Cytokines and the Th1/Th2 paradigm in transplantation

High-dimensional profiling of immune responses to kidney transplant reveals heterogeneous T helper 1 and B cell effectors associated with rejection

Rejection is a primary cause of allograft dysfunction after kidney transplantation. The diversity of immune subpopulations involved in the different endotypes of rejection remains to be delineated at single-cell resolution. In a cohort of 76 kidney transplant recipients, we conducted high-dimensional immune phenotyping of blood CD4 T and B cells, single-cell RNA and T/B cell receptor sequencing, and plasma cytokine profiling. Phenotypic, transcriptional, and clonal states of CD4T and B cells could significantly distinguish stable allograft states from rejection. Patients undergoing T cell-mediated rejection displayed accumulation of clonally expanded cytotoxic T helper (Th)1 cells and Th17-like cells, associated with predominant naive B cell responses. In contrast, antibody-mediated rejection was characterized by clonal expansion of Th1-polarized T follicular helper cells and effector T-bet+ memory B cells, both of which strongly expressed interleukin 12 and tumor necrosis factor-signaling pathways. Plasma cytokine analysis confirmed mixed Th1/Th17 and Th1/T follicular helper cell-driven inflammatory profiles distinguishing T cell-mediated rejection and antibody-mediated rejection, respectively. CD4T and B cell subpopulations and signatures were validated using bulk RNA-seq analysis of matched kidney allografts and using an independent single-cell RNA-seq data set. These data improve mechanistic understanding of the immune pathogenesis of rejection and support the development of more specific immunosuppressive therapies to treat allograft rejection.

Immunology in corneal transplantation-From homeostasis to graft rejection

Immunology depends on maintaining a delicate balance within the human body, and disruptions can result in conditions such as autoimmune diseases, immunodeficiencies, and hypersensitivity reactions. This balance is especially crucial in transplantation immunology, where one of the primary challenges is preventing graft rejection. Such rejection can lead to organ failure, increased patient mortality, and higher healthcare costs due to the limited availability of donor tissues relative to patient needs. Xenotransplantation, like using porcine corneas for human transplants, offers a potential solution to the donor tissue shortage but faces substantial immunological rejection issues. To prevent rejection in both allo- and xenotransplantation, a deep understanding of how the body maintains immunological balance is essential, particularly since achieving tolerance to non-self tissues is considered the "holy grail" of the field. The cornea, the most frequently transplanted solid organ, has a high acceptance rate due to its immune-privileged status and serves as an ideal model for studying graft rejection mechanisms that disrupt tolerance. However, multiple immune pathways complicate our understanding of these mechanisms. This review examines the rejection mechanisms in corneal transplantation, identifying key cells involved and potential therapeutic strategies to induce and maintain immunological tolerance in both allo- and xenografts across various transplants.

A chimeric anti-vascularization immunomodulator prevents high-risk corneal transplantation rejection via ex vivo gene therapy

Corneal blindness affects more than 5 million individuals, with over 180,000 corneal transplantations (CTs) performed annually. In high-risk CTs, almost all grafts are rejected within 10 years. Here, we investigated adeno-associated virus (AAV) ex vivo gene therapy to establish immune tolerance in the corneal allograft to prevent high-risk CT rejection. Our previous work has demonstrated that HLA-G contributes to ocular immune privilege by inhibiting both immune cells and neovascularization; however, homodimerization is a rate-limiting step for optimal HLA-G function. Therefore, a chimeric protein called single-chain immunomodulator (scIM), was engineered to mimic the native activity of the secreted HLA-G dimer complex and eliminate the need for homodimerization. In a murine corneal burn model, AAV8-scIM significantly reduced corneal vascularization and fibrosis. Next, ex vivo AAV8-scIM gene delivery to corneal allografts was evaluated in a high-risk CT rejection rabbit model. All scIM-treated corneas were well tolerated and transparent after 42 days, while 83% of vehicle-treated corneas were rejected. Histologically, AAV-scIM-treated corneas were devoid of immune cell infiltration and vascularization, with minimal fibrosis at the host-graft interface. The data collectively demonstrate that scIM gene therapy prevents corneal neovascularization, reduces trauma-induced corneal fibrosis, and prevents allogeneic CT rejection in a high-risk large animal model.

