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Plasmacytoid dendritic cells (pDC), a highly specialized class of innate immune cells that serve as rapid sensors of danger signals in circulation or in lymphoid tissue are well studied. However, there remains knowledge gaps about age-dependent changes of pDC function in the intestinal mucosa. Here, we report that under homeostatic conditions, the proportion of pDC expressing C-C chemokine receptor 9 (CCR9) in the intestinal intraepithelial cell (iIEC) population is comparable between young (2-4 months) and aged (18-24 months) mice, but the absolute numbers of iIEC and pDC are significantly lower in aged mice. Employing the classic model of acute endotoxemia induced by lipopolysaccharide (LPS), we found a decrease in the proportion and absolute number of intraepithelial pDC in both young and aged mice despite the LPS-induced increased expression of the chemokine C-C ligand 25 (CCL25), the ligand of CCR9, in the intestinal mucosa of young mice. In adoptive transfer experiments, a significantly lower number of pDC was retained into the intestinal layer of aged host mice after LPS administration. This was associated with recoverable pDC numbers in the intestinal lumen. Furthermore, co-adoptive transfer of young and aged pDC into young hosts also showed significantly lower retention of aged pDC in the epithelial layer compared to the co-transferred young pDC. Collectively, these data show age-associated changes in mucosal CCL25 gene expression and in pDC number. These may underlie the reported inadequate responses to gastrointestinal pathogens during chronologic aging.

Fibroblastic reticular cells (FRCs), a subpopulation of stromal cells in lymphoid organs and fat-associated lymphoid clusters (FALCs) in adipose tissue, play immune-regulatory roles in the host response to infection and may be useful as a form of cell therapy in sepsis. Here, we found an unexpected major role of TLR9 in controlling peritoneal immune cell recruitment and FALC formation at baseline and after sepsis induced by cecal ligation and puncture (CLP). TLR9 regulated peritoneal immunity via suppression of chemokine production by FRCs. Adoptive transfer of TLR9-deficient FRCs more effectively decreased mortality, bacterial load, and systemic inflammation after CLP than WT FRCs. Importantly, we found that activation of TLR9 signaling suppressed chemokine production by human adipose tissue-derived FRCs. Together, our results indicate that TLR9 plays critical roles in regulating peritoneal immunity via suppression of chemokine production by FRCs. These data form a knowledge basis upon which to design new therapeutic strategies to improve the therapeutic efficacy of FRC-based treatments for sepsis and immune dysregulation diseases.

Sepsis is defined as infection with organ dysfunction due to a dysregulated immune response. The lung is one of the most vulnerable organs at the onset of sepsis. Interleukin (IL)-33 can be released by injured epithelial and endothelial cells in the lung and regulate immune activation and infiltration. Therefore, we postulated that IL-33 would contribute to the immune response in the lung during sepsis. Using the cecal ligation and puncture (CLP) sepsis model, we show here that IL-33 contributes significantly to both sepsis-induced inflammation in the lung and systemic inflammatory response in the early phase of sepsis. Despite the higher intra-peritoneal bacterial burden, the absence of IL-33 resulted in less infiltration of neutrophils and monocytes into the lungs in association with lower circulating, lung and liver cytokine levels as well as reduced lung injury at 6 h after sepsis. IL-33 was required for the upregulation of IL-5 in type 2 Innate Lymphoid Cells (ILC2), while IL-5 neutralization suppressed neutrophil and monocyte infiltration in the lungs during CLP sepsis. This reduction in leukocyte infiltration in IL-33-deficient mice was reversed by administration of recombinant IL-5. These results indicate that IL-33 plays a major role in the local inflammatory changes in the lung, in part, by regulating IL-5 and this axis contributes to lung injury early after the onset of sepsis.

Thrombocytopenia impairs host defense and hemostasis in sepsis. However, the mechanisms of how platelets regulate host defense are not fully understood. High-mobility group box 1 (HMGB1), a danger-associated molecular pattern protein, is released during infection and contributes to the pathogenesis of sepsis. Platelets express HMGB1, which is released on activation and has been shown to play a critical role in thrombosis, monocyte recruitment, and neutrophil extracellular trap (NET) production. However, the contribution of platelet HMGB1 to host defense is unknown. To determine the role of platelet HMGB1 in polymicrobial sepsis, platelet-specific HMGB1 knockout (HMGB1 platelet factor 4 [PF4]) mice were generated and were subjected to cecal ligation and puncture (CLP), a clinically relevant intra-abdominal sepsis model. Compared with HMGB1 Flox mice and wild-type (WT) mice, HMGB1 PF4 mice showed significantly higher bacterial loads in the peritoneum and blood, an exaggerated systemic inflammation response, and significantly greater mortality after CLP. Deletion of HMGB1 in platelets was associated with lower platelet-derived chemokines (PF4 and RANTES) in the peritoneal cavity, and a decrease of platelet-neutrophil interaction in the lung after CLP. In vitro, neutrophils cocultured with activated HMGB1 knockout platelets showed fewer platelet-neutrophil aggregates, reduced reactive oxygen species (ROS) burst as compared with control. Taken together, these data reveal an unrecognized role of platelet HMGB1 in the regulation of neutrophil recruitment and activation via modulation of platelet activation during sepsis.

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Venous thromboembolic (VTE) disease, consisting of deep venous thrombosis (DVT) and pulmonary embolism (PE) is a leading cause of morbidity and mortality. Current prophylactic measures are insufficient to prevent all occurrence in part due to an incomplete understanding of the underlying pathophysiology. Mounting evidence describes interplay between activation of the innate immune system and thrombus development. Recent work has demonstrated that platelet release of HMGB1 leads to increased microvascular complications following injury. Additionally, platelet HMGB1 was found to enhance DVT and increase the formation of neutrophil extracellular traps (NETs), although the role of HMGB1 induced NET release in thrombosis remains unexplored. Utilizing a transgenic mouse lacking HMGB1 specifically from platelets and megakaryocytes we now demonstrate the specific role of platelet-derived HMGB1 in acute and subacute/chronic venous thrombosis. Platelets account for the majority of circulating HMGB1 and HMGB1 deposition within the developing clot. The pro-thrombotic effect of platelet-derived HMGB1 is mediated through enhanced neutrophil recruitment, NET formation and specifically release of extracellular DNA during NET formation. Taken together, these data suggest that platelet HMGB1 mediated NET release is a primary regulator of DVT formation in mice.

Various cell populations expressing NK1.1 contribute to innate host defense and systemic inflammatory responses, but their role in hemorrhagic shock and trauma remains uncertain. NK1.1+ cells were depleted by i.p. administration of anti-NK1.1 (or isotype control) on two consecutive days, followed by hemorrhagic shock with resuscitation and peripheral tissue trauma (HS/T). The plasma levels of IL-6, MCP-1, alanine transaminase (ALT), and aspartate aminotransferase (AST) were measured at 6 and 24 h. Histology in liver and gut were examined at 6 and 24 h. The number of NK cells, NKT cells, neutrophils, and macrophages in liver, as well as intracellular staining for TNF-α, IFN-γ, and MCP-1 in liver cell populations were determined by flow cytometry. Control mice subjected to HS/T exhibited end organ damage manifested by marked increases in circulating ALT, AST, and MCP-1 levels, as well as histologic evidence of hepatic necrosis and gut injury. Although NK1.1+ cell–depleted mice exhibited a similar degree of organ damage as nondepleted animals at 6 h, NK1.1+ cell depletion resulted in marked suppression of both liver and gut injury by 24 h after HS/T. These findings indicate that NK1.1+ cells contribute to the persistence of inflammation leading to end organ damage in the liver and gut.

