Neutrophils mediate parenchymal tissue necrosis and accelerate the rejection of complete major histocompatibility complex-disparate cardiac allografts in the absence of interferon-gamma

Hypoxia inducible factor 2α promotes tolerogenic macrophage development during cardiac transplantation through transcriptional regulation of colony stimulating factor 1 receptor

Solid organ transplantation mobilizes myeloid cells, including monocytes and macrophages, which are central protagonists of allograft rejection. However, myeloid cells can also be functionally reprogrammed by perioperative costimulatory blockade to promote a state of transplantation tolerance. Transplantation tolerance holds promise to reduce complications from chronic immunosuppression and promote long-term survival in transplant recipients. We sought to identify different mediators of transplantation tolerance by performing single-cell RNA sequencing of acute rejecting or tolerized cardiac allografts. This led to the unbiased identification of the transcription factor, hypoxia inducible factor (HIF)-2α, in a subset of tolerogenic monocytes. Using flow cytometric analyses and mice with conditional loss or gain of function, we uncovered that myeloid cell expression of HIF-2α was required for costimulatory blockade-induced transplantation tolerance. While HIF-2α was dispensable for mobilization of tolerogenic monocytes, which were sourced in part from the spleen, it promoted the expression of colony stimulating factor 1 receptor (CSF1R). CSF1R mediates monocyte differentiation into tolerogenic macrophages and was found to be a direct transcriptional target of HIF-2α in splenic monocytes. Administration of the HIF stabilizer, roxadustat, within micelles to target myeloid cells, increased HIF-2α in splenic monocytes, which was associated with increased CSF1R expression and enhanced cardiac allograft survival. These data support further exploration of HIF-2α activation in myeloid cells as a therapeutic strategy for transplantation tolerance.

Neutrophils: New insights and open questions

Neutrophils are the first line of defense against bacteria and fungi and help combat parasites and viruses. They are necessary for mammalian life, and their failure to recover after myeloablation is fatal. Neutrophils are short-lived, effective killing machines. Their life span is significantly extended under infectious and inflammatory conditions. Neutrophils take their cues directly from the infectious organism, from tissue macrophages and other elements of the immune system. Here, we review how neutrophils traffic to sites of infection or tissue injury, how they trap and kill bacteria, how they shape innate and adaptive immune responses, and the pathophysiology of monogenic neutrophil disorders.

Interferon-γ converts human microvascular pericytes into negative regulators of alloimmunity through induction of indoleamine 2,3-dioxygenase 1

Early acute rejection of human allografts is mediated by circulating alloreactive host effector memory T cells (TEM). TEM infiltration typically occurs across graft postcapillary venules and involves sequential interactions with graft-derived endothelial cells (ECs) and pericytes (PCs). While the role of ECs in allograft rejection has been extensively studied, contributions of PCs to this process are largely unknown. This study aimed to characterize the effects and mechanisms of interactions between human PCs and allogeneic TEM. We report that unstimulated PCs, like ECs, can directly present alloantigen to TEM, but while IFN-γ-activated ECs (γ-ECs) show increased ability to stimulate alloreactive T cells, IFN-γ-activated PCs (γ-PCs) instead suppress TEM proliferation but not cytokine production or signaling. RNA sequencing analysis of PCs, γ-PCs, ECs, and γ-ECs reveal induction of indoleamine 2,3-dioxygenase 1 (IDO1) in γ-PCs to significantly higher levels than in γ-ECs that correlates with tryptophan depletion in vitro. Consistently, shRNA knockdown of IDO1 markedly reduces γ-PC-mediated immunoregulatory effects. Furthermore, human PCs express IDO1 in a skin allograft rejection humanized mouse model and in human renal allografts with acute T cell-mediated rejection. We conclude that immunosuppressive properties of human PCs are not intrinsic but instead result from IFN-γ-induced IDO1-mediated tryptophan depletion.

Cytokines affecting CD4+T regulatory cells in transplant tolerance. II. Interferon gamma (IFN-γ) promotes survival of alloantigen-specific CD4+T regulatory cells

CD4+T cells that transfer alloantigen-specific transplant tolerance are short lived in culture unless stimulated with specific-donor alloantigen and lymphocyte derived cytokines. Here, we examined if IFN-γ maintained survival of tolerance transferring CD4+T cells. Alloantigen-specific transplant tolerance was induced in DA rats with heterotopic adult PVG heart allografts by a short course of immunosuppression and these grafts functioned for >100days with no further immunosuppression. In previous studies, we found the CD4+T cells from tolerant rats that transfer tolerance to an irradiated DA host grafted with a PVG heart, lose their tolerance transferring ability after 3days of culture, either with or without donor alloantigen, and effect rejection of specific-donor grafts. If cultures with specific-donor alloantigen are supplemented by supernatant from ConA activated lymphocytes the tolerance transferring cells survive, suggesting these cells depend on cytokines for their survival. In this study, we found addition of rIFN-γ to MLC with specific-donor alloantigen maintained the capacity of tolerant CD4+T cells to transfer alloantigen-specific tolerance and their ability to suppress PVG allograft rejection mediated by co-administered naïve CD4+T cells. IFN-γ suppressed the in vitro proliferation of tolerant CD4+T cells. Tolerant CD4+CD25+T cells did not proliferate in MLC to PVG stimulator cells with no cytokine added, but did when IFN-γ was present. IFN-γ did not alter proliferation of tolerant CD4+CD25+T cells to third-party Lewis. Tolerant CD4+CD25+T cells' expression of IFN-γ receptor (IFNGR) was maintained in culture when IFN-γ was present. This study suggested that IFN-γ maintained tolerance mediating alloantigen-specific CD4+CD25+T cells.

The Inflammatory Cytokine IL-21 is Expressed by Splenic Neutrophils in Response to Transplantation of Allogeneic Cells

We have previously reported that GR-1 neutrophil/monocytes rose dramatically in the spleen, peaked by day 7 and declined through day 14. This period corresponded to the peak of acute Graft-Versus-Host Disease (aGVHD) in BALB/c mice transplanted with allogeneic donor cells. We now asked: what cytokines did these splenic neutrophil/monocytes express on day 7 and 14 post transplant? BALB/c mice were transplanted with allogeneic B6 or syngeneic BALB/c donor cells. Long term survival was recorded through day 31. Other groups were sacrificed on days 3, 5, 7, 14, 21 and 31 days post transplant to record the total number of cells in the spleens and their phenotypes. Neutrophils were isolated from the spleens of mice transplanted with B6 and BALB/c cells on days 7 and 14. Daily body weight demonstrated a transient drop in the syngeneic transplants on day 2 but a much greater drop with its nadir at day 7 and never fully recovering through 31 days. CD8/CD4 T lymphocytes peaked in the spleen on day 5 and were followed on day 7 by GR-I cells in all of the allogeneic transplants. In syngeneic transplants this early rise in lymphocytes did not occur and GR-1 cells peaked on day 14. Highly purified neutrophils were isolated in two separate experiments from the spleens on days 7 and 14 post transplant. In both experiments day 7 allogeneic neutrophils expressed significantly elevated levels of Interleukin-21 (IL-21) mRNA whereas the day 7 and 14 syngeneic cells expressed lower but significant levels of TNFα. Intracellular IL-21 was demonstrated in the allogeneic neutrophils on day 7 before and after in vitro stimulation. In conclusion Purified neutrophils isolated from the spleen on day 7, the early peak of allogeneic transplantation a GVHD, express high levels of IL-21 message and intracellular IL-21.