The Human Neonatal Skin Fibroblast, an Available Cell Source for Tissue Production and Transplantation, Exhibits Low Risk of Immunogenicity In Vitro

The immunogenicity of allogeneic skin fibroblasts in transplantation has been controversial. Whether this controversy comes from a natural heterogeneity among fibroblast subsets or species-specific differences between human and mouse remains to be addressed. In this study, we sought to investigate whether fibroblasts derived from either adult or neonatal human skin tissues could induce different immune responses toward phagocytosis and T cell activation using in vitro co-culture models. Our results indicate that both phagocytosis and T cell proliferation are reduced in the presence of neonatal skin fibroblasts compared to adult skin fibroblasts. We also show that neonatal skin fibroblasts secrete paracrine factors that are responsible for reduced T cell proliferation. In addition, we show that neonatal skin fibroblasts express less class II human leukocyte antigen (HLA) molecules than adult skin fibroblasts after interferon gamma priming, which might also contribute to reduced T cell proliferation. In conclusion, this study supports the use of allogeneic neonatal skin fibroblasts as a readily available cell source for tissue production and transplantation to treat patients with severe injuries.

Mesenchymal Stromal Cells Suppress T-Cell-Mediated Delayed-Type Hypersensitivity via ALCAM-CD6 Interaction

Mounting evidence suggests mesenchymal stromal cells (MSCs) suppress CD4+ T-cell activation, but whether MSCs directly regulate activation and expansion of allogeneic T cells has not been fully deciphered. Here, we identified that both human and murine MSCs constitutively express ALCAM, a cognate ligand for CD6 receptors on T cells, and investigated its immunomodulatory function using in vivo and in vitro experiments. Our controlled coculture assays demonstrated that ALCAM-CD6 pathway is critical for MSCs to exert its suppressive function on early CD4+CD25- T-cell activation. Moreover, neutralizing ALCAM or CD6 results in the abrogation of MSC-mediated suppression of T-cell expansion. Using a murine model of delayed-type hypersensitivity response to alloantigen, we show that ALCAM-silenced MSCs lose the capacity to suppress the generation of alloreactive IFNγ-secreting T cells. Consequently, MSCs, following ALCAM knockdown, failed to prevent allosensitization and alloreactive T-cell-mediated tissue damage.

B Cell IL-4 Drives Th2 Responses In Vivo, Ameliorates Allograft Rejection, and Promotes Allergic Airway Disease

B cells can be polarized to express various cytokines. The roles of IFNγ and IL-10, expressed respectively by B effector 1 (Be1) and Bregs, have been established in pathogen clearance, tumor growth, autoimmunity and allograft rejection. However, the in vivo role of B cell IL-4, produced by Be2 cells, remains to be established. We developed B-IL-4/13 iKO mice carrying a tamoxifen-inducible B cell-specific deletion of IL-4 and IL-13. After alloimmunization, B-IL-4/13 iKO mice exhibited decreased IL-4⁺ Th2 cells and IL-10⁺ Bregs without impact on Th1, Tregs, or CD8 T cell responses. B-IL-4/13 iKO mice rejected islet allografts more rapidly, even when treated with tolerogenic anti-TIM-1 mAb. In ovalbumin-induced allergic airway disease (AAD), B-IL-4/13 iKO mice had reduced inflammatory cells in BAL, and preserved lung histology with markedly decreased infiltration by IL-4⁺ and IL-5⁺ CD4⁺ T cells. Hence, B cell IL-4 is a major driver of Th2 responses in vivo which promotes allograft survival, and conversely, worsens AAD.

Rocaglamide Prolonged Allograft Survival by Inhibiting Differentiation of Th1/Th17 Cells in Cardiac Transplantation

BACKGROUND

Aglaia (Meliaceae) species are used for treating autoimmune disorders and allergic diseases in Asian countries. Rocaglamide, an extract obtained from Aglaia species, exhibits suppressive effect by regulating the T cell subset balance and cytokine network in cancer. However, whether it can be used in organ transplantation is unknown. In this study, we investigated the antirejection effect and mechanism of action of rocaglamide in a mouse cardiac allograft model.

METHODS

Survival studies were performed by administering mice with phosphate-buffered saline (PBS) (n = 6) and rocaglamide (n = 8). Heart grafts were monitored until they stopped beating. After grafting, the mice were sacrificed on day 7 for histological, mixed lymphocyte reaction (MLR), enzyme-linked immunosorbent assay (ELISA), and flow cytometric analyses.