Background The immunosuppression and immune dysregulation that follows severe injury includes type 2 immune responses manifested by elevations in interleukin (IL) 4, IL5, and IL13 early after injury. We hypothesized that IL33, an alarmin released early after tissue injury and a known regulator of type 2 immunity, contributes to the early type 2 immune responses after systemic injury. Methods and findings Blunt trauma patients admitted to the trauma intensive care unit of a level I trauma center were enrolled in an observational study that included frequent blood sampling. Dynamic changes in IL33 and soluble suppression of tumorigenicity 2 (sST2) levels were measured in the plasma and correlated with levels of the type 2 cytokines and nosocomial infection. Based on the observations in humans, mechanistic experiments were designed in a mouse model of resuscitated hemorrhagic shock and tissue trauma (HS/T). These experiments utilized wild-type C57BL/6 mice, IL33-/- mice, B6.C3(Cg)-Rorasg/sg mice deficient in group 2 innate lymphoid cells (ILC2), and C57BL/6 wild-type mice treated with anti-IL5 antibody. Severely injured human blunt trauma patients (n = 472, average injury severity score [ISS] = 20.2) exhibited elevations in plasma IL33 levels upon admission and over time that correlated positively with increases in IL4, IL5, and IL13 (P < 0.0001). sST2 levels also increased after injury but in a delayed manner compared with IL33. The increases in IL33 and sST2 were significantly greater in patients that developed nosocomial infection and organ dysfunction than similarly injured patients that did not (P < 0.05). Mechanistic studies were carried out in a mouse model of HS/T that recapitulated the early increase in IL33 and delayed increase in sST2 in the plasma (P < 0.005). These studies identified a pathway where IL33 induces ILC2 activation in the lung within hours of HS/T. ILC2 IL5 up-regulation induces further IL5 expression by CXCR2+ lung neutrophils, culminating in early lung injury. The major limitations of this study are the descriptive nature of the human study component and the impact of the potential differences between human and mouse immune responses to polytrauma. Also, the studies performed did not permit us to make conclusions about the impact of IL33 on pulmonary function. Conclusions These results suggest that IL33 may initiate early detrimental type 2 immune responses after trauma through ILC2 regulation of neutrophil IL5 production. This IL33–ILC2–IL5–neutrophil axis defines a novel regulatory role for ILC2 in acute lung injury that could be targeted in trauma patients prone to early lung dysfunction., In a reverse translation study from a human cohort to a mouse trauma model, Timothy Billiar and colleagues investigate the factors mediating immune dysregulation after severe injury., Author summary Why was this study done? The factors that initiate immune dysregulation after severe injury, including the skewing of the immune system towards type 2 responses, are unknown. Our aim was to determine if interleukin (IL) 33, an alarmin released after tissue injury and a regulator of type 2 immunity, contributes to the early type 2 immune responses after systemic injury. What did the researchers do and find? We measured IL33 and its soluble receptor, soluble suppression of tumorigenicity 2 (sST2), an endogenous antagonist of IL33, in the blood of 472 multiply injured trauma patients. IL33 levels were already markedly elevated on the first blood draw after injury and correlated with increases in IL4, IL5, and IL13 as well as nosocomial infections. Reverse translation experiments using a mouse model of hemorrhagic shock and tissue trauma were carried out to understand the functional link between IL33 and the type 2 cytokine, IL5. IL33 was shown to activate a resident set of innate lymphocytes (group 2 innate lymphoid cells [ILC2]) in the lungs to produce IL5, further leading to neutrophil IL5 production. What do these findings mean? These findings demonstrate the utility of using reverse translation of observations made in humans into mechanistic experimental models that recapitulate key components of the clinical response. IL33 and one of its target cells, ILC2, are identified for the first time as regulators of the early type 2 immune responses after severe injury. The findings include a previously unsuspected role for ILC2 in the regulation of neutrophils and acute lung injury. The findings identify IL33, IL5, or their receptors as potential targets to block early lung injury after polytrauma.

Sepsis remains a major clinical problem with high morbidity and mortality. As new inflammatory mediators are characterized, it is important to understand their roles in sepsis. Interleukin 33 (IL-33) is a recently described member of the IL-1 family that is widely expressed in cells of barrier tissues. Upon tissue damage, IL-33 is released as an alarmin and activates various types of cells of both the innate and adaptive immune system through binding to the ST2/IL-1 receptor accessory protein complex. IL-33 has apparent pleiotropic functions in many disease models, with its actions strongly shaped by the local microenvironment. Recent studies have established a role for the IL-33-ST2 axis in the initiation and perpetuation of inflammation during endotoxemia, but its roles in sepsis appear to be organism and model dependent. In this review, we focus on the recent advances in understanding the role of the IL-33/ST2 axis in sepsis.

Background— Growing evidence indicates that the presence of toll-like receptor 4 (TLR4) on platelets is a key regulator of platelet number and function. Platelets exposed to TLR4 agonists may serve to activate other cells such as neutrophils and endothelial cells in sepsis and other inflammatory conditions. The functional significance of platelet TLR4 in hemorrhagic shock (HS), however, remains unexplored. Methods and Results— Using thromboelastography and platelet aggregometry, we demonstrate that platelet function is impaired in a mouse model of HS with resuscitation. Further analysis using cellular-specific TLR4 deletion in mice revealed that platelet TLR4 is essential for platelet activation and function in HS with resuscitation and that platelet TLR4 regulates the development of coagulopathy after hemorrhage and resuscitation. Transfusion of TLR4-negative platelets into mice resulted in protection from coagulopathy and restored platelet function. Additionally, platelet-specific TLR4 knockout mice were protected from lung and liver injury and exhibited a marked reduction in systemic inflammation as measured by circulating interleukin-6 after HS with resuscitation. Conclusions— We demonstrate for the first time that platelet TLR4 is an essential mediator of the inflammatory response as well as platelet activation and function in HS and resuscitation.

Chronic rejection is the primary cause of long-term failure of transplanted organs and is often viewed as an antibody-dependent process. Chronic rejection, however, is also observed in mice and humans with no detectable circulating alloantibodies, suggesting that antibody-independent pathways may also contribute to pathogenesis of transplant rejection. Here, we have provided direct evidence that chronic rejection of vascularized heart allografts occurs in the complete absence of antibodies, but requires the presence of B cells. Mice that were deficient for antibodies but not B cells experienced the same chronic allograft vasculopathy (CAV), which is a pathognomonic feature of chronic rejection, as WT mice; however, mice that were deficient for both B cells and antibodies were protected from CAV. B cells contributed to CAV by supporting splenic lymphoid architecture, T cell cytokine production, and infiltration of T cells into graft vessels. In chimeric mice, in which B cells were present but could not present antigen, both T cell responses and CAV were markedly reduced. These findings establish that chronic rejection can occur in the complete absence of antibodies and that B cells contribute to this process by supporting T cell responses through antigen presentation and maintenance of lymphoid architecture.