Peripheral Immune Cell Counts and Advanced Imaging as Biomarkers of Stroke Outcome

Introduction

Circulating neutrophil and lymphocyte levels may be modifiable outcome predictors of ischemic stroke. We sought to compare these immune cell parameters with advanced imaging assessment and the 90-day clinical outcome.

Methods

We used a retrospectively collected cohort of consecutive ischemic stroke patients presenting within 4.5 h of symptom onset who had acute CT perfusion and routine blood collection before treatment with intravenous thrombolysis and 24-hour MRI scanning at the John Hunter Hospital. Full blood counts were performed acutely at 24 h and 7 days. Patient outcomes were assed at 90 days after stroke with the modified Rankin Scale (mRS).

Results

Overall, 142 patients were assessed during the study period. Patients with a poor outcome (mRS 3-6) had increased neutrophils (44% increase, p = 0.016), decreased lymphocytes (7% decrease, p = 0.491) and an increased lymphocyte-to-neutrophil ratio (196% increase, p < 0.001). Patients with good outcomes (mRS 0-2) did not have significant changes in their full blood counts. There was no relationship between the neutrophil count at 24 h and penumbral volume (r² = 0.217, p = 0.212), reperfusion (r² = 0.111, p = 0.085), or core growth (r² = 0.297, p = 0.107). A backward multivariate analysis containing the 24-hour core volume and 24-hour neutrophil count was strongly related to the 3-month outcome (r² = 0.477, area under the curve = 0.902, p < 0.001).

Conclusions

Peripheral neutrophils have potential as a biomarker of outcome when used in conjunction with advanced imaging. Peripherally measured neutrophil counts change significantly over time after stroke and may be potential targets for immunomodulatory therapy in patients with a severe stroke or a large infarct volume.

Translational implications of endothelial cell dysfunction in association with chronic allograft rejection

Advances in therapeutics have dramatically improved short-term graft survival, but the incidence of chronic rejection has not changed in the past 20 years. New insights into mechanism are sorely needed at this time and it is hoped that the development of predictive biomarkers will pave the way for the emergence of preventative therapeutics. In this review, we discuss a paradigm suggesting that sequential changes within graft endothelial cells (EC) lead to an intragraft microenvironment that favors the development of chronic rejection. Key initial events include EC injury, activation and uncontrolled leukocyte-induced angiogenesis. We propose that all of these early changes in the microvasculature lead to abnormal blood flow patterns, local tissue hypoxia, and an associated overexpression of HIF-1α-inducible genes, including vascular endothelial growth factor. We also discuss how cell intrinsic regulators of mTOR-mediated signaling within EC are of critical importance in microvascular stability and may thus have a role in the inhibition of chronic rejection. Finally, we discuss recent findings indicating that miRNAs may regulate EC stability, and we review their potential as novel non-invasive biomarkers of allograft rejection. Overall, this review provides insights into molecular events, genes, and signals that promote chronic rejection and their potential as biomarkers that serve to support the future development of interruption therapeutics.

Graft microvascular disease in solid organ transplantation

Alloimmune inflammation damages the microvasculature of solid organ transplants during acute rejection. Although immunosuppressive drugs diminish the inflammatory response, they do not directly promote vascular repair. Repetitive microvascular injury with insufficient regeneration results in prolonged tissue hypoxia and fibrotic remodeling. While clinical studies show that a loss of the microvascular circulation precedes and may act as an initiating factor for the development of chronic rejection, preclinical studies demonstrate that improved microvascular perfusion during acute rejection delays and attenuates tissue fibrosis. Therefore, preservation of a functional microvasculature may represent an effective therapeutic strategy for preventing chronic rejection. Here, we review recent advances in our understanding of the role of the microvasculature in the long-term survival of transplanted solid organs. We also highlight microvessel-centered therapeutic strategies for prolonging the survival of solid organ transplants.

Effector mechanisms of rejection

Organ transplantation appears today to be the best alternative to replace the loss of vital organs induced by various diseases. Transplants can, however, also be rejected by the recipient. In this review, we provide an overview of the mechanisms and the cells/molecules involved in acute and chronic rejections. T cells and B cells mainly control the antigen-specific rejection and act either as effector, regulatory, or memory cells. On the other hand, nonspecific cells such as endothelial cells, NK cells, macrophages, or polymorphonuclear cells are also crucial actors of transplant rejection. Last, beyond cells, the high contribution of antibodies, chemokines, and complement molecules in graft rejection is discussed in this article. The understanding of the different components involved in graft rejection is essential as some of them are used in the clinic as biomarkers to detect and quantify the level of rejection.

Endogenous memory CD8 T cells are activated within cardiac allografts without mediating rejection

Endogenous memory CD8 T cells infiltrate MHC-mismatched cardiac allografts within 12-24 h posttransplant in mice and are activated to proliferate and produce IFN-γ. To more accurately assess the graft injury directly imposed by these endogenous memory CD8 T cells, we took advantage of the ability of anti-LFA-1 mAb given to allograft recipients on days 3 and 4 posttransplant to inhibit the generation of primary effector T cells. When compared to grafts from IgG-treated recipients on day 7 posttransplant, allografts from anti-LFA-1 mAb-treated recipients had increased numbers of CD8 T cells but these grafts had marked decreases in expression levels of mRNA encoding effector mediators associated with graft injury and decreases in donor-reactive CD8 T cells producing IFN-γ. Despite this decreased activity within the allograft, CD8 T cells in allografts from recipients treated with anti-LFA-1 mAb continued to proliferate up to day 7 posttransplant and did not upregulate expression of the exhaustion marker LAG-3 but did have decreased expression of ICOS. These results indicate that endogenous memory CD8 T cells infiltrate and proliferate in cardiac allografts in mice but do not express sufficient levels of functions to mediate overt graft injury and acute rejection.

The effects of in vivo B-cell depleting therapy on ex-vivo cytokine production

In renal transplantation, IL-17 production by T-cells might be dependent on the presence of B-cells. Therefore, the effect of in vivo B-cell depletion on ex-vivo IL-17 production was investigated. Twenty patients undergoing living-donor renal transplantation were recruited from a larger cohort of patients participating in a randomized, double-blind trial. All patients were allocated to a single intra-operative dose of either placebo or rituximab (375 mg/m(2)) added to the standard immunosuppressive therapy. Blood was collected at baseline, at one day, and at one month after surgery. The healthy kidney donors also gave blood at baseline. Peripheral blood mononuclear cells were stimulated ex-vivo in different manners (heat killed Candida albicans yeast, heat killed Staphylococcus aureus, or αCD3αCD28 coated beads), to address the role of B-cells in ex-vivo cytokine responses. The concentration of monocyte- and T-cell-derived cytokines (IL-1β, IL-6, TNF-α, IFN-γ, IL-17 and IL-22) was measured in supernatants. Of the 20 recruited patients, 13 received treatment with rituximab and 7 received placebo. In all patients, IL-17 was produced by CD4-positive, γδTCR-negative cells. After stimulation, there was no difference between patients and healthy controls in ex-vivo production of IL-17 or other cytokines. In all patients there was a general decrease of monocyte- and T-cell-derived cytokines after transplantation, except for IL-17. There was no difference between patients who received rituximab and patients who received placebo. A single dose of rituximab treatment added to standard immunosuppressive therapy in renal transplant patients did not influence the production of IL-17 or other monocyte- or T-cell derived cytokines after ex-vivo stimulation.