RESULTS

Rocaglamide administration significantly prolonged the median survival of the grafts from 7 to 25 days compared with PBS treatment (P < 0.001). On posttransplantation day 7, the rocaglamide-treated group showed a significant decrease in the percentage of Th1 cells (7.9 ± 0.9% vs. 1.58 ± 0.5%, P < 0.001) in the lymph nodes and spleen (8.0 ± 2.5% vs. 2.4 ± 1.3%, P < 0.05). Rocaglamide treatment also significantly inhibited the production of Th17 cells (6.4 ± 1.0% vs. 1.8 ± 0.4%, P < 0.01) in the lymph nodes and spleen (5.9 ± 0.3% vs. 2.9 ± 0.8%, P < 0.01). Furthermore, the prolonged survival of the grafts was associated with a significant decrease in IFN-γ and IL-17 levels. Our results also showed that NF-AT activation was inhibited by rocaglamide, which also induced p38 and Jun N-terminal kinase (JNK) phosphorylation in Jurkat T cells. Furthermore, by using inhibitors that suppressed p38 and JNK phosphorylation, rocaglamide-mediated reduction in NF-AT protein levels was prevented.

CONCLUSION

We identified a new immunoregulatory property of rocaglamide, wherein it was found to regulate oxidative stress response and reduce inflammatory cell infiltration and organ injury, which have been associated with the inhibition of NF-AT activation in T cells.

Evaluation of T cell cytokines and their role in recurrent miscarriage

Recurrent miscarriage (RM) is defined as two or more consecutive pregnancy losses that affect approximately 5% of conceived women worldwide. RM is a multi-factorial reproductive problem and has been associated with parental chromosomal abnormalities, embryonic chromosomal rearrangements, uterine anomalies, autoimmune disorders, endocrine dysfunction, thrombophilia, life style factors, and maternal infections. However, the exact cause is still undecided in remaining 50% of cases. Immunological rejection of the embryo due to exacerbated maternal immune reaction against paternal embryonic antigens has been set forth as one of the significant reason for RM. The accurate means that shield the embryo during normal pregnancy from the attack of maternal immune network and dismissal are inadequately implicit. However, it is suggested that the genetically irreconcilable embryo escapes maternal immune rejection due to communication among many vital cytokines exuded at maternal-embryonic interface both by maternal and embryonic cells. Previous investigations suggested the Th1/Th2 dominance in altered immunity of RM patients, according to which the allogenic embryo flees maternal T cell reaction by inclining the Th0 differentiation toward Th2 pathway resulting into diminished pro-inflammatory Th1 immunity. However, recently pro-inflammatory Th17 cells and immunoregulatory Treg cells have been discovered as essential immune players in RM besides Th1/Th2 components. Cytokines are believed to develop a complicated regulatory network so as to establish a state of homeostasis between the semi-allogenic embryo and the maternal immune system. However, an adverse imbalance among cytokines at maternal-embryonic interface perhaps due to their gene polymorphisms may render immunoregulatory means not enough to re-establish homeostasis and thus may collapse pregnancy.

BTLA suppress acute rejection via regulating TCR downstream signals and cytokines production in kidney transplantation and prolonged allografts survival

Acute rejection is a major risk for renal transplant failure. During this adverse process, activated T cells are considered the main effectors. Recently, B and T lymphocyte attenuator (BTLA), a member of the CD28 family receptor, was reported to be a novel inhibitory regulator of T cell activation in heart and pancreatic allograft rejection. Due to the similarity of acute rejection pathways among different organs, we hypothesized that BTLA might play a role in acute rejection of kidney transplant. In renal transplant patients, we observed that BTLA expression was significantly decreased in peripheral CD3+ T lymphocytes of biopsy-proven acute rejection (BPAR) recipients compared with control patients with stable transplanted kidney functions. Remarkably, overexpression of BTLA in the rat model was found to significantly inhibit the process of acute rejection, regulate the postoperative immune status, and prolong allograft survival. BTLA overexpression significantly suppressed IL-2 and IFN-γ production and increased IL-4 and IL-10 production both in vivo and in vitro. Moreover, vital factors in T-cell signaling pathways, including mitogen-associated protein kinases (MAPK), nuclear factor-kappa B (NF-κB) and nuclear factor of activated T cells (NFAT), were also significantly repressed by BTLA overexpression. Therefore, BTLA can suppress acute rejection and regulate allogeneic responses of kidney transplant by regulating TCR downstream signals and inflammatory cytokines production to improve allografts outcomes.

