affinity conformation. By dynamic acoustic force measurement, the binding between tumor cells and neutrophils was assessed. The interaction between SIGLEC-5/14 and the sialic acids was shown to inhibit the CD11b/CD18-regulated binding between neutrophils and antibody-opsonized tumor cells. Moreover, the interaction between sialic acids and SIGLEC-5/14-consequently hindered trogocytosis and tumor cell killing. In summary, our results provide evidence that the sialic acid-SIGLEC-5/14 interaction is an additional target for innate checkpoint blockade in the tumor microenvironment.

We have shown previously that the 5-lipoxygenase product 5-oxo-6,8, 11,14-eicosatetraenoic acid (5-oxo-ETE) is a highly potent eosinophil chemoattractant in vitro. To determine whether this substance can induce pulmonary eosinophil infiltration in vivo, it was administered to Brown Norway rats by tracheal insufflation. Eosinophils were then counted in lung sections that had been immunostained with an antibody to eosinophil major basic protein. 5-Oxo-ETE induced a dramatic increase in the numbers of eosinophils (ED50, 2.5 microg) around the walls of the airways, which reached maximal levels (five times control levels) between 15 and 24 h after administration, and then declined. LTB4 also induced pulmonary eosinophil infiltration with a similar ED50 but appeared to be somewhat less effective. In contrast, LTD4 and LTE4 were inactive. 5-Oxo-ETE-induced eosinophilia was unaffected by the LTB4 and PAF antagonists LY255283 and WEB 2170, respectively. However, it was inhibited by approximately 75% by monoclonal antibodies to CD49d (VLA-4) or CD11a (LFA-1) but was not significantly affected by an antibody to CD11b (Mac-1). In conclusion, 5-oxo-ETE induces pulmonary eosinophilia in Brown Norway rats, raising the possibility that it may be a physiological mediator of inflammation in asthma.

The distal airway of the lung is innervated by vagus nerve. Upon stimulation, vagus nerve endings release acetylcholine or neuropeptides via C-fiber afferents to regulate lung infection and immunity. Vagal sensory nerve endings, brain integration center, acetylcholine and α7 nicotinic acetylcholine receptor (nAChR) expressing cells are key components of pulmonary parasympathetic inflammatory reflex. Meanwhile, this local machinery synergizes with spleen (as a functional hub of cholinergic anti-inflammatory pathway) to finely tune recruitment of the splenic α7 nAChR+CD11b+ cells into the inflamed lungs during lung infection. Recent studies have showed that lung group 2 innate lymphoid cells (ILC2) express both α7 nAChR and neuropeptide receptors. Acetylcholine and neuropeptides can regulate ILC2 and reshape pulmonary infection and immunity. Among the airway epithelial cells, pulmonary neuroendocrine cells are rare cell population; however, these cells are innervated by sensory nerve endings and they could secrete neuropeptides that influence lung infection and immunity. [ABSTRACT FROM AUTHOR]

Adhesion of blood leukocytes to the endothelium involves multiple steps including initial attachment (tethering), rolling, and firm arrest. Presentation of adhesion molecules on leukocyte microvilli can substantially enhance tethering. Localization of L-selectin to microvilli and of CD44 to the planar cell body have been shown to depend upon their transmembrane and cytoplasmic domains. We investigated the role of leukocyte integrin transmembrane and cytoplasmic domains in initiating adhesion under flow and in microvillous localization. Integrins alpha4beta7, alphaLbeta2, and alphaMbeta2 were heterologously expressed in K562 cells. alpha4beta7 initiated adhesion under flow and localized to microvilli, whereas beta2 integrins did not initiate adhesion and localized to the cell body. Chimeric integrins were produced by replacing the alpha4beta7 cytoplasmic and/or transmembrane domains with the homologous domains of alphaLbeta2 or alphaMbeta2. Unexpectedly, these chimeras efficiently mediated adhesion to the alpha4beta7 ligand mucosal addressin cell adhesion molecule-1 under flow and localized to microvilli. Therefore, differences between the transmembrane and cytoplasmic domains of alpha4 and beta2 integrins do not account for differences in ability to support attachment under flow or in membrane localization. Integrins alpha4beta1, alpha5beta1, alpha6Abeta1, alphavbeta3, and alphaEbeta7 also localized to microvilli. Transmembrane proteins known or suspected to associate with extracellular domains of microvillous integrins, including tetraspans and CD47, were concentrated on microvilli as well. These findings suggest that interactions between the extracellular domains of integrins and associated proteins could direct the assembly of multimolecular complexes on leukocyte microvilli.