Allograft outcomes in outbred mice

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 posttransplantation), untreated outbred mice had heterogeneous outcomes, with grafts failing early (<4 days posttransplantation), acutely (6-24 days) or undergoing chronic rejection (>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 preformed, high titer antidonor 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.

Effects of immunosuppressive agents on Th17 cells involved in transplantation

The lymphocyte-derived helper T (Th) cells are critical regulators of the adaptive immune response and are associated with inflammatory disease. The most recently recognized Th-cell lineage, Th17, plays an important role in host defense against extracellular pathogens by secreting the proinflammatory cytokine, interleukin 17, and recruiting reactive oxygen species (ROS)-producing monocytes to the site of infection. However, accumulating evidence has implicated Th17-cell dysregulation as an underlying cause for some immune-related pathogenic conditions, including allograft rejection. Recent studies of human transplant patients have indicated that Th17 cells exhibit resistance to current immunosuppressive therapies that would otherwise prevent allograft rejection. In this review, we will discuss the most current research findings related to Th17-cell function in various kinds of allografts.

Interferon-gamma inhibits healing post scald burn injury

Impaired healing after severe burns remains a reason for prolonged hospitalization, opportunistic infections, and debilitating scarring. Interferon-gamma (IFN-γ) is an important immune regulator that has been shown to inhibit collagen synthesis by fibroblasts, resulting in delayed healing in incision wounds. To determine whether IFN-γ plays similar roles in the healing process after severe burn, we induced scald injury in mice deficient or sufficient in IFN-γ and examined local responses. In the absence of IFN-γ, scalded areas healed faster. This was associated with attenuated local inflammatory responses, enhanced reepithelialization, increased proliferation of keratinocytes in reepithelialized leading edges, and up-regulation of growth factors in burned skin areas. Furthermore, angiogenesis and myofibroblast formation commenced and terminated earlier in IFN-γ(-/-) mice compared with wild type (WT) controls. Our observations demonstrate that inhibition of IFN-γ results in accelerated healing after burn injury by dampening excessive inflammation and facilitating reepithelialization, collagen deposition, and wound contraction.

Potential role of γδ T cell-derived IL-17 in acute cardiac allograft rejection

BACKGROUND

Although αβ T cells are known to participate in the development of acute cardiac allograft rejection, the role of γδ T cells remains poorly understood. We hypothesized that γδ T cells contribute to acute allograft rejection thru interleukin (IL)-17 production.

METHODS

Donor hearts from FVB mice (H-2q) were heterotopically transplanted into C57BL/6-wild type (WT) and γδ T cell-deficient (TCRδ-/-) recipient mice (H-2b). Overall graft survival was monitored. Graft infiltrating cell profile, including γδ T cell subtype, cytokine expression, and myeloperoxidase activity were measured by flow cytometry, TaqMan (Applied Biosystems, Carlsbad, CA) polymerase chain reaction, and myeloperoxidase assay, respectively, on postoperative days 3 and 6.

RESULTS

Graft survival was prolonged in TCRδ-/- recipients compared with WT controls. Graft infiltrating cells, including CD45+, CD4+, CD8+, and Gr1+ cells were significantly decreased in TCRδ-/- recipients compared with WT. Donor hearts transplanted into TCRδ-/- recipients had reduced IL-17 and IL-6 messenger RNA expression. Corroborating the gene expression, intracellular cytokine staining showed decreased IL-17 producing cells in TCRδ-/- recipients. Finally, Vγ1+ and Vγ4+ T cells did not produce IL-17, although both represent 20% to 30% total graft infiltrating γδ T cells.

CONCLUSIONS

The γδ T cells promote acute cardiac allograft rejection, presumably by producing IL-17. The γδ T cell depletion may prove beneficial in prolonging allograft survival by suppressing IL-17 production.

Th17 cells induce a distinct graft rejection response that does not require IL-17A

IL-17A-producing helper T (Th17) cells have been implicated in the pathogenesis of autoimmune disease, inflammatory bowel disease and graft rejection, however the mechanisms by which they cause tissue damage remain ill-defined. We examined what damage Th17 cell lines could inflict on allogeneic skin grafts in the absence of other adaptive lymphocytes. CD4(+) Th17 cell lines were generated from two TCR transgenic mouse strains, A1(M).RAG1(-/-) and Marilyn, each monospecific for the male antigen Dby. After prolonged in vitro culture in polarizing conditions, Th17 lines produced high levels of IL-17A with inherently variable levels of interferon gamma (IFNγ) and these cells were able to maintain IL-17A expression following adoptive transfer into lymphopenic mice. When transferred into lymphopenic recipients of male skin grafts, Th17 lines elicited a damaging reaction within the graft associated with pathological findings of epidermal hyperplasia and neutrophil infiltration. Th17 cells could be found in the grafted skins and spleens of recipients and maintained their polarized phenotype both in vivo and after ex vivo restimulation. Antibody-mediated neutralization of IL-17A or IFNγ did not interfere with Th17-induced pathology, nor did it prevent neutrophil infiltration. In conclusion, tissue damage by Th17 cells does not require IL-17A.

Interleukin-17 Accelerates Allograft Rejection by Suppressing Regulatory T Cell Expansion

Background—

Interleukin-17 (IL-17), which is predominantly produced by T helper 17 cells distinct from T helper 1 or T helper 2 cells, participates in the pathogenesis of infectious, autoimmune, and allergic disorders. However, the precise role in allograft rejection remains uncertain. In the present study, we investigated the role of IL-17 in acute allograft rejection using IL-17-deficient mice.

Methods and Results—

Donor hearts from FVB mice were heterotopically transplanted into either C57BL/6J-IL-17-deficient (IL-17 − / − ) or -wild-type mice. Allograft survival was significantly prolonged in IL-17 − / − recipient mice due to reduced local inflammation accompanied by decreased inflammatory cell recruitment and cytokine/chemokine expression. IL-17 − / − recipient mice exhibited decreased IL-6 production and reciprocally enhanced regulatory T cell expansion, suggesting a contribution of regulatory T cells to prolonged allograft survival. Indeed, allografts transplanted into anti-CD25 mAb-treated IL-17 − / − recipient mice (regulatory T cell-depleted) developed acute rejection similar to wild-type recipient mice. Surprisingly, we found that gamma delta T cells rather than CD4 + and CD8 + T cells were key IL-17 producers in the allografts. In support, equivalent allograft rejection was observed in Rag-2 −/− recipient mice engrafted with either wild-type or IL-17 − / − CD4 + and CD8 + T cells. Finally, hearts transplanted into gamma delta T cell-deficient mice resulted in decreased allograft rejection compared with wild-type controls.

Conclusions—

During heart transplantation, (1) IL-17 is crucial for acceleration of acute rejection; (2) IL-17-deficiency enhances regulatory T cell expansion; and (3) gamma delta T cells rather than CD4 + and CD8 + T cells are a potential source of IL-17. IL-17 neutralization may provide a potential target for novel therapeutic treatment for cardiac allograft rejection.