Toll-like receptors (TLRs) detect endogenous ligands released after trauma and contribute to the proinflammatory response to injury. Posttraumatic mortality correlates with the extent of the immunoinflammatory response to injury that is composed of a complex regulation of innate and adaptive immune responses. Although TLRs are known to modulate innate immune responses, their role in the suppression of lymphocyte responses following traumatic tissue injury is unclear.This study used a murine model of severe peripheral tissue injury, involving muscle crush injury and injection of fracture components, to evaluate the roles of TLR2, TLR4, and TLR9 in the early and delayed immunoinflammatory phenotype. Posttraumatic immune dysfunction was measured in our trauma model using the following parameters: ex vivo splenocyte proliferation, TH1 cytokine release, and iNOS (inducible nitric oxide synthase) induction within splenic myeloid-derived suppressor cells. Systemic inflammation and liver damage were determined by circulating interleukin 6 levels and hepatocellular injury.Suppression of splenocyte responses after injury was dependent on TLR4 and TLR9 signaling as was posttraumatic iNOS upregulation in splenic myeloid-derived suppressor cells. TLR2 was found to have only a partial role through contribution to inhibition of splenocyte proliferation. This study also reveals the involvement of TLR2 and TLR4 in the initial systemic inflammatory response to traumatic tissue injury; however, this response was found to be TLR9 independent.These findings demonstrate the previously unidentified role of TLR2, TLR4, and TLR9 in the T cell-associated immune dysfunction following traumatic tissue injury. Importantly, this study also illustrates that TLRs play differing and selective roles in both the initial proinflammatory response and adaptive immune response after trauma. Furthermore, results in TLR9-deficient mice establish that the upregulation of early proinflammatory markers do not always correlate with the extent of sustained immune dysfunction. This suggests potential for targeted therapies that could limit immune dysfunction through selective inhibition of receptor function following injury.

Successful engraftment of organ transplants has traditionally relied on preventing the activation of recipient (host) T cells. Once T-cell activation has occurred, however, stalling the rejection process becomes increasingly difficult, leading to graft failure. Here we demonstrate that graft-infiltrating, recipient (host) dendritic cells (DCs) play a key role in driving the rejection of transplanted organs by activated (effector) T cells. We show that donor DCs that accompany heart or kidney grafts are rapidly replaced by recipient DCs. The DCs originate from non-classical monocytes and form stable, cognate interactions with effector T cells in the graft. Eliminating recipient DCs reduces the proliferation and survival of graft-infiltrating T cells and abrogates ongoing rejection or rejection mediated by transferred effector T cells. Therefore, host DCs that infiltrate transplanted organs sustain the alloimmune response after T-cell activation has already occurred. Targeting these cells provides a means for preventing or treating rejection., Blocking T cell activation in organ transplantation is important to prevent rejection. Here the authors show that unconventional monocyte-derived host dendritic cells enter allogeneic grafts to amplify the T cell response outside lymph nodes.

Background. Memory T cells migrate to and reject transplanted organs without the need for priming in secondary lymphoid tissues, but the mechanisms by which they do so are not known. Here, we tested whether CXCR3, implicated in the homing of effector T cells to sites of infection, is critical for memory T-cell migration to vascularized allografts. Methods. CD4 and CD8 memory T cells were sorted from alloimmunized CXCR3 ―/― and wildtype B6 mice and cotransferred to congenic B6 recipients of BALB/c heart allografts. Graft-infiltrating T cells were quantitated 20 and 72 hr later by flow cytometry. Migration and allograft survival were also studied in splenectomized alymphoplastic (aly/aly) recipients, which lack secondary lymphoid tissues. Results. We found that polyclonal and antigen-specific memory T cells express high levels of CXCR3. No difference in migration of wildtype versus CXCR3 ―/― CD4 and CD8 memory T cells to allografts could be detected in wildtype or aly/aly hosts. In the latter, wildtype and CXCR3 ―/― memory T cells precipitated acute rejection at similar rates. Blocking CCR5, a chemokine receptor also upregulated on memory T cells, did not delay graft rejection mediated by CXCR3 ―/― memory T cells. Conclusions. CXCR3 is not critical for the migration of memory T cells to vascularized organ allografts. Blocking CXCR3 or CXCR3 and CCR5 does not delay acute rejection mediated by memory T cells. These findings suggest that the mechanisms of memory T cell-homing to transplanted organs may be distinct from those required for their migration to sites of infection.

B cells are recognized as effector cells in allograft rejection that are dependent upon T cell help to produce alloantibodies causing graft injury. It is not known if B cells can also help T cells differentiate into memory cells in the alloimmune response. We found that in B-cell-deficient hosts, differentiation of alloreactive T cells into effectors was intact whereas their development into memory T cells was impaired. To test if B cell help for T cells was required for their continued differentiation into memory T cells, activated T cells were sorted from alloimmunized mice and transferred either with or without B cells into naive adoptive hosts. Activated T cells cotransferred with B cells gave rise to more memory T cells than those transferred without B cells and upon recall, mediated accelerated rejection of skin allografts. Cotransfer of B cells led to increased memory T cells by enhancing activated CD4 T-cell proliferation and activated CD8 T-cell survival. These results indicate that B cells help alloreactive T-cell differentiation, proliferation and survival to generate optimal numbers of functional memory T cells.

The pathways that lead to the internalization of pathogens via phagocytosis remain incompletely understood. We now demonstrate a previously unrecognized role for the gap junction protein connexin43 (Cx43) in the regulation of phagocytosis by macrophages and in the host response to bacterial infection of the peritoneal cavity. Primary and cultured macrophages were found to express Cx43, which localized to the phagosome upon the internalization of IgG-opsonized particles. The inhibition of Cx43 using small interfering RNA or by obtaining macrophages from Cx43 heterozygous or knockout mice resulted in significantly impaired phagocytosis, while transfection of Cx43 into Fc-receptor expressing HeLa cells, which do not express endogenous Cx43, conferred the ability of these cells to undergo phagocytosis. Infection of macrophages with adenoviruses expressing wild-type Cx43 restored phagocytic ability in macrophages from Cx43 heterozygous or deficient mice, while infection with viruses that expressed mutant Cx43 had no effect. In understanding the mechanisms involved, Cx43 was required for RhoA-dependent actin cup formation under adherent particles, and transfection with constitutively active RhoA restored a phagocytic phenotype after Cx43 inactivation. Remarkably, mortality was significantly increased in a mouse model of bacterial peritonitis after Cx43 inhibition and in Cx43 heterozygous mice compared with untreated and wild-type counterparts. These findings reveal a novel role for Cx43 in the regulation of phagocytosis and rearrangement of the F-actin cytoskeleton, and they implicate Cx43 in the regulation of the host response to microbial infection.

Objective We have characterized a hematopoietic cell population isolated from murine bone marrow that can facilitate purified hematopoietic stem cell engraftment across fully allogeneic major histocompatibility complex barriers. These facilitating cells (FCs) are classically identified as CD8α + TCR − by flow cytometry. Prior work has demonstrated that FCs are comprised of a heterogeneous cell population with both lymphoid and myeloid phenotypes. The present investigation was designed to more precisely characterize these subsets in terms of both phenotype and developmental potential. Methods Using fluorescence-activated cell sorting analysis, freshly isolated FCs were characterized for phenotypic expression of various lymphocyte progenitor markers. The lymphopoietic potential of FCs was evaluated by culturing freshly isolated FCs on bone marrow stroma cells overexpressing notch ligand 1 (OP9-DL1). Transcripts specific to pTα and TCRα were quantitated by employing real-time reverse transcription polymerase chain reaction. Maturation of the T-cell receptor (TCR) on FCs was biochemically analyzed by immunoprecipitation. Result Freshly isolated FCs had significant expression of CD44 + CD25 − and CD44 + CD25 + phenotypes. A discrete subset of CD8 + CD4 + cells are also identified in the FC population, similar to the double-positive phase of thymocyte development. Of particular interest, FCs express pre-TCRα (pTα) mRNA and protein as demonstrated by reverse transcription polymerase chain reaction, intracellular staining and immunoprecipitation. FCs grown on OP9-DL1 with interleukin-7 and FMS-like tyrosine kinase 3 ligand can mature into CD44 − CD25 + , CD8 + CD4 + and CD8 + T cells. During this developmental process, expression of the 33-kDa pTα chain was replaced by a mature 40-kDa TCRα chain. Conclusion Taken together, these data demonstrate for the first time that the marrow-derived FC contains a T-cell progenitor population that closely resembles developing thymocytes.