Inflammatory mediators: a causal link to hypertension during preeclampsia

Preeclampsia (PE) is a hypertensive disorder that occurs after 20 weeks of gestation, implicating the placenta as a key offender. PE is associated with an imbalance among B lymphocytes, CD4+ T lymphocytes, NK cells and increased inflammatory cytokines. During early onset PE, trophoblast invasion and placentation are impaired, leading to reduced blood flow to the fetus. In all spectrums of this disorder, a shift towards a pro-inflammatory state where regulatory cells and cytokines are decreased occurs. Specifically, inflammatory CD4+ T-cells and inflammatory cytokines are increased while CD4+ T regulatory cells (Tregs) and immunosuppressive cytokines such as IL-4 and IL-10 are decreased resulting in B cell activation, production of autoantibodies, endothelial dysfunction and hypertension associated with PE. However, the stimulus for these imbalances is unknown and need to be fully understood so that effective treatments that target the pathogenesis of the disease can be designed. Therefore, this review will focus on the pathways involving CD4+ , TH1, TH2, Tregs, TH17s, B cells, and NK cells in the pathophysiology of PE. LINKED ARTICLES: This article is part of a themed section on Immune Targets in Hypertension. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.12/issuetoc.

Characterization of eomesodermin and T-bet expression by allostimulated CD8+ T cells of healthy volunteers and kidney transplant patients in relation to graft outcome

Memory T cell (Tmem) responses play a critical role in the outcome of allo-transplantation. While the role of the T-box transcription factor Eomesodermin (Eomes) in the maintenance of antigen-specific Tmem is well studied, little is known about Eomes+ CD8+ T cell responses after transplantation. We evaluated the phenotype and function of allo-reactive Eomes+ CD8+ T cells in healthy volunteers and kidney transplant patients and their relation to transplant outcome. High Eomes expression by steady-state CD8+ T cells correlated with effector and memory phenotype. Following allo-stimulation, the expression of both the T-box proteins Eomes and T-bet by proliferating cells increased significantly, where high expression of Eomes and T-bet correlated with higher incidence of allo-stimulated IFNγ+ TNFα+ CD8+ T cells. In patients with no subsequent rejection, Eomes but not T-bet expression by donor-stimulated CD8+ T cells, increased significantly after transplantation. This was characterized by increased Eomeshi T-bet-/lo and decreased Eomes-/lo T-bethi CD8+ T cell subsets, with no significant changes in the Eomeshi T-bethi CD8+ T cell subset. No upregulation of exhaustion markers programmed-death-1 (PD-1) and cytotoxic-T-lymphocyte-associated-antigen-4 (CTLA4) by donor-stimulated Eomes+ CD8+ T cells was observed. Before transplantation, in patients without rejection, there were higher incidences of Eomeshi T-bet-/lo , and lower incidences of Eomeshi T-bethi and Eomes-/lo T-bethi donor-stimulated CD8+ T cell subsets, compared to those with subsequent rejection. Overall, our findings indicate that high Eomes expression by allo-stimulated T-bet+ CD8+ T cells is associated with enhanced effector function, and that an elevated incidence of donor-stimulated CD8+ T cells co-expressing high levels of Eomes and T-bet before transplantation, may correlate with an increased incidence of acute cellular rejection.

Elevated percentage of CD3+T cells and pregnancy outcome in women with recurrent pregnancy loss

BACKGROUND

Even though the immune factor is not yet established as a cause of recurrent pregnancy loss (RPL), tons of other studies have shown that a significant proportion of immune abnormalities exist in RPL.

METHODS

We conducted a retrospective cohort study with 850 women who were diagnosed with RPL. The percentages of CD3⁺, CD3⁺CD4⁺ and CD3⁺CD8⁺T cells of each participant, detected by flow cytometry, were obtained before pregnancy and at 6 weeks of gestation as part of their routine medical examination.