Neutralization of mouse interleukin-17 bioactivity inhibits corneal allograft rejection

PURPOSE

To investigate the inhibitory effects of anti-mouse interleukin-17 (IL-17) monoclonal antibody (mAb) in high-responder corneal allograft rejection.

METHODS

C57BL/6 or BALB/c mice corneal grafts were grafted onto BALB/c hosts. The neutralizing mouse IL-17 antibody and isotype control were injected intraperitoneally immediately after transplantation for experimental treatment. At appropriate times after treatment, recipient grafts were assessed clinically and histologically, and recipient corneal graft- infiltrating cells were detected by immunohistochemistry and quantified by real-time PCR. The cytokine spleen levels of T helper type 1 (Th1), Th2, and Th17 were analyzed by enzyme-linked immunosorbent assay. Flow cytometric analysis was used to evaluate the frequencies of IL-17-producing Th17 cells.

RESULTS

Neutralization of IL-17 with anti-IL-17 mAb obviously prolonged allograft survival compared to the group that received isotype control. Neovascularizations and inflammatory immune cells in corneal stroma decreased in the allogeneic recipients treated with anti-IL-17 mAb. The mRNA (mRNA) level of graft-infiltrating cells, including neutrophiles, cluster of differentiation 4 (CD4) T cells, and CD8 T cells, decreased dramatically in the IL-17 neutralization group. At days 14 and 42, splenocytes from recipients treated with anti-IL-17 mAb produced significantly less of the pro-inflammatory cytokines interferon-gamma (IFN-γ), IL-12p40, and IL-17 compared to those from control Ig-treated recipients at day 14. However, Th2 cytokine IL-4 and IL-5 production increased, and IL-13 levels were not significantly different among the three groups. IL-6 production was elevated in recipients treated with anti-IL-17 mAb. Anti-IL-17 mAb reduced the percentage of Th17 in CD4+ T cells, but there was no statistical significance between anti-IL-17 mAb and the control group.

CONCLUSIONS

Neutralization of mouse IL-17 bioactivity with anti-IL-17 mAb improves allogeneic corneal graft survival and inhibits corneal allograft rejection to a certain extent by inhibiting production of graft-infiltrating inflammatory cells and decreasing the secretion of pro-inflammatory cytokines.

Interferon-γ influences the composition of leukocytic infiltrates in murine lyme carditis

Interferon (IFN)-γ is present in lesions of patients with Lyme disease and positively correlates with the severity of manifestations. To investigate the role of IFNγ in the development of Lyme carditis, wild-type and IFNγ-deficient C57BL/6 mice were infected with the causative bacterium, Borrelia burgdorferi. Histological analysis revealed no change in the severity of carditis between wild-type and IFNγ-deficient mice at 14, 21, 25, and 28 days after infection. However, a distinct shift in the types of leukocytes within the hearts of IFNγ-deficient mice was observed at 25 days. In the absence of IFNγ, the number of neutrophils in the heart was increased, whereas the number of T lymphocytes was decreased. Bacterial loads within hearts were the same as in wild-type mice. Macrophages secrete chemokines that recruit immune cells, which could contribute to the accumulation of leukocytes in murine Lyme carditis. The ability of IFNγ and B. burgdorferi to activate murine macrophages was examined, and the two stimuli synergistically induced chemoattractants for mononuclear cells (ie, CXCL9, CXCL10, CXCL11, CXCL16, and CCL12) and decreased those for neutrophils (ie, CXCL1, CXCL2, and CXCL3). IFNγ and B. burgdorferi also synergistically enhanced secretion of CXCL9 and CXCL10 by murine cardiac endothelial cells. These results indicate that IFNγ influences the composition of inflammatory infiltrates in Lyme carditis by promoting the accumulation of leukocytes associated with chronic inflammation and suppressing that of cells that typify acute inflammation.

Green tea epigallo-catechin-galleate ameliorates the development of obliterative airway disease

Lung transplantation has the worst outcome compared to all solid organ transplants due to chronic rejection known as obliterative bronchiolitis (OB). Pathogenesis of OB is a complex interplay of alloimmune-dependent and -independent factors, which leads to the development of inflammation, fibrosis, and airway obliteration that have been resistant to therapy. The alloimmune-independent inflammatory pathway has been the recent focus in the pathogenesis of rejection, suggesting that targeting this may offer therapeutic benefits. As a potent anti-inflammatory agent, epigallo-catechin-galleate (EGCG), a green tea catechin, has been very effective in ameliorating inflammation in a variety of diseases, providing the rationale for its use in this study in a murine heterotopic tracheal allograft model of OB. Mice treated with EGCG had reduced inflammation, with significantly less neutrophil and macrophage infiltration and significantly reduced fibrosis. On further investigation into the mechanisms, inflammatory cytokines keratinocyte (KC), interleukin-17 (IL-17), and tumor necrosis factor-α (TNF-α), involved in neutrophil recruitment, were reduced in the EGCG-treated mice. In addition, monocyte chemokine monocyte chemoattractant protein-1 (MCP-1) was significantly reduced by EGCG treatment. Antifibrotic cytokine interferon-γ-inducible protein-10 (IP-10) was increased and profibrotic cytokine transforming growth factor-β (TGF-β) was reduced, further characterizing the antifibrotic effects of EGCG. These findings suggest that EGCG has great potential in ameliorating the development of obliterative airway disease.

Th17: contributors to allograft rejection and a barrier to the induction of transplantation tolerance?

T helper (Th) type 17 cells are a recently described CD4 T-cell subset that may contribute to allograft rejection and act as a barrier to the induction of transplant tolerance. This review examines the involvement of Th17 cells in transplant rejection, how immunosuppressive medication may affect their induction and maintenance and the potential plasticity of developing Th17 cells. It also addresses the complex interplay between the Th17 and regulatory T-cell developmental pathways and the susceptibility of Th17 cells to regulation. Despite accumulating evidence, the precise impact of Th17 cells on transplant rejection and the induction of tolerance require further clarification.

High-risk corneal allografts and why they lose their immune privilege

PURPOSE OF REVIEW

Corneal allografts are routinely performed without HLA typing or systemic immunosuppressive drugs. However, certain conditions create high risks for immune rejection. This review discusses recent insights into the mechanisms that rob the corneal allograft of its immune privilege.

RECENT FINDINGS

Studies in mice have revealed that stimuli that induce new blood vessel growth in the cornea also elicit proliferation of lymph vessels. Lymph vessels facilitate migration of antigen-presenting cells to regional lymph nodes in which they induce alloimmune responses. The presence of blood vessels in the corneal graft bed creates a unique chemokine milieu that stimulates recruitment of sensitized lymphocytes into the corneal allograft. Other data indicate that although corneal allograft survival is closely associated with Foxp3 expression in CD4+CD25+Foxp3+ T regulatory cells (Tregs), reduced expression of Foxp3 in Tregs creates a high risk for graft rejection. Recent evidence indicates that allergic diseases have a profound impact on the immune response and produce a dramatic increase in corneal allograft rejection.

SUMMARY

Understanding the underlying mechanisms that create 'high-risk' hosts may provide important therapeutic targets for restoring immune privilege of corneal allografts and enhancing their survival.