We have used immunocytochemical techniques and enzyme cytochemistry to examine the distribution of plasma membrane proteins during coiling phagocytosis of Legionella pneumophila and conventional phagocytosis of Escherichia coli. Whereas class I and class II major histocompatibility complex (MHC) molecules are relatively excluded from nascent phagosomes during conventional and coiling phagocytosis, the CR3 complement receptor persists in nascent phagosomes. The staining pattern for alkaline phosphatase activity resembles that of MHC molecules, with a marked exclusion of phosphatase activity from L. pneumophila coils and nascent phagosomes. The staining pattern for 5'-nucleotidase activity, on the other hand, resembles that of CR3 with intense staining in the inner layers of L. pneumophila coils. These results demonstrate that the cell has the ability to exclude selectively certain membrane proteins from the nascent phagosome during phagocytosis, thereby producing a phagosomal membrane markedly different from the plasma membrane from which it is derived.

Background Deficiency of hypoxia-induced factor-1α (HIF-1α) in macrophages reduced lipopolysaccharide (LPS)-induced mortality; however, whether HIF-1α expression in myeloid cells would contribute to the development of Escherichia coli (E. coli) or LPS-induced acute lung injury (ALI) is less investigated. Aim To test whether deletion of Hif1α in myeloid cells affects E. coli or LPS-induced ALI and to elicit the underlying mechanisms. Design Laboratory study. Methods We intratracheally challenged Hif1αfl/fl and Hif1αfl/fl LysMCre mice with E. coli or LPS to analyze lung and spleen inflammatory responses. Flow cytometry was used to analyze the changes of α7 nAChR+CD11b+ cells in the lung and spleen. Double knockout of Chrna7 and Itgam mice were used to examine expression of HIF-1α during E. coli lung infection. Vagotomy was performed to demonstrate the role of vagus nerve in mediating protective effects of deletion of Hif1α in myeloid cells on LPS-induced ALI. Results Deletion of Hif1α in myeloid cells could reduce lung edema, inflammatory cell infiltration, and lung and BAL inflammatory cytokines in E. coli -induced ALI. Flow cytometric analysis revealed that α7 nAChR+CD11b+ cells in the lung and spleen were markedly increased in E. coli -challenged Hif1αfl/fl LysMCre mice compared with E. coli -challenged Hif1αfl/fl mice. Double knockout of Chrna7 and Itgam increased HIF-1α expression in lung and spleen cells during lung E. coli infection. Vagotomy abolished the protective effect of deletion of Hif1α in myeloid cells on LPS-induced ALI. Conclusion Deletion of Hif1α in myeloid cells could protect mice from lung injury depending on α7 nAChR+CD11b+ cells and innervation of vagal circuits. [ABSTRACT FROM AUTHOR]

Blood-brain barrier (BBB) disruption, thrombus formation and immune-mediated inflammation are important steps in the pathophysiology of cerebral ischemia–reperfusion injury but are still inaccessible to therapeutic interventions. Recent studies have provided increasing evidence that blocking of platelet glycoprotein (GP) receptor Ib might represent a novel target in treating acute ischemic stroke. This research was conducted to explore the therapeutic efficacy and potential mechanisms of GPIbα inhibitor (anfibatide) in a model of brain ischemia–reperfusion injury in mice. Male mice underwent 90 min of right middle cerebral artery occlusion (MCAO) followed by 24 h of reperfusion. Anfibatide (1, 2, 4 ug/kg) or tirofiban were administered intravenously 1 h after reperfusion. The results showed that anfibatide could significantly reduce infarct volumes, increase the number of intact neuronal cells and improve neurobehavioral function. Moreover, anfibatide could reduce post ischemic BBB damage by attenuating increased paracellular permeability in the ischemia hemisphere significantly. Stroke-induced increases in activity and protein expression of macrophage-1 antigen (MAC-1) and P-selectin were also reduced by anfibatide intervention. Finally, anfibatide exerted antithrombotic effects upon stroke by decreased the number of microthrombi formation. This is the first demonstration of anfibatide’s efficacy in protecting the BBB integrity and decreasing neutrophil inflammation response mediated by MAC-1 besides microthrombus formation inhibition in the brain during reperfusion. Anfibatide, as a promising anti-thrombo-inflammation agent, could be beneficial for the treatment of ischemic stroke. [ABSTRACT FROM AUTHOR]