RESULTS

Peripheral blood CD3⁺ T cells prior to pregnancy (at baseline), increased significantly in women who had a miscarriage compared with the subsequent live birth group. Moreover, the percentage of CD3⁺ and CD3⁺CD4⁺T cells during pregnancy increased significantly as compared with the baseline level. After adjusting for potential confounders, the multiple regression equation showed that the CD3⁺ T cells <67.84% was associated with the risk of miscarriage (OR 1.05, 95% CI, 1.01 to 1.11, p = .04). Additionally, a nonlinear relationship was observed between the percentage of CD3⁺T cells and the risk of miscarriage.

CONCLUSIONS

The risk of miscarriage increased as the percentage of population with CD3+ value below 67.84% has increased, nevertheless, the miscarriage risk did not increase further when the level of CD3⁺T cells was >67.84%.

Role of programmed death ligand 1 and Kupffer cell in immune regulation after orthotopic liver transplantation in rats

INTRODUCTION

Role of programmed death ligand 1 (PD-L1) and Kupffer cells (KCs) in liver transplantation immune regulation was unclear.

METHODS

Lewis and Brown-Norway (BN) rats were assigned to LEW-BN group (Lewis-to-BN liver transplantation) and BN-BN group (BN-to-BN). Receipts were sacrificed for histology and assessment of cytokines and PD-L1 production. Effect of PD-L1 and KCs on T cells (TCs) was monitored by co-culture of ³H-Thymidine TCs. KCs transfected with PD-L1-shRNA interference plasmids were co-cultured with TCs, PD-L1 expression and cytokines production were measured respectively.

RESULTS

Recipients in BN-BN group survived a long time while acute rejection was found in LEW-BN group. ELISA showed plasma levels of IL-2, IFN-γ and TNF-α in BN-BN group were significantly lower and levels of IL-10 were significantly higher than that in LEW-BN group on day 7 after transplantation (P<0.05). PD-L1 expression of KCs in BN-BN group was significantly higher than that in the LEW-BN group (P<0.05). Proliferation rate of TCs in KCs+TCs group was significantly lower and its apoptosis rate was significantly higher than that in TCs group (P<0.05). IL-2, TNF-α and INF-γ levels were remarkably higher and IL-10 levels were lower in KCs+TCs group than that in TCs group (P<0.05). Levels of IL-2, IFN-γ and TNF-α in transfection group were significantly higher and that of IL-10 was notably lower than that in the un-transfected group (P<0.05).

CONCLUSION

KCs with high expression of PD-L1 could significantly suppress the proliferation and function of TCs. Silencing the expression of PD-L1 in KCs in vivo could restore the function of TCs.

Sleep influences the immune response and the rejection process alters sleep pattern: Evidence from a skin allograft model in mice

INTRODUCTION

Sleep generally regulates immune functions in a supportive manner and can affect parameters that are directly involved in the rejection process.

STUDY OBJECTIVES

The first objective was to assess whether sleep deprivation (SD) or sleep restriction (SR) affects the allograft rejection process in mice. The second objective was to investigate whether the rejection process itself modulates the sleep pattern of allografted mice.

DESIGN

Adult BALB/c and C57BL/6J male mice were used as the donors and recipients, respectively, except for the syngeneic group (ISOTX), which received skin from mice of the same strain (C57BL/6J). The recipients were randomly assigned to either one of two control groups - TX (allogenic) or ISOTX (syngeneic) - which underwent stereotaxic surgery to enable sleep recording prior to the allograft but were not sleep deprived; one of two paradoxical sleep deprived groups - SDTX and TXSD - which underwent 72h of continuous SD either before or after the allograft respectively, and one of two sleep restricted groups - SRTX and TXSR - which underwent 21h of SD and 3h of sleep for 15days either before or after the allograft respectively.

INTERVENTIONS

The skin allograft was inspected daily to determine the survival time, expected as 8.0±0.4days in this transplant model under no treatment. The sleep pattern was controlled throughout the rejection process in the SD and SR groups. Draining lymph nodes, spleen, blood and skin grafts were harvested on the 5th day after transplantation for evaluation of the immune parameters related to allograft rejection.

MEASUREMENTS AND RESULTS

In the control groups, we observed a reduction in paradoxical sleep throughout the entire allograft rejection process. Acute and chronic experimental sleep loss in the SD and SR groups produced marked alterations in the immune response. Both SD and SR prolonged allograft survival compared to the non-sleep-deprived group. There were reductions in the following parameters involved in the allograft rejection under sleep loss: CD4⁺ and CD8⁺ T cell subpopulations in the peripheral lymph organs and spleen, circulating sIL-2R levels, graft-infiltrating CD4⁺ T cells and skin allograft global gene expression.