T-cell alloimmunity and chronic allograft dysfunction

Solid organ transplantation is the standard treatment to improve both the quality of life and survival in patients with various end-stage organ diseases. The primary barrier against successful transplantation is recipient alloimmunity and the need to be maintained on immunosuppressive therapies with associated side effects. Despite such treatments in renal transplantation, after death with a functioning graft, chronic allograft dysfunction (CAD) is the most common cause of late allograft loss. Recipient recognition of donor histocompatibility antigens, via direct, indirect, and semidirect pathways, is critically dependent on the antigen-presenting cell (APC) and elicits effector responses dominated by recipient T cells. In allograft rejection, the engagement of recipient and donor cells results in recruitment of T-helper (Th) cells of the Th1 and Th17 lineage to the graft. In cases in which the alloresponse is dominated by regulatory T cells (Tregs), rejection can be prevented and the allograft tolerated with minimum or no immunosuppression. Here, we review the pathways of allorecognition that underlie CAD and the T-cell effector phenotypes elicited as part of the alloresponse. Future therapies including depletion of donor-reactive lymphocytes, costimulation blockade, negative vaccination using dendritic cell subtypes, and Treg therapy are inferred from an understanding of these mechanisms of allograft rejection.

High-mobility group box 1 promotes early acute allograft rejection by enhancing IL-6-dependent Th17 alloreactive response

Previously, we reported that extracellular high-mobility group box 1 (HMGB1) functions as an innate alarmin implicated in cardiac allograft acute rejection. We now present evidence suggesting that HMGB1 is pivotal in inducing interleukin-17 (IL-17)-producing alloreactive T cells by stimulating dendritic cells secretion of IL-6. Those IL-17(+) T cells are likely to be the major effector cells responsible for the early stage of cardiac allograft rejection through mediating an influx of neutrophils into allografts, and therefore, blockade of IL-17A significantly prolonged murine cardiac allograft survival. In contrast to the classical model for a dominant role of IFN-γ(+)-Th1 cells have in acute allograft rejection, our data suggest that IFN-γ(+)-Th1 cells are responsible for the late stage of graft destruction by inducing monocyte infiltration when IL-17(+) T-cell response recedes. Blockade of HMGB1 significantly decreased splenic alloreactive Th17 cells and IFN-γ-producing CD8(+) T cells in the recipients, leading to less infiltration of neutrophils along with lower IL-6 and IL-17 expression levels in the grafts as well as prolongation of cardiac allograft survival. Together, these data support a novel model in which HMGB1 induces IL-17-producing alloreactive T cells to mediate early stage of allograft rejection, whereas IFN-γ-producing alloreactive Th1 cells provoke graft destruction after Th17 response recedes.

Th17 promotes acute rejection following liver transplantation in rats

T help cell 17 (Th17), recently identified as a new subset of CD4(+) T cells, has been implicated in autoimmune diseases, tumor immunity, and transplant rejection. To investigate the role of Th17 in acute hepatic rejection, a rat model of allogeneic liver transplantation (Dark Agouti (DA) to Brown Norway (BN)) was established and isogeneic liver transplantation (BN to BN) was used as controls in the study. The expression of Th17-related cytokines in the liver and peripheral blood was determined by immunohistochemistry, flow cytometry, enzyme-linked immunosorbent assay (ELISA), or real-time quantitative reverse transcription polymerase chain reaction (RT-qPCR). Strong expression of interleukin-17A (IL-17A), IL-6, transforming growth factor-β (TGF-β), IL-8, and myeloperoxidase (MPO) was observed in liver allografts. The ratios of Th17 to CD4(+) lymphocytes in the liver and peripheral blood were dramatically increased in the allograft group compared with the control (P<0.01). Secreted IL-17 and IL-6 in liver homogenate and serum were significantly elevated in the allograft group, while secreted TGF-β was increased in liver homogenate and decreased in serum compared with the control (P<0.01). The messenger RNA (mRNA) levels of IL-17, IL-21, and IL-23 were enhanced in the allografts compared with the control (P<0.01). Correlation analysis showed significant correlations between IL-17 and IL-6 and TGF-β and between IL-17 and IL-21 and IL-23. The present study demonstrates that Th17 plays a role in promoting rat liver allograft rejection.

Interleukin-17 promotes early allograft inflammation

Acute cellular rejection of organ transplants is executed by donor-reactive T cells, which are dominated by interferon-gamma-producing cells. As interferon-gamma is dispensable for graft destruction, we evaluated the contribution of interleukin-17A (IL-17) to intragraft inflammation in major histocompatibility complex-mismatched heart transplants. A/J (H-2(a)) cardiac allografts placed into wild-type BALB/c (H-2(d)) mice induced intragraft IL-17 production on day 2 after transplant. Allografts placed into BALB/c IL-17(-/-) recipients demonstrated diminished production of the chemokines CXCL1 and CXCL2 and delayed neutrophil and T cell recruitment. However, by day 7 after transplant, allografts from IL-17(-/-) and wild-type recipients had comparable levels of cellular infiltration. The priming of donor-specific T cells was not affected by the absence of IL-17, and the kinetics of cardiac allograft rejection were similar in wild-type and IL-17(-/-) recipients. In contrast, IL-17(-/-) mice depleted of CD8 T cells rejected A/J allografts in a delayed fashion compared with CD8-depleted wild-type recipients. Although donor-reactive CD4 T cells were efficiently activated in both groups, the infiltration of effector T cells into allografts was impaired in IL-17(-/-) recipients. Our data indicate that locally produced IL-17 amplifies intragraft inflammation early after transplantation and promotes tissue injury by facilitating T cell recruitment into the graft. Targeting the IL-17 signaling network in conjunction with other graft-prolonging therapies may decrease this injury and improve the survival of transplanted organs.

Neutrophil mediated smooth muscle cell loss precedes allograft vasculopathy

BACKGROUND

Cardiac allograft vasculopathy (AV) is a pathological process of vascular remodeling leading to late graft loss following cardiac transplantation. While there is consensus that AV is alloimmune mediated, and evidence that the most important alloimmune target is medial smooth muscle cells (SMC), the role of the innate immune response in the initiation of this disease is still being elucidated. As ischemia reperfusion (IR) injury plays a pivotal role in the initiation of AV, we hypothesize that IR enhances the early innate response to cardiac allografts.

METHODS

Aortic transplants were performed between fully disparate mouse strains (C3H/HeJ and C57BL/6), in the presence of therapeutic levels of Cyclosporine A, as a model for cardiac AV. Neutrophils were depleted from some recipients using anti-PMN serum. Grafts were harvested at 1,2,3,5d and 1,2wk post-transplant. Ultrastructural integrity was examined by transmission electron microscopy. SMC and neutrophils were quantified from histological sections in a blinded manner.

RESULTS

Grafts exposed to cold ischemia, but not transplanted, showed no medial SMC loss and normal ultrastructural integrity. In comparison, allografts harvested 1d post-transplant exhibited > 90% loss of SMC (p < 0.0001). SMC partially recovered by 5d but a second loss of SMC was observed at 1wk. SMC loss at 1d and 1wk post-transplant correlated with neutrophil influx. SMC loss was significantly reduced in neutrophil depleted recipients (p < 0.01).

CONCLUSIONS

These novel data show that there is extensive damage to medial SMC at 1d post-transplant. By depleting neutrophils from recipients it was demonstrated that a portion of the SMC loss was mediated by neutrophils. These results provide evidence that IR activation of early innate events contributes to the etiology of AV.