To provide evidence that iNOS expression solely in leukocytes plays a role in postoperative ileus.Intestinal handling initiates a molecular and cellular muscularis inflammation that has been associated with iNOS expression and ileus. The specific cellular source of iNOS is a matter of speculation.Chimeric mice were constructed that selectively express the iNOS gene only in their leukocytes or only in their parenchymal cells by lethal radiation and reconstitution with reciprocal bone marrow. Mild intestinal manipulation was used to induce postoperative ileus.Intestinal manipulation caused a significant leukocyte extravasation into the muscularis of all groups. Postoperative iNOS mRNA expression was evident in iNOS and transplanted iNOS mice with iNOS bone marrow but not in iNOS animals. The loss of the iNOS gene in leukocytes of iNOS mice reduced iNOS mRNA expression by 59%. iNOS-deficient mice and iNOS animals with iNOS leukocytes presented with a significant improvement in postoperative intestinal transit and in vitro smooth muscle contractility, whereas the replacement with iNOS bone marrow in iNOS mice completely reversed this improvement.These results clearly show that iNOS expressed in leukocytes within the intestinal muscularis plays a major role in mediating smooth muscle dysfunction and subsequently postoperative ileus.

Endogenous ligands from damaged cells, so-called damage-associated molecular pattern molecules, can activate innate immunity via TLR4 signaling. Hepatic warm ischemia and reperfusion (I/R) injury and inflammation is largely TLR4 dependent. We produced TLR4 chimeric mice to assess whether the TLR4-dependent injury required TLR4 expression on liver parenchymal or nonparenchymal cells. Chimeric mice were produced by adoptive transfer of donor bone marrow cells into irradiated recipient animals using reciprocal combinations of TLR4 wild-type (WT; C3H/HeOuj) and TLR4 mutant (C3H/HeJ) mouse bone marrow. Wild-type chimeric mice bearing TLR4 mutant hemopoietic cells and TLR4 mutant mice transplanted with their own bone marrow-derived cells were protected from hepatic I/R and exhibited decreased JNK and NF-κB activation compared with WT chimeric mice transplanted with their own bone marrow. In contrast, TLR4 mutant mice transplanted with TLR4 WT bone marrow were not protected from liver I/R and demonstrated pronounced increases in JNK and NF-κB activation when compared with autochthonous transplanted mutant mice. In addition, depletion of phagocytes taking up gadolinium chloride failed to provide any additional protection to TLR4 mutant mice, but substantially reduced damage in WT mice after hepatic I/R. Together, these results demonstrate that TLR4 engagement on actively phagocytic nonparenchymal cells such as Kupffer cells is required for warm I/R-induced injury and inflammation in the liver.

Background On antigenic stimulation, CD4 T cells generally proliferate more readily than CD8 T cells. The purpose of the present experiments was to determine whether nitric oxide (NO) might differentially modulate CD4 vs. CD8 T-cell proliferation. Methods Various concentrations of C57BL/6 iNOS +/+ and -/- bone marrow (BM)-derived antigen presenting cells (APC) (obtained by culture in granulocyte-macrophage colony-stimulating factor [GM-CSF] and interleukin [IL]-4) were cultured with purified BALB/c CD4 or CD8 T cells. Results Proliferation of CD4 T cells was similar in the presence of both NO synthase (iNOS) +/+ and -/- APC, whereas CD8 T cell proliferation was inhibited at the higher concentrations of iNOS +/+ dendritic cells (DC), coincident with increased levels of NO in the culture supernatant. Analysis of cytokine levels revealed that more interferon (IFN)-gamma, a potent inducer of NO synthesis in many cell types, was present in CD8 T cell than in CD4 T-cell-APC cultures. Addition of IFN-gamma to CD4 T-cell-APC cultures resulted in induction of NO synthesis and inhibition of proliferation at higher levels of NO than that required to inhibit CD8 T cell proliferation. However, CD4 T-cell proliferation was moderately inhibited in the presence of lipopolysaccharide (LPS)-stimulated CD11c DC, coincident with production of IFN-gamma and induction of NO synthesis. Conclusions These findings indicate that CD8 T-cell proliferation can be inhibited by lesser amounts of APC-derived NO than is necessary to inhibit CD4 T cell proliferation. NO synthesis was not initiated in CD4 T cell-DC cultures unless costimulatory molecules were up-regulated and IFN-gamma was produced.

We investigated the effective mechanisms of donor-specific blood transfusion (DST) using a sponge matrix allograft animal model. Sponges were harvested on various days postgrafting, and both the sponge infiltrating cells and sponge exudate fluid (SEF) were collected. DST completely suppressed cytotoxic T lymphocyte activity throughout the postgrafting period. SEF *N = O concentration (measured as nitrite) in DST mice was significantly lower than in ST mice. Conversely, the amount of PGE2 in the SEF from DST mice was higher than in ST mice. L)ST may induce intragraft suppressor factors (such as PCE2), resulting in reduced immune activation with suppression of local immune response.

Host defense mechanisms preventing bacterial invasion are particularly important in the gastrointestinal tract, since most gram-negative infections originate from there. Intraepithelial lymphocytes (IEL) seem to play an important role in this immune surveillance of the intestine, although their function in sepsis is not fully understood. To evaluate the characteristics of IEL in sepsis, C57BL/6 mice received a non-lethal dose of LPS and IEL were harvested at various time points thereafter. Although IEL displayed no phenotypic changes after endotoxemia, they displayed enhanced cytolytic activity and increased proliferation after LPS injection In addition, IEL from septic mice showed enhanced gamma interferon (IFN-gamma) production after LPS administration. The production of IFN-gamma may have induced the increased intestinal NOS-2 mRNA expression which was observed after endotoxemia. In conclusion, endotoxemia leads to functional activation of IEL without phenotypic changes. The activation of IEL and the subsequently increased NOS-2 expression may be important mechanisms in maintaining the mucosal barrier after sublethal LPS challenge.

Previously, we showed that NO induces thymocyte apoptosis via acaspase-1-dependent mechanism [1]. In the present study,we investigated the role of heme oxygenase, catalase, bax, and p53 inthis process. The NO donor, S-nitroso-N-acetyl penicillamine (SNAP),induced DNA fragmentation in thymocytes in a time- andconcentration-dependent way. SNAP (100 μM) induced 50–60%apoptosis; higher doses did not increase the rate of apoptosissignificantly. SNAP decreased catalase and heme iron (Fe) levelswithout affecting superoxide dismutase, glutathione, or total Fe storesin thymocytes. SNAP significantly increased the expression of hemeoxygenase 1 (HSP-32), p53, and bax but notbcl-2. Treatment with the heme oxygenase inhibitor, tinprotoporphyrin IX inhibited SNAP-induced thymocyte apoptosis.Furthermore, thymocytes from p53 null mice were resistantto NO-induced apoptosis. Our data suggest that NO may induce itscytotoxic effects on thymocytes by modulating heme oxygenase andcatalase activity as well as up-regulating pro-apoptotic proteinsp53 and bax.