CONCLUSIONS

We provide, as far as we are aware, the first evidence in vivo that the immune response can alter the normal sleep pattern, and that sleep loss can conversely affect the immune response related to graft rejection.

Role of inflammatory mediators in patients with recurrent pregnancy loss

OBJECTIVE

To examine interleukin-12 (IL-12), IL-18, IFN-γ, intracellular adhesion molecule-1 (ICAM-1), leukemia inhibitory factor (LIF), and migration inhibitory factor (MIF) levels in precisely-timed blood and endometrial tissue samples from women with idiopathic recurrent pregnancy loss (RPL).

DESIGN

Case-control study.

SETTING

University hospital.

PATIENT(S)

Twenty-one women with RPL and 20 women with proven fertility (controls).

INTERVENTION(S)

Primary endometrial cells and blood samples during the midsecretory phase (days 19-23).

MAIN OUTCOME MEASURE(S)

Detection of IL-12, IL-18, IFN-γ, ICAM-1, LIF, and MIF via enzyme-linked immunosorbent assay in both blood and endometrial tissue samples.

RESULT(S)

The blood and tissue levels of IL-12, IL-18, and IFN-γ were statistically significantly higher, and the blood and tissue levels of LIF and MIF were statistically significantly lower in patients with RPL. Only the level of tissue ICAM-1 was higher in patients with RPL. There was a strong correlation between blood and tissue level measurements of IL-12, IL-18, LIF, and MIF.

CONCLUSION(S)

Our findings support the hypothesis that inflammatory processes may contribute to pregnancy loss, possibly through their role in implantation. We found that blood and tissue levels of IL-18, LIF, and MIF, and tissue levels of IL-12, IFN-γ, and ICAM-1 have statistically significant prognostic relevance.

Eosinophil count, allergies, and rejection in pediatric heart transplant recipients

BACKGROUND

Allograft rejection and long-term immunosuppression remain significant challenges in pediatric heart transplantation. Pediatric recipients are known to have fewer rejection episodes and to develop more allergic conditions than adults. A T-helper 2 cell dominant phenotype, manifested clinically by allergies and an elevated eosinophil count, may be associated with immunologic quiescence in transplant recipients. This study assessed whether the longitudinal eosinophil count and an allergic phenotype were associated with freedom from rejection.

METHODS

This single-center, longitudinal, observational study included 86 heart transplant patients monitored from 1994 to 2011. Post-transplant biannual complete blood counts, allergic conditions, and clinical characteristics related to rejection risk were examined.

RESULTS

At least 1 episode of acute cellular rejection (ACR) occurred in 38 patients (44%), antibody-mediated rejection (AMR) occurred in 11 (13%), and 49 patients (57%) were diagnosed with an allergic condition. Patients with ACR or AMR had a lower eosinophil count compared with non-rejectors (p = 0.011 and p = 0.022, respectively). In the multivariable regression analysis, the presence of panel reactive antibodies to human leukocyte antigen I (p = 0.014) and the median eosinophil count (p = 0.011) were the only independent covariates associated with AMR. Eosinophil count (p = 0.010) and female sex (p = 0.009) were independent risk factors for ACR. Allergic conditions or young age at transplant were not protective from rejection.

CONCLUSIONS

This study demonstrates a novel association between a high eosinophil count and freedom from rejection. Identifying a biomarker for low rejection risk may allow a reduction in immunosuppression. Further investigation into the role of the T-helper 2 cell phenotype and eosinophils in rejection quiescence is warranted.