Comparison of immunopathology and locomotor recovery in C57BL/6, BUB/BnJ, and NOD-SCID mice after contusion spinal cord injury

Studies of cell transplantation therapeutics in animal models of traumatic spinal cord injury (SCI) are often hampered by partial or complete rejection of the graft by the host. Pharmacological immunosuppression is rarely sufficient to prevent rejection. Further, the immunological niche created by both the host immune response and immunosuppressant drugs could hypothetically influence the proliferation, differentiation, and fate of transplanted progenitor/stem cells. To avoid these confounds, we have previously used the constitutively immunodeficient non-obese diabetic severe combined immunodeficient (NOD-SCID) mouse as a model for transplantation studies following SCI. In the current study, we compare behavioral and histological recovery in NOD-SCID, C57BL/6, and BUB/BnJ mice of both sexes to better facilitate interpretation of data from studies using NOD-SCID mice. Of the strains examined, NOD-SCID mice exhibited the greatest locomotor recovery in the open field; no sex differences were detected in locomotor recovery in any of the strains. Stereologic estimation of the number of infiltrated neutrophils showed more cells in C57BL/6 mice than NOD-SCID mice, with BUB/BnJ mice having an intermediate number. The volume of macrophages/microglia did not differ between strains or sexes, though more rostral-caudal spreading was observed in C57BL/6 and BUB/BnJ than NOD-SCID mice. No significant differences were detected in lesion volume. Taken together these findings demonstrate that relative to other strains, NOD-SCID mice have both similar primary lesion volume and cellular inflammatory parameters after SCI, and support the applicability of the model for neurotransplantation studies.

Recent progress and new perspectives in studying T cell responses to allografts

Studies in the past decade advanced our understanding of the development, execution and regulation of T-cell-mediated allograft rejection. This review outlines recent progress and focuses on three major areas of investigation that are likely to guide the development of graft-prolonging therapies in the future. The discussed topics include the contribution of recently discovered molecules to the activation and functions of alloreactive T cells, the emerging problem of alloreactive memory T cells and recently gained insights into the old question of transplantation tolerance.

Role of T cells in graft rejection and transplantation tolerance

Transplantation is the most effective treatment for end-stage organ failure, but organ survival is limited by immune rejection and the side effects of immunosuppressive regimens. T cells are central to the process of transplant rejection through allorecognition of foreign antigens leading to their activation, and the orchestration of an effector response that results in organ damage. Long-term transplant acceptance in the absence of immunosuppressive therapy remains the ultimate goal in the field of transplantation and many studies are exploring potential therapies. One promising cellular therapy is the use of regulatory T cells to induce a state of donor-specific tolerance to the transplant. This article first discusses the role of T cells in transplant rejection, with a focus on the mechanisms of allorecognition and the alloresponse. This is followed by a detailed review of the current progress in the field of regulatory T-cell therapy in transplantation and the translation of this therapy to the clinical setting.

Interleukin-17 and its expanding biological functions

Interleukin-17 (IL-17) and IL-17-producing cells have been shown to play important roles in inflammation and the immune response. IL-17 is believed to be mainly produced by T helper 17 (Th17) cells, a unique helper T-cell subset different from Th1 and Th2 cells. Other subsets of T cells such as gammadeltaT and natural killer T (NKT) cells have also been found to produce IL-17 in response to innate stimuli. IL-17 acts as a proinflammatory cytokine that can induce the release of certain chemokines, cytokines, matrix metalloproteinases (MMPs) and antimicrobial peptides from mesenchymal and myeloid cells. This leads to the expansion and accumulation of neutrophils in the innate immune system and links innate and adaptive immunity in vivo. Furthermore, increasing evidence indicates that IL-17 and IL-17-producing cells are involved in the pathogenesis of various diseases such as allergies, autoimmune diseases, allograft transplantation and even malignancy. They may also play protective roles in host defense against infectious diseases and promote induction of cytotoxic T lymphocyte (CTL) responses against cancer. Targeting of the IL-17 axis is under investigation for the treatment of inflammatory disorders.

MMP-8 promotes polymorphonuclear cell migration through collagen barriers in obliterative bronchiolitis

Increased levels of MMP-8 (neutrophil collagenase) have been reported in OB, but the biological role of MMP-8 in OB is not known. MMP-8 is an interstitial collagenase highly expressed by polymorphonuclear leukocytes, which are prominent in early OB. Here, we show that MMP-8 promotes migration of PMNs through the collagen-rich matrix in a mouse heterotopic airway transplant model of OB. Overall, MMP-8(-/-) mice had significantly fewer PMNs in the airway lumen 2 and 14 days post-transplantation, and the percentage of PMNs traversing the matrix to the lumen was decreased markedly in the MMP-8(-/-) compared with WT mice at 14 days. There were significantly more PMNs outside of the lumen in the ECM in the MMP-8(-/-) mice compared with WT mice. In vitro, significantly fewer MMP-8(-/-) PMNs migrated through 3D cross-linked collagen gels than WT PMNs. MMP inhibitor GM6001 was also able to impede migration of WT PMNs through collagen gels. The decreased migration was likely a result of pericollagenase activity of MMP-8, as WT PMNs expressing MMP-8 were not able to migrate effectively through collagen that was resistant to the collagenase. Protection from OB was seen in the MMP-8(-/-) mice, as the airway lumen had significantly less obliteration and collagen deposition, suggesting that MMP-8 plays an important role in the pathogenesis of OB.

Changes in the serum levels of interleukin-17/interleukin-23 during acute rejection in liver transplantation

Interleukin-23 (IL-23) and T helper 17 (Th17) cells have been cast as major players in autoimmunity, but their role in transplantation immunity remains to be specified. The aim of our study was to investigate the time course of serum levels of IL-23 and IL-17 during hepatic allograft rejection. Serum levels of IL-23 and IL-17 were determined in 20 healthy subjects and 50 hepatic transplant recipients. These patients were divided into 2 groups: group I was composed of 15 patients with acute rejection, and group II was composed of 35 patients without acute rejection. Samples were collected on days 1 and 7 after liver transplantation and on the day of liver biopsy. The concentrations of IL-23 were similar for the rejection group and nonrejection group at early postoperative times. We observed a significant increase in serum IL-23 levels in the rejection group when a diagnosis of acute rejection had been established. Similarly to IL-23, at the diagnosis of acute rejection, the concentration of IL-17 was significantly higher in the rejection group versus the nonrejection group. The whole transplant group, including those with stable graft function, had higher serum levels of IL-23 and IL-17 than the controls during the entire postoperative period. In conclusion, IL-23 and IL-17 are up-regulated during acute hepatic rejection. These findings suggest a role for Th17 cells in human liver allograft rejection.

CD8 T cells producing IL-17 and IFN-gamma initiate the innate immune response required for responses to antigen skin challenge

Effector CD8 T cell recruitment into the skin in response to Ag challenge requires prior CXCL1/KC-directed neutrophil infiltration. Mechanisms inducing CXCL1 production and the dynamics of neutrophil-CD8 T cell interactions during elicitation of Ag-specific responses in the skin were investigated. CXCL1 and CXCL2/MIP-2 were produced within 3-6 h of Ag challenge at 10-fold higher levels in skin challenge sites of Ag-sensitized vs nonsensitized mice. In the challenge sites of sensitized mice this production decreased at 6-9 h postchallenge to near the levels observed in skin challenge sites of nonsensitized mice but rose to a second peak 12 h after challenge. The elevated early neutrophil chemoattractant production at 3-6 h after skin challenge of sensitized animals required both IFN-gamma and IL-17, produced by distinct populations of Ag-primed CD8 T cells in response to Ag challenge. Although induced by the Ag-primed CD8 T cells, the early CXCL1 and CXCL2 production was accompanied by neutrophil but not CD8 T cell infiltration into the skin Ag challenge site. Infiltration of the CD8 T cells into the challenge site was not observed until 18-24 h after challenge. These results demonstrate an intricate series of early interactions between Ag-specific and innate immune components that regulate the sequential infiltration of neutrophils and then effector T cells into the skin to mediate an immune response.