Background. Donor-specific blood transfusion (DST) may improve allograft survival in human and animal models, but the mechanisms for this graft protective effect are incompletely understood. The sponge matrix allograft model was used to determine if DST induces regulatory factors within the allograft. Methods. C57BL/6 (H.2 b ) recipients received donor-specific (DBA/2J, H.2 d ) or syngeneic (C67BL/6) blood 7 days before sponge matrix allograft (DBA/2J) implantation. Fourteen days postgrafting, the sponge infiltrating cells (SIC) were examined for cytotoxic T cell (CTL) and natural killer (NK) activity, and sponge exudate fluid (SEF) was assessed for nitric oxide (.N=O) and prostaglandin E 2 (PGE 2 ) content. Interleukin- (IL) 2, IL-4, IL-10, and interferon-y (IFN-y) production by SIC was also determined. Recipient splenocytes were simultaneously assessed for anti-donor cytotoxic and proliferative responses and .N=O production. Results. SIC from mice receiving syngeneic transfusions (ST) acquired both CTL and NK activity postgrafting, with maximal activity by day 14. DST suppressed both CTL and NK activity throughout the postgrafting period. Limiting dilution analysis (LDA) of SIC to determine precursor and native CTL frequency showed significantly lower responder cell frequency after DST compared with ST. SEF.N=O levels and SIC production of IL-2 and IFN-y in grafted DST mice were significantly lower than in grafted mice receiving ST. No significant amounts of IL-4 and very low levels of IL-10 were produced by SIC from grafted mice after either ST or DST. Conversely, PGE 2 content of sponge fluid and serum from DST mice was higher than in mice receiving ST. Antigen stimulated splenocyte proliferation and CTL development assessed by LDA were also inhibited by DST. Conclusions. Reduction in local TH1 cytokines, absence of detectable TH2 cytokines, with enhanced PGE2 and depressed .N=O were observed in the local graft environment after DST. These data support the hypothesis that DST induces donor-specific intragraft suppressor factors, accompanied by reduced local and systemic immune activation.

To examine the effect of increased hexosamine flux in liver, the rate-limiting enzyme in hexosamine biosynthesis (glutamine:fructose-6-phosphate amidotransferase [GFA]) was overexpressed in transgenic mice using the PEPCK promoter. Liver from random-fed transgenic mice had 1.6-fold higher GFA activity compared with nontransgenic control littermates (276 +/- 24 pmol x mg(-1) x min(-1) in transgenic mice vs. 176 +/- 18 pmol x mg(-1) x min(-1) in controls, P < 0.05) and higher levels of the hexosamine end product UDP-N-acetyl glucosamine (288 +/- 11 pmol/g in transgenic mice vs. 233 +/- 10 pmol/g in controls, P < 0.001). Younger transgenic mice compared with control mice had lower fasting serum glucose (4.8 +/- 0.5 mmol/l in transgenic mice vs. 6.5 +/- 0.8 mmol/l in controls, P < 0.05) without higher insulin levels (48.0 +/- 7.8 pmol/l in transgenic mice vs. 56.4 +/- 5.4 pmol/l in controls, P = NS); insulin levels were significantly lower in transgenic males (P < 0.05). At 6 months of age, transgenic animals had normal insulin sensitivity by the hyperinsulinemic clamp technique. Hepatic glycogen content was higher in the transgenic mice (108.6 +/- 5.2 pmol/g in transgenic mice vs. 32.8 +/- 1.3 micromol/g in controls, P < 0.01), associated with an inappropriate activation of glycogen synthase. Serum levels of free fatty acids (FFAs) and triglycerides were also elevated (FFAs, 0.67 +/- 0.03 mmol/l in transgenic mice vs. 0.14 +/- 0.01 in controls; triglycerides, 1.34 +/- 0.15 mmol/l in transgenic mice vs. 0.38 +/- 0.01 in controls, P < 0.01). Older transgenic mice became heavier than control mice and exhibited relative glucose intolerance and insulin resistance. The glucose disposal rate at 8 months of age was 154 +/- 5 mg x kg(-1) x min(-1) in transgenic mice vs. 191 +/- 6 mg x kg(-1) x min(-1) in controls (P < 0.05). We conclude that hexosamines are mediators of glucose sensing for the regulation of hepatic glycogen and lipid metabolism. Increased hexosamine flux in the liver signals a shift toward fuel storage, resulting ultimately in obesity and insulin resistance.

Immature dendritic cells (DCs) are deficient in surface co-stimulatory molecules and have been shown to exhibit a 'tolerogenic' potential. We investigated the allostimulatory activity of immature DCs in one-way mixed leukocyte reactions and their capacity to inhibit anti-donor cytolytic activity in the sponge matrix allograft model. Immature DCs (CD80 and CD86 deficient) were derived from bone marrow cells propagated in GM-CSF and TGF-beta1. Mature DCs (CD80+ and CD86+) were derived from bone marrow cells propagated in GM-CSF and IL-4. Either 2 x 10(6) DBA/2J (DBA, H-2d) immature DCs or 2 x 10(6) mature DCs were injected intravenously into C57BL/6J (B6, H-2b) mice 7 days prior to sponge matrix allograft implantation. On day 12, the sponge was harvested and the graft-infiltrating cells were tested in vitro for cytotoxic T lymphocyte (CTL) activity. Immature dendritic cell (DC) infused significantly and markedly inhibited intra-graft CTL activity compared to mature DCs and syngeneic bone marrow control cells. The administration of immature DCs directly into the sponge allograft failed to induce hyporeactivity. Thus, the only systemic infusion of immature donor DCs was able to recapitulate the donor-specific transfusion effect, and the capacity of donor bone marrow cells to induce donor-specific hyporeactivity in the sponge allograft model.

Background. Increased nitric oxide (NO) production may contribute to intestinal barrier dysfunction and increased bacterial translocation (BT). Since BT may play a major role in graft-versus-host disease (GVHD) after small bowel transplantation (SBTx), we evaluated the role of NO production in GVHD after SBTX in the rat. Methods. Using the standard model of semiallogeneic SBTx in the rat, we prepared three experimental groups. Recipients in group 1 received LBNF 1 -LBNF 1 transplants and were treated with aminoguanidine (AG) (200 mg/kg), recipients in group 2 received Lewis-LBNF 1 grafts and were injected with saline, and recipients in group 3 received Lewis-LBNF 1 transplants and AG (200 mg/kg). Urine nitrite/nitrate levels were measured daily, and BT was determined by culturing peritoneal swabs, mesenteric lymph nodes, spleen, liver, and blood. Results. In group 1 we detected indefinite survival with normal histology. In group 2 a survival of 10.5±1.1 days was reached, and the typical histological features of acute GVHD were observed. The animals in group 3 showed a mean survival of 14.8±0.6 days (P

The study of mucosal immunity has revealed that complex reciprocal interactions occur between intestinal intraepithelial lymphocytes (IEL) and intestinal epithelial cells (IEC). The present study focuses on the induction of inducible nitric oxide (NO) synthase in cocultures of freshly isolated rat IEL and the rat epithelial cell line IEC-18 after the addition of interleukin-1beta (IL-1beta), tumor necrosis factor-alpha, or lipopolysaccharide. When IEL and IEC were separated using Transwell chambers, NO synthesis was not induced, indicating that cell-cell contact was required. Culture of IEC-18 with IEL, even in the absence of inflammatory stimuli such as IL-1beta, resulted in upregulation of class I and II antigens on IEC-18, due to the interferon-gamma (IFN-gamma) that is constitutively produced by IEL. Addition of anti-IFN-gamma antibody to the NO-producing cocultures resulted in inhibition of NO synthesis as well as the upregulation of class I and II antigen expression. These data indicate that IFN-gamma production by IEL conditions IEC for the expression of other components of the inflammatory process.