Aneurysm formation occurs most frequently as abdominal aortic aneurysm (AAA), but is also seen in other localizations like thoracic or peripheral aneurysm. While initial mechanisms for aneurysm induction remain elusive, observations from AAA samples show transmural inflammation with proteolytic imbalance and repair mechanisms triggered by the innate immune system. However, limited knowledge exists about aneurysm pathology, especially for others than AAA. We compared 42 AAA, 15 popliteal, 3 ascending aortic, five iliac, two femoral, two brachial, one visceral and two secondary aneurysms to non-aneurysmatic controls by histologic analysis, immunohistochemistry and cytokine expression. Muscular and elastic type arteries show a uniform way of aneurysm formation. All samples show similar morphology. The changes compared to controls are distinct and include matrix remodeling with smooth muscle cell phenotype switch and angiogenesis, adventitial lymphoid cell accumulation and M1 macrophage homing together with neutrophil inflammation. Inflammatory cytokines are up-regulated accordingly. Comparative analysis of different disease entities can identify characteristic pathomechanisms. The phenotype of human advanced aneurysm disease is observed for elastic and muscular type arteries, does not differ between disease localizations and might, thus, be a unique response of the vasculature to the still unknown trigger of aneurysm formation. [ABSTRACT FROM AUTHOR]

Sepsis continues to result in high morbidity and mortality. General anesthesia is often administered to septic patients, but the impacts of general anesthesia on host defense are not well understood. General anesthesia can be given by volatile and intravenous anesthetics. Our previous in vitro study showed that volatile anesthetic isoflurane directly inhibits leukocyte function-associated antigen-1 (LFA-1) and macrophage-1 antigen (Mac-1), critical adhesion molecules on leukocytes. Thus, the role of isoflurane exposure on in vivo LFA-1 and Mac-1 function was examined using polymicrobial abdominal sepsis model in mice. As a comparison, intravenous anesthetic propofol was given to a group of mice. Wild type, LFA-1, Mac-1, and adhesion molecule-1 knockout mice were used. Following the induction of polymicrobial abdominal sepsis by cecal ligation and puncture, groups of mice were exposed to isoflurane for either 2 or 6 h, or to propofol for 6h, and their outcomes were examined. Bacterial loads in tissues and blood, neutrophil recruitment to the peritoneal cavity and phagocytosis were studied. Six hours of isoflurane exposure worsened the outcome of abdominal sepsis (P < .0001) with higher bacterial loads in tissues, but 2h of isoflurane or 6 h of propofol exposure did not. Isoflurane impaired neutrophil recruitment to the abdominal cavity by inhibiting LFA-1 function. Isoflurane also impaired bacterial phagocytosis via complement receptors including Mac-1. In conclusion, prolonged isoflurane exposure worsened the outcome of experimental polymicrobial abdominal sepsis and was associated with impaired neutrophil recruitment and bacterial phagocytosis via reduced LFA-1 and Mac-1 function. [ABSTRACT FROM AUTHOR]

The roots of Abrus precatorius (AP, Fabaceae) have traditionally been used in Vietnam and China for the treatment of inflammatory diseases such as stomatitis, asthma, bronchitis, and hepatitis. Therefore, in this study, we isolated 4-methoxylonchocarpin (ML), an anti-inflammatory compound present in AP, and studied its anti-inflammatory effects in mice with 2,4,6-trinitrobenzenesulfonic acid (TNBS)-induced colitis. In lipopolysaccharide (LPS)-stimulated macrophages, ML was found to inhibit nuclear factor (NF)-κB activation and tumor necrosis factor (TNF) and interleukin (IL)-6 expression by inhibiting LPS binding to Toll-like receptor 4 (TLR4) in vitro. Oral administration of ML in mice with TNBS-induced colitis suppressed colon shortening and colonic myeloperoxidase activity. ML treatment significantly inhibited the activation of nuclear factor (NF)-κB and phosphorylation of transforming growth factor β-activated kinase 1 in the colon. Treatment with ML also inhibited TNBS-induced expression of IL-1β, IL-17A, and TNF. While ML reduced the TNBS-induced expression of M1 macrophage markers such as arginase-2 and TNF, it was found to increase the expression of M2 macrophage markers such as arginase-1 and IL-10. In conclusion, oral administration of ML attenuated colitis in mice by inhibiting the binding of LPS to TLR4 on immune cells and increasing the polarization of M1 macrophages to M2 macrophages. [ABSTRACT FROM AUTHOR]