Translating costimulation blockade to the clinic: lessons learned from three pathways

SUMMARY

As the recognition that costimulatory signals are critical for optimal T-cell activation, proliferation, and differentiation, there has been an explosion in the study of costimulatory molecules and their roles in enhancing anti-donor T-cell responses following transplantation. Here, we focus on the bench-to-beside translation of blocking agents designed to target three critical costimulatory pathways: the CD28/CD80/CD86 pathway, the CD154/CD40 pathway, and the lymphocyte function associated antigen-1/intercellular adhesion molecule pathway. While blockade of each of these pathways proved promising in inhibiting donor-reactive T-cell responses and promoting long-term graft survival in murine models of transplantation, the progression of development of therapeutic agents to block these pathways has each taken a slightly different course. Both logistical and biological pitfalls have accompanied the translation of blockers of all three pathways into clinically applicable therapies, and the development of costimulatory blockade as a substitute for current standard-of-care calcineurin inhibitors has by no means reached completion. Collaboration between both the basic and clinical arenas will further propel the development of costimulation blockers currently in the pipeline, as well as of novel methods to target these critical pathways during transplantation.

Interleukin 17-producing T helper cells in alloimmunity

Interleukin (IL) 17 is a proinflammatory cytokine already known to play a defense role against microbes and a pathogenic role in a number of autoimmune diseases. Although IL-17 can be produced by a variety of cells including neutrophils, CD8+, NK, and gamma-delta T cells, the concept of IL-17-secreting CD4+ T helper cells (Th17), distinct from Th1 and Th2, recently emerged. Herein, we discuss arguments in favor of a Th17-mediated alternative pathway of allograft rejection based on clinical and experimental observations drawn from the literature. We also discuss the complex interplays among regulatory T cells and Th17 cells in the allogeneic context.

IFN-gamma dictates allograft fate via opposing effects on the graft and on recipient CD8 T cell responses

CD8 T cells are necessary for costimulation blockade-resistant rejection. However, the mechanism by which CD8 T cells mediate rejection in the absence of major costimulatory signals is poorly understood. IFN-gamma promotes CD8 T cell-mediated immune responses, but IFN-gamma-deficient mice show early graft loss despite costimulation blockade. In contrast, we found that IFN-gamma receptor knockout mice show dramatically prolonged graft survival under costimulation blockade. To investigate this paradox, we addressed the effects of IFN-gamma on T cell alloresponses in vivo independent of the effects of IFN-gamma on graft survival. We identified a donor-specific CD8 T cell breakthrough response temporally correlated with costimulation blockade-resistant rejection. Neither IFN-gamma receptor knockout recipients nor IFN-gamma-deficient recipients showed a CD8 breakthrough response. Graft death on IFN-gamma-deficient recipients despite costimulation blockade could be explained by the lack of IFN-gamma available to act on the graft. Indeed, the presence of IFN-gamma was necessary for graft survival on IFN-gamma receptor knockout recipients, as either IFN-gamma neutralization or the lack of the IFN-gamma receptor on the graft precipitated early graft loss. Thus, IFN-gamma is required both for the recipient to mount a donor-specific CD8 T cell response under costimulation blockade as well as for the graft to survive after allotransplantation.

Recipient Immune Repertoire and Engraftment Site Influence the Immune Pathway Effecting Acute Hepatocellular Allograft Rejection

As novel acute allograft rejection mechanisms are being discovered, determining the conditions that promote or subvert these distinct rejection pathways is important to interpret the clinical relevance of these pathways for specific recipient groups as well as specific tissue and organ transplants. We have employed a versatile hepatocellular allograft model to analyze how the host immune repertoire and immune locale influences the phenotype of the rejection pathway. In addition, we investigated how peripheral monitoring of cellular and humoral immune parameters correlates with the activity of a specific rejection pathway. Complete MHC mismatched hepatocellular allografts were transplanted into immune competent CD4-deficient, CD8-deficient, or C57BL/6 hosts to focus on CD8-dependent, CD4-dependent, or combined CD4 and CD8-dependent alloimmunity, respectively. Hepatocellular allografts were transplanted to the liver or kidney subcapsular space to investigate the influence of the immune locale on each rejection pathway. The generation of donor-reactive DTH, alloantibody, and allospecific cytotoxicity was measured to assess both cellular and humoral immunity. Graft-infiltrating lymphocytes were phenotyped and enumerated in each recipient group. In the presence of CD8+ T cells, cytolytic cellular activity is the dominant mechanism of graft destruction and is amplified in the presence of CD4+ T cells. The absence of CD8+ T cells (CD8 KO) results in potent humoral immunity as reflected by high levels of cytotoxic alloantibody and graft rejection with similar kinetics. Transplant to the liver compared to the kidney site is distinguished by more rapid kinetics of rejection and alloimmunity, which is predominately cell mediated rather than a mix of both humoral and cell-mediated immunity. These studies define several rejection mechanisms occurring in distinct immune conditions, highlighting the plasticity of acute allograft rejection responses and the need to design specific monitoring strategies for these pathways to allow dynamic immune assessment of clinical transplant recipients and targeted immunotherapies.

Effect of CXCL-1/KC production in high risk vascularized corneal allografts on T cell recruitment and graft rejection

BACKGROUND

The survival rate of corneal allografts in high-risk vascularized corneal bed recipients is poor, similar to vascularized solid organ allografts. Although the early induction of selective chemokines in solid organs is required for the optimal recruitment of T cells into rejecting allografts, little is known about the role of these chemokines in high risk corneal allografts.

METHODS

Orthotopic corneal allotransplants were performed in low-risk (nonvascularized) and high-risk (vascularized) C57BL/6 (H-2b) recipients using Balb/c (H-2d) donors. Intragraft production of CXC chemokines was measured by Luminex and enzyme-linked immunosorbent assay on corneal transplant extracts at different times after surgery. Rabbit anti-KC serum was used to test its role in high risk corneal allograft survival.

RESULTS

Early upregulation of CXCL1/KC occurs 3 days after transplantation in high risk allograft only. Moreover, the T-cell chemoattractants, CXCL9/Mig and CXCL10/IP10, are produced late (day 10) after surgery and their production correlates with the recruitment of CD4 T cells into the graft. Furthermore, in vivo neutralization of CXCL1/KC with anti-KC sera results in increased graft survival and decreased recruitment of T cells into high-risk allografts.

CONCLUSION

We propose that a high risk vascularized cornea behaves like a vascularized solid organ transplant. The early production of CXCL1/KC is crucial to the induction of T-cell chemoattractants necessary for the recruitment of allospecific CD4 T cells into the graft. In vivo neutralization of CXCL1/KC represents a potential novel therapy that could be used to increase the survival rate of high-risk vascularized corneal allografts.