Aquatic larvae of the midge, Chironomus tentans, synthesize a 185-kDa silk protein (sp185) with the cysteine-containing motif Cys-X-Cys-X-Cys (where X is any residue) every 20-28 residues. We report here the cloning and full-length sequence of cDNAs encoding homologous silk proteins from Chironomus pallidivittatus (sp185) and Chironomus thummi (sp220). Deduced amino acid sequences reveal proteins of nearly identical mass composed of 72 blocks of 20-28 residues, 61% of which can be described by the motif X5-8-Cys-X5-(Trp/Phe/Tyr)-X4-Cys-X-Cys-X-Cys. Spatial arrangement of these residues is preserved more than surrounding sequences. cDNA clones enabled us to map the genes on polytene chromosomes and identify for the first time the homolog of the Camptochironomus Balbiani ring 3 locus in Chironomus thummi. The apparent molecular weight difference between these proteins (185 vs 220 kDa) is not attributable to primary structure and may be due to differential N-linked glycosylation. DNA distances and codon substitutions indicate that the C. tentans and C. pallidivittatus genes are more related to each other than either is to C. thummi; however, substitution rates for the 5'- and 3'-halves of these genes are different. Blockwise sequence comparisons suggest intragenic variation in that some regions evolved slower or faster than the mean and may have been subjected to different selective pressures.

We have previously demonstrated that administration of the nitric oxide (NO) synthesis inhibitor aminoguanidine (AG) to mice undergoing nonlethal graft-versus-host disease (GVHD) results in less destruction of host tissue and enhanced proliferative responses of splenic lymphocytes. Subsequently, we have determined whether the amelioration of GVHD pathology associated with inhibition of NO synthesis affects survival in a lethal GVHD model. Utilizing a C57BL/6 to C57BL/6xDBA2JF1 model, administration of parental lymph node lymphocytes instead of splenocytes results in 80-90% lethality by week 4 after GVHD induction. Administration of AG resulted in significantly decreased lethality coincident with decreased serum NO2- + NO3- levels. AG therapy had no effect on donor anti-host cytolytic T cell activity, which indicates that destruction of host tissue via this pathway was unaffected by the therapy. Histological evaluation of spleen, small intestine, bone, and mesenteric lymph node did not reveal any difference in the histological correlates of disease in the treated mice. AG increased various hematopoietic indices, including red blood cell count, white blood cell count, and hemoglobin, which indicates that the disruption of hematopoiesis during acute GVHD is mediated in part by NO. In addition, the number of GVHD mice with endogenous bacterial infections in the spleen and liver was significantly decreased in mice receiving AG therapy. These data indicate that NO plays a detrimental role during GVHD that appears to result in decreased hematopoietic indices and concomitant susceptibility to bacterial infection.

The migration of effector or memory T cells to the graft is a critical event in the rejection of transplanted organs. The prevailing view is that the key steps involved in T cell migration - integrin-mediated firm adhesion followed by transendothelial migration - are dependent on the activation of Gαi-coupled chemokine receptors on T cells. In contrast to this view, we demonstrated in vivo that cognate antigen was necessary for the firm adhesion and transendothelial migration of CD8+ effector T cells specific to graft antigens and that both steps occurred independent of Gαi signaling. Presentation of cognate antigen by either graft endothelial cells or bone marrow-derived APCs that extend into the capillary lumen was sufficient for T cell migration. The adhesion and transmigration of antigen-nonspecific (bystander) effector T cells, on the other hand, remained dependent on Gαi, but required the presence of antigen-specific effector T cells. These findings underscore the primary role of cognate antigen presented by either endothelial cells or bone marrow-derived APCs in the migration of T cells across endothelial barriers and have important implications for the prevention and treatment of graft rejection.

Dendritic cells (DC) are the most potent known antigen presenting cells, and play important roles both in immunity and tolerance induction. Nitric oxide (NO) is an important effector molecule that is involved in numerous aspects of the immune response. There have been no accounts to date of efforts to determine NO generation by well-characterized DC. In this report we describe the production of NO by highly purified DEC 205+ DC propagated from mouse bone marrow in response to granulocyte/macrophage-colony stimulating factor (GM-CSF) + interleukin-4 (IL-4). NO synthesis was induced in DC by interferon-gamma (IFN-gamma) and lipopolysaccharide (LPS), and was blocked by the inhibitor of nitric oxide synthase (NOS), NG-monomethyl-L-arginine (NMMA). Both "mature" B7-2+ (CD86+) DC and B7-2- (CD86-) DC progenitors could be induced to release NO. NO was also recovered from the supernatants of primary mixed leukocyte cultures containing comparatively high concentrations of B7-2+ DC in relation to purified allogeneic T cells. Furthermore, inhibition of NO release in these cultures by NMMA resulted in an increase in T cell proliferation. These observations suggest that NO may be an important soluble mediator of the interaction between DC and activated T cells. In addition to its ability to inhibit T cell proliferation, NO was also shown to induce programmed cell death in DC. This was visualized by the detection of DNA strand breaks with in situ nick translation. The percentage of DC apoptosis correlated with the level of NO in the cultures. Apoptosis was inhibited by the addition of NMMA. These results indicate that DC have the capacity both to stimulate and potentially limit the same allogeneic T cell response, in accordance with their production of NO.

Our previous work detailing the antiproliferative effects of nitric oxide (NO) in various assays of lymphocyte function in vitro led us to examine whether this immunosuppressive effect was also operative in vivo. The efficacy of administration of the NO synthesis inhibitor, aminoguanidine (AG), by various routes was examined. Oral administration as a 1% solution in the drinking water effectively lowered serum NO-2 + NO-3 levels. The effect of AG administration on cytolytic T-lymphocyte (CTL) development in vivo using the sponge matrix allograft model in both rats and mice was examined. Perhaps due to the small amount of NO produced at the graft site, AG administration did not affect CTL activity recovered from the grafts. In a nonlethal model of GvHD, oral administration of AG resulted in a decrease in destruction of host cells that was not associated with any differences in donor antihost CTL activity recovered from the spleens of these mice. Additionally, the proliferative response of T lymphocytes recovered from the spleens of AG-treated GvHD mice was greatly enhanced compared to the response of GvHD mice that did not receive AG. These results indicate that inhibition of NO does not potentiate CTL generation in vivo, which is in contrast to the results that we have seen in vitro. However, NO seems to induce bystander tissue injury in the GvHD process that may account for some host tissue destruction as well as the decreased T-lymphocyte proliferative responses characteristic of the GvHD disease process.

Chironomid salivary glands contain 40 cells dedicated to the synthesis of a relatively small ensemble of silk proteins. Glands in some species contain a special lobe composed of 4 cells distinguishable from the others. We have cloned a special lobe-specific cDNA from Chironomus thummi salivary glands. Northern blots of salivary gland RNA demonstrated that the cDNA hybridizes to a 2.5-kilobase transcript present only in the special lobe. In situ hybridization mapped the gene encoding this cDNA to region A2b on polytene chromosome IV, the locus of the special lobe-specific Balbiani ring a. The deduced amino acid sequence encodes a protein with a calculated molecular mass of 77 kDa and numerous potential glycosylation sites; it appears unrelated to other known chironomid silk proteins. Polyclonal antibody, raised against a cDNA-encoded fusion protein, reacted exclusively with a special lobe-specific 160-kDa silk protein. Lectin binding studies indicate that the immunoreactive 160-kDa protein contains both N- and O-linked glycan moieties. We conclude that glycosylation most likely contributes to the difference between calculated and apparent molecular masses and that this cDNA encodes the special lobe-specific silk protein previously described as ssp160 (Kolesnikov, N. N., Karakin, E. I., Sebeleva, T. E., Meyer, L., and Serfling, E.(1981) Chromosoma 83, 661-677).

The suppressed lymphocyte proliferative responses characteristic of graft-versus-host disease (GVHD) are due, in part, to production of nitric oxide (NO). In order to more fully elucidate the role of NO during GVHD, an NO synthesis inhibitor, aminoguanidine (AG), was administered to unirradiated (C57BL/6JxDBA/2J)F 1 mice injected with 5x10 7 C57BL/6J splenocytes. Administration of AG resulted in abrogation of the elevation in serum NO 2 - +NO 3 - levels characteristic of GVHD. A significantly increased percentage of splenocytes of host phenotype (H2 b/d , B220 + , and THY1.2 + ) and a significantly higher hematocrit value were detected in GVHD animals receiving AG therapy. Additionally, the Con A-induced proliferative response of splenocytes obtained from GVHD mice receiving AG therapy was increased compared with the responses of splenocytes from animals that did not receive AG therapy. Parameters not affected by AG therapy included NO synthesis by recovered peritoneal macrophages, donor antihost cytolytic activity in splenocyte populations, serum GM-CSF levels and long-term engraftment of donor cells. These data indicate that NO may play a role in the destruction of both lymphoid and erythroid host tissue as well as the reduced lymphoproliferative responses associated with the acute phase of GVHD.

While the pathological characteristics of acute graft versus host disease (GvHD) have been defined for many target organs, little attention has been paid to the functional changes of lymphocytes in target organs such as the liver and small intestine. We have shown previously, utilizing a nonlethal parent (C57BL/6J) into the F 1 (C57BL/6J × DBA2J F 1 ) GvHD model, that the intestinal mucosa is infiltrated exclusively by donor T cells with a CD8+ phenotype during the first 3 weeks post-GvHD induction. The present study investigated the functional changes associated with the phenotypic changes of intestinal intraepithelial lymphocytes (IEL) during the acute phase of GvHD. IEL displayed specific anti-host cytolytic activity during the second and third week after GvHD induction. In addition, enhanced cytolytic activity, detected in the presence of anti-CD3 antibody, was apparent during the second through fourth week, with a peak in the third week after GvHD induction. The IEL also showed enhanced proliferative responses to immobilized anti-CD3 during the first 2 weeks of acute GvHD, while profound inhibition of proliferation was observed in the splenocyte population of the same animals. During weeks 2 and 3 post-GvHD induction, the V β distribution of host IEL remained unchanged while the V β distribution of infiltrating donor CD8 + cells resembled that of the donor IEL population. In the small intestine, the increased cytolytic and proliferative activity of IEL during the course of the disease may provide a rationale for the involvement of this organ in the pathology associated with GvHD.

Background. Because increased nitric oxide (NO) production during sepsis can be detrimental to the host, inhibition of NO synthesis by various antagonists has been proposed as a therapeutic option. However, none of these approaches has addressed the possible regulation of inducible NO synthesis (iNOS) by endogenous intracellular signaling mechanisms. The purpose of our study was to determine whether intracellular calcium ([Ca2+]i) regulates iNOS. Methods. The macrophage cell line RAW 264.7 cells stimulated to produce NO were cultured in the presence or absence of the calcium ionophore A23187, ionomycin, or the Ca2+-adenosine triphosphatase inhibitor thapsigargin. Supernatants and total cellular RNA were recovered for measurement of iNOS messenger RNA (Northern blot) and NO2− (stable end product of NO), respectively. Simultaneous measurement of [Ca2+]i was performed by fluorescence spectrophotometry. Results. The calcium ionophore A23187, ionomycin, and thapsigargin all produced a dose-dependent inhibition of NO end product and iNOS messenger RNA (confirmed by densitometry) with a simultaneous increase in [Ca2+]i, confirmed by fluorescence spectrophotometry. This could not be reversed by exogenous l -arginine and was not observed if these agents were added beyond 0 hours of culture. Conclusions. Although iNOS is traditionally viewed as calcium independent, these data clearly show that [Ca2+]i regulates iNOS messenger RNA induction and end product synthesis. Endogenous cellular second messenger may thus be important in autoregulation of NO synthesis. Alternatives to pharmacologic or antagonist inhibition of NO deserve further investigation.

One of the principal target organs during graft-versus-host disease (GvHD) is the intestinal epithelium, although the reasons for the preferential involvement of particular organs in this disease are not known. This study analyzed the subset distribution of donor and host lymphocytes in the small intestinal epithelium and the spleen during GvHD in a parent (C57BL/6J) into F1 (C57BL/6JxDBA2/J F1) model. While the donor cell population in the spleen consisted of B and T cells, the donor cell population in the intestine contained only T cells during the course of GvHD. These infiltrating donor cells resembled the host intraepithelial lymphocytes (IELs), which are predominantly CD8+ T cells. This subset distribution of donor cells in the intestinal epithelium was remarkable since they originated from a donor splenocyte population containing few CD8+ lymphocytes. In addition, although the injected donor splenic T cells were virtually all alpha/beta TCR+, several months after GvHD induction more than 30% of the donor cells in the intestine were gamma/delta TCR+, thereby resembling the host IELs not only in their expression of CD4 and CD8, but also in their TCR expression. In contrast, no gamma/delta TCR+ donor cells were detectable in the spleen of GvHD mice. The subset distribution of donor and host IELs remained constant throughout the disease, while in the spleen a decrease of both donor and host B cells and a temporary increase of both donor and host CD8+ cells was observed. These findings demonstrate that in a given target organ during GvHD the disease process affects both donor and host lymphoid populations. In addition the different tissue microenvironments eventually lead to donor cell repopulation with a subset distribution similar to the host natural lymphoid population of the particular target organ.

Trauma results in a persistent depression in adaptive immunity, which contributes to patient morbidity and mortality. This state of immune paralysis following trauma is characterized by a change in cell-mediated immunity, specifically a depression in T-cell function and a shift toward TH2 T-cell phenotype. Upregulation of inducible nitric oxide synthase (iNOS) is well recognized after injury and contributes to the inflammatory response and organ damage early after trauma. However, it is unknown whether iNOS plays a role in adaptive immune dysfunction after trauma. This study utilized a murine model of severe peripheral tissue injury to show that iNOS is rapidly upregulated in macrophages and a (Gr-1-CD11b) myeloid-derived suppressor cell subpopulation in the spleen. Through the use of iNOS knockout mice, a specific iNOS inhibitor, and a nitric oxide (NO) scavenger, this study demonstrates that iNOS-derived NO is required for the depression in T-lymphocyte proliferation, interferon γ, and interleukin 2 production within the spleen at 48 h after trauma. These findings support the hypothesis that iNOS regulates immune suppression following trauma and suggest that targeting the sustained production of NO by iNOS may attenuate posttraumatic immune depression.

Inbreeding depression and lack of genetic diversity in inbred mice could mask unappreciated causes of graft failure or remove barriers to tolerance induction. To test these possibilities, we performed heart transplantation between outbred or inbred mice. Unlike untreated inbred mice in which all allografts were rejected acutely (6–16 days post-transplantation), untreated outbred mice had heterogeneous outcomes, with grafts failing early (75 days). Blocking T cell costimulation induced long-term graft acceptance in both inbred and outbred mice, but did not prevent the early graft failure observed in the latter. Further investigation of this early phenotype established that it is dependent on the donor, and not the recipient, being outbred and that it is characterized by hemorrhagic necrosis and neutrophilic vasculitis in the graft without pre-formed, high titer anti-donor antibodies in the recipient. Complement or neutrophil depletion prevented early failure of outbred grafts, whereas transplanting CD73-deficient inbred hearts, which are highly susceptible to ischemia-reperfusion injury, recapitulated the early phenotype. Therefore, outbred mice could provide broader insight into donor and recipient determinants of allograft outcomes but their hybrid vigor and genetic diversity do not constitute a uniform barrier to tolerance induction.