Interleukin-23 and TH17 cells in transplantation immunity: does 23+17 equal rejection?

Interleukin-23 (IL-23) and the recently discovered Th17 cells have been implicated in the pathogenesis of autoimmune diseases. This review will discuss current understanding of T-cell subsets in transplantation immunity and will explore the role of IL-23 and Th17 cells in allograft rejection, tolerance, and ischemia reperfusion injury.

Injection of lipopolysaccharide induces the migration of splenic neutrophils to the T cell area of the white pulp: role of CD14 and CXC chemokines

There is increasing evidence that neutrophils are involved in the regulation of adaptive immunity. We therefore tested whether these cells may colocalize with T lymphocytes in lymphoid organs. Our results demonstrate that administration of the microbial product LPS induces the migration of neutrophils in the spleen from the red pulp and the marginal zone to the area of the white pulp where T cells reside. This movement is CD14-dependent, whereas the recruitment of neutrophils in the peritoneal cavity is increased in the absence of CD14. Our data further suggest the involvement of the chemokine MIP-2 and keratinocyte-derived chemokine and their receptor CXCR2. We conclude that neutrophils may interact with naïve T cells upon infection/inflammation and that the migration of neutrophils in the lymphoid organs and in the periphery is regulated differently by a signal transduced by CD14.

Endothelial programmed death-1 ligand 1 (PD-L1) regulates CD8+ T-cell mediated injury in the heart

BACKGROUND

PD-L1 and PD-L2 are ligands for the inhibitory receptor programmed death-1 (PD-1), which is an important regulator of immune responses. PD-L1 is induced on cardiac endothelial cells under inflammatory conditions, but little is known about its role in regulating immune injury in the heart.

METHODS AND RESULTS

Cytotoxic T-lymphocyte-mediated myocarditis was induced in mice, and the influence of PD-L1 signaling was studied with PD-L1/L2-deficient mice and blocking antibodies. During cytotoxic T-lymphocyte-induced myocarditis, the upregulation of PD-L1 on cardiac endothelia was dependent on T-cell-derived interferon-gamma, and blocking of interferon-gamma signaling worsened disease. Genetic deletion of both PD-1 ligands [PD-L1/2(-/-)], as well as treatment with PD-L1 blocking antibody, transformed transient myocarditis to lethal disease, in association with widespread polymorphonuclear leukocyte-rich microabscesses but without change in cytotoxic T-lymphocyte recruitment. PD-L1/2(-/-) mice reconstituted with bone marrow from wild-type mice remained susceptible to severe disease, which demonstrates that PD-L1 on non-bone marrow-derived cells confers the protective effect. Finally, depletion of polymorphonuclear leukocytes reversed the enhanced susceptibility to lethal myocarditis attributable to PD-L1 deficiency.

CONCLUSIONS

Myocardial PD-L1, mainly localized on endothelium, is critical for control of immune-mediated cardiac injury and polymorphonuclear leukocyte inflammation.

IFN-gamma prevents early perforin-granzyme-mediated destruction of kidney allografts by inducing donor class I products in the kidney

Interferon-gamma (Ifng) protects organ allografts: mouse kidney allografts lacking Ifng receptors rapidly fail with massive ischemic necrosis around days 5 to 7, reflecting microcirculation failure. We hypothesized that Ifng protects the graft by preventing perforin-granzyme-mediated cytotoxic damage to the microcirculation by inducing class Ia and/or Ib products. We transplanted kidney allografts lacking Ifng receptors into various knockout hosts. The necrosis/congestion phenotype did not require host B cells or IL-4 and IL-13 receptors, but required the T-cell alloresponse: it did not occur if the hosts were syngeneic or T-cell deficient. However, host perforin-granzyme mechanisms were required: no necrosis developed if hosts lacked either perforin or granzymes A and B. The ability of Ifng to protect the allograft required donor class I products: allografts lacking class I products due to Tap1 or beta2 microglobulin deficiency developed a similar necrosis-congestion phenotype at day 7 despite Ifng receptors being present. Thus when host cytotoxic T cells infiltrate organ allografts, Ifng prevents their perforin-granzyme mechanism from compromising the microcirculation by a mechanism requiring donor class Ia or Ib products. We propose that donor class Ia or Ib products are needed to trigger inhibitory receptors on effector T cells.

Inactivation of T-cell receptor-mediated integrin activation prolongs allograft survival in ADAP-deficient mice

BACKGROUND

Signaling through the T cell receptor (TCR) leads to profound changes in the function and properties of T cells, including integrin activation. Adhesion and degranulation promoting adapter protein (ADAP) is an adapter protein linking T cell receptor stimulation to integrin activation. We aim to clarify how disruption of TCR-mediated integrin activation affects alloreactive immune responses.

METHODS

In vitro T cell proliferation and the cytokine production was determined. In vivo cytotoxic T lymphocyte (CTL) activity was measured as well. Allogenic skin and heart transplantation was used to test the in vivo role of ADAP in alloimmune responses. Histology and flow cytometry was applied to analyze the graft infiltrating lymphocytes.

RESULTS

Upon stimulation with allogenic dendritic cells ADAP-deficient T cells displayed impaired proliferative responses compared to wild type (WT) T cells. This was accompanied by significantly decreased production of the cytokine interleukin-2. In contrast, the in vivo CTL activity in ADAP-deficient mice was comparable to that of WT mice. Consistently, we observed a prolongation of fully major histocompatibility complex (MHC)-mismatched heart transplants in ADAP deficient mice. Protection of allogenic heart grafts in ADAP-deficient mice was accompanied by a decrease in the infiltration, proliferation and activation of T cells in the allograft. However, no effect was observed after fully MHC-mismatched skin transplantation.

CONCLUSIONS

We have shown that although ADAP is dispensable for the rejection of allografts, ADAP function plays an important role for the efficacy of graft rejection. ADAP's main function appears to affect the induction phase of the immune response.

Depletion of CD4+ Cells Exacerbates the Cutaneous Response to Acute and Chronic UVB Exposure

Solid organ transplant recipients have a 60-250-fold increased likelihood of developing sunlight-induced squamous cell carcinoma (SCC) compared with the general population. This increased risk is linked to the immunosuppressive drugs taken by these patients to modulate T cell function, thus preventing organ rejection. To determine the importance of T cells in the development of cutaneous SCC, we examined the effects of selectively depleting Skh-1 mice of systemic CD4+ or CD8+ T cells, using monoclonal antibodies, on ultraviolet B (UVB) radiation-induced inflammation and tumor development. Decreases in systemic CD4+ but not CD8+ T cells significantly increased and prolonged the acute UVB-induced cutaneous inflammatory response, as measured by neutrophil influx, myeloperoxidase activity, and prostaglandin E2 levels. Significantly more p53+ keratinocytes were observed in UVB-exposed CD4-depleted than in CD4-replete mice, and this difference was abrogated in mice depleted of neutrophils before UVB exposure. Increased acute inflammation was associated with significantly increased tumor numbers in CD4-depleted mice chronically exposed to UVB. Furthermore, topical treatment with the anti-inflammatory drug celecoxib significantly decreased tumor numbers in both CD4-replete and CD4-depleted mice. Our findings suggest that CD4+ T cells play an important role in modulating both the acute inflammatory and the chronic carcinogenic response of the skin to UVB.