The aim of the study was to delineate the most optimal preservation conditions for small bowel grafts. Established preservation solutions such as EuroCollins, University of Wisconsin, histidine-tryptophane-ketoglutarate-Brettschneider, phosphate-buffered sucrose (PBS 140), and 3 new solutions--extracellular fluid (ECF), lactobionate fructose, and a modified lactobionate fructose solution--were compared with saline to determine the most optimal solution for the intestine. Recipient survival, standard histology, and glutaminase activity were used to assess the degree of injury encountered after 12 hr of preservation followed by transplantation. To evaluate the various preservation conditions, ECF was used at pH 6.8 (original ECF). Grafts were preserved most optimally when a vascular washout after the cold storage period was omitted and when topical rewarming of the graft with 37 degrees C saline before reperfusion was performed. Graft survival was not significantly different after preservation with any solution tested (50-83%). Highest graft survival (83%) was achieved with lactobionate fructose and PBS140. Histologic evaluation 20 min after reperfusion revealed minor differences between most groups; a slight advantage was observed for PBS140-preserved grafts. Mucosal glutaminase activity of PBS140-preserved grafts was significantly higher 20 min after reperfusion compared with any other solution evaluated, indicating a superior graft function. These data indicate that different preservation conditions have a great impact on postoperative graft survival and that PBS140 might be preferable to any of the other preservation solutions tested.

The main site of injury induced during small bowel preservation is perceived to be the basement membrane and the endothelium of the highly vascularized mucosa, an aspect evaluated here in further detail. The effects of preservation were studied using a specific basement membrane stain (laminin antibody), an endothelial cell stain (factor 8 antibody) and standard histology. In addition, mucosal glutaminase activity reflecting enterocyte integrity was measured as monitor of the extent of preservation injury. Using a rat model, small bowel grafts were harvested, the vascular bed and bowel lumen were flushed, and the grafts were stored (4 degrees C) for 1, 6, 9, and 12 hr and transplanted into syngeneic hosts. After cold storage prior to transplantation, full-thickness small bowel biopsies were obtained for the various tissue preparations. Histologic evaluation at the end of the preservation period revealed separation of the villous epithelium from the lamina propria that increased with extending preservation time. Tissue staining with the laminin antibody disclosed progressive changes with increasing preservation intervals. Staining with the factor 8 antibody demonstrated also progressive changes, but failed to reflect in a gradual fashion increasing endothelial cell injury. Histologic injury became more pronounced after transplantation and reperfusion, then showing destruction of epithelial cells; the extent of injury correlated with the duration of preservation. Glutaminase activity was maintained after cold storage, indicating that the enterocytes remained intact during this period, but when assayed after reperfusion, glutaminase decreased with increasing preservation intervals and increasing histologic mucosal damage. We conclude that cold ischemic injury involves primarily the endothelium and the basement membrane, which progresses to global mucosal impairment with reperfusion.

Acute graft-versus-host-disease is classically described as reactivity of donor lymphocytes to recipient alloantigens. To date there is debate as to whether GVHD can be induced across a species barrier. We recently reported the induction of stable xenogeneic chimerism (rat-->mouse) and donor-specific transplantation tolerance using the transplantation of untreated rat bone marrow cells into B10 mouse recipients. Survival of chimeras was excellent, and there was no evidence of GVHD. We now describe the induction of xenogeneic GVHD by transplanting large numbers of donor rat spleen cells with the bone marrow inoculum. All chimeras that received bone marrow and untreated spleen cells developed an external appearance compatible with GVHD and had a median survival time of 14 days. Mice that received equivalent numbers of untreated rat bone marrow alone appeared healthy, had no evidence for GVHD, and survived > 90 days. The usual epithelial target tissues for allogeneic GVHD in those mice that received xenogeneic bone marrow and spleen cells showed the presence of tissue injury and histologic features compatible with GVHD. Donor rat MHC class I and class II positive cells were prominent cell types present in the tongues of mice that developed features of GVHD, and this was accompanied by a significant inflammatory tissue response with loss of the dermal-epidermal architecture. In contrast, fully xenogeneic chimeras without GVHD had no evidence for tissue injury or pathologic cellular infiltrates when examined by immunohistochemical analysis. These data suggest that although fully xenogeneic chimeras resist GVHD, GVHD can be induced across a species barrier if sufficient numbers of donor rat spleen cells are added to the bone marrow inoculum. Further comparisons of these models may provide an approach to study the mechanisms responsible for xenoreactivity in vivo.

Reliable parameters reflecting the degree of graft injury after small bowel preservation are currently not established. We investigated hyaluronic acid (HA) and purine nucleoside phosphorylase (PNP) as indicators of preservation injury before small bowel transplantation. In the first part of the study, intestinal grafts were harvested, perfused with saline, and flushed either immediately or after 1, 6, 12, 24, and 48 hr of cold storage (n = 6/group). HA and PNP were assayed in vascular and luminal effluents. In the second part of the study, 24 grafts were transplanted after preservation periods of 1, 6, 9, and 12 hr (n = 6/group) to assess if HA and PNP are predictors of postoperative graft survival. HA levels in vascular effluents and PNP activities in luminal effluents correlated with duration of preservation time and predicted graft survival. Utilizing both parameters significantly increased the predictive accuracy.

The immunological status of Lewis (LEW) recipients of indefinitely surviving (greater than 400 days) orthotopic Brown-Norway (BN) small bowel allografts was investigated 1 to 1 1/2 years after cessation of immunosuppressive therapy with either cyclosporine or FK506 and compared with recipients of syngeneic grafts. A normal proliferative response (as measured by a mixed lymphocyte culture) of recipient peripheral lymph node lymphocytes in response to the donor-specific (BN) and the third-party (ACI) antigen, was observed in all experimental groups. Cytolytic T cell generation (as measured by a standard 51Cr-release cytotoxicity assay) in response to the donor-specific (BN) and the third-party (ACI) antigen was observed also in all groups. A FACS analysis of allograft-recipient splenocytes showed no evidence for systemic lymphoid chimerism. BN or ACI skin grafts transplanted onto recipients of allogeneic and syngeneic small bowel grafts were rejected completely in 12-17 days, while the intestinal grafts remained functional. Immunohistologic evaluation of the allografts, using anti-BN class I and anti-Lewis class II monoclonal antibodies showed anti-BN staining on the epithelial and endothelial structures, whereas the mononuclear cells in the lamina propria stained positively with the anti-LEW monoclonal antibody. However, lymphoid depletion and scarring of Peyer's patches and mesenteric lymph nodes as well as focal obliterative mesenteric arteriopathy, indicative of an indolent chronic rejection, were observed. These data demonstrate that recipients of indefinitely surviving small bowel allografts remain immune competent and do not retain the intestinal graft on the basis of specific hyporesponsiveness to the donor antigens.

Nitric oxide (NO) is a short-lived biologic mediator that is shown to be induced in various cell types and to cause many metabolic changes in target cells. Inhibition of tumor cell growth and antimicrobial activity has been attributed to the stimulation of the inducible type of the NO synthase (NOS). However, there is limited evidence for the existence of such inducible NOS in a human cell type. We show here the induction of NO biosynthesis in freshly isolated human hepatocytes (HC) after stimulation with interleukin 1, tumor necrosis factor (TNF), IFN-gamma, and endotoxin. Increased levels of nitrite (NO2-) and nitrate (NO3-) in culture supernatants were associated with NADPH-dependent NOS activity in the cell lysates. The production of NO2- and NO3- was inhibited by NG-monomethyl L-arginine and was associated with an increase in cyclic guanylate monophosphate release. The data presented here provide evidence for the existence of typical inducible NO biosynthesis in a human cell type.