Potentially pathogenic immune cells and networks in apparently healthy lacrimal glands

Lacrimal glands of people over 40 years old frequently contain lymphocytic infiltrates. Relationships between histopathological presentation and physiological dysfunction are not straightforward. Data from rabbit studies have suggested that at least two immune cell networks form in healthy lacrimal glands, one responding to environmental dryness, the other to high temperatures. New findings indicate that mRNAs for several chemokines and cytokines are expressed primarily in epithelial cells; certain others are expressed in both epithelial cells and immune cells. Transcript abundances vary substantially across glands from animals that have experienced the same conditions, allowing for correlation analyses, which detect clusters that map to various cell types and to networks of coordinately functioning cells. A core network--expressing mRNAs including IL-1α, IL-6, IL-17A, and IL-10--expands adaptively with exposure to dryness, suppressing IFN-γ, but potentially causing physiological dysfunction. High temperature elicits concurrent increases of mRNAs for prolactin (PRL), CCL21, and IL-18. PRL is associated with crosstalk to IFN-γ, BAFF, and IL-4. The core network reacts to the resulting PRL-BAFF-IL-4 network, creating a profile reminiscent of Sjögren's disease. In a warmer, moderately dry setting, PRL-associated increases of IFN-γ are associated with suppression of IL-10 and augmentations of IL-1α and IL-17, creating a profile reminiscent of severe chronic inflammation.

Immunology of Corneal Allografts: Insights from Animal Models

Corneal transplantation stands alone as the most common and successful form of solid organ transplantation. Even though HLA matching and systemic antirejection drugs are not routinely used, 90% of the first time corneal allografts will succeed. By contrast, all other major categories of organ transplantation require HLA matching and the use of systemically administered immunosuppressive drugs. This remarkable success of corneal transplants under these conditions is an example of "immune privilege" and is the primary reason for the extraordinary success of corneal transplantation. A number of dogmas have emerged over the past century to explain immune privilege and the immunobiology of corneal transplantation. Many of these dogmas have been based largely on inferences from clinical observations on keratoplasty patients. The past 30 years have witnessed a wealth of rodent studies on corneal transplantation that have tested hypotheses and dogmas that originated from clinical observations on penetrating keratoplasty patients. Rodent models allow the application of highly sophisticated genetic and immunological tools for testing these hypotheses in a controlled environment and with experiments designed prospectively. These studies have validated some of the widely held assumptions based on clinical observations and in other cases, previous dogmas have been replaced with new insights that could only come from prospective studies performed under highly controlled conditions. This review highlights some of the key dogmas and these widely held assumptions that have been scrutinized through the use of rodent models of penetrating keratoplasty. This review also makes note of new immunological principles of corneal immunology that have emerged from rodent studies on corneal transplantation that most likely would not have been revealed in studies on corneal transplantation patients.

Regulation of the Anti-Inflammatory Cytokines Interleukin-4 and Interleukin-10 during Pregnancy

Inflammation mediated by both innate and adaptive immune cells is necessary for several important processes during pregnancy. Pro-inflammatory immune cell activation plays a critical role in embryo implantation, placentation, and parturition; however dysregulation of these cells can lead to detrimental pregnancy outcomes including spontaneous abortion, fetal growth restriction, maternal pathology including hypertensive disorders, or fetal and maternal death. The resolution of inflammation plays an important role throughout pregnancy and is largely mediated by immune cells that produce interleukin (IL)-4 and IL-10. The temporal and spatial aspects of reducing inflammation during pregnancy represent a complex process that if not functioning optimally can lead to persistent inflammation and pregnancy complications. In this review, we examine how immune cells that produce IL-4 and IL-10 are regulated throughout pregnancy as well as the effects that reduced IL-4 and IL-10 signaling has on fetal and maternal physiology.

CD154 blockade modulates the ratio of Treg to Th1 cells and prolongs the survival of allogeneic corneal grafts in mice

Administration of anti-CD154 monoclonal antibody (mAb) may prolong the survival of an allograft; however, the associated therapeutic mechanisms remain poorly understood. This study aimed to evaluate the effects of anti-CD154 mAb on T-cell responses in a mouse model of corneal allograft transplantation. BALB/c mice were transplanted with corneal grafts from C57BL/6 mice and treated intraperitoneally with 250 μg anti-CD154 mAb or isotype IgG on days 0, 3 and 6 post surgery. The transparency of the corneal grafts was evaluated for potential rejection signs by slit-lamp biomicroscopy and histopathology. The percentages of CD4⁺ T, Tim-3⁺CD4⁺ T helper (Th) 1 and CD4⁺CD25⁺Foxp3⁺ regulatory T cells (Tregs) in the spleen, ipsilateral draining lymph nodes and corneal grafts, and the frequency of splenic IFN-γ⁺ and IL-10⁺ expression in CD4⁺ T cells were determined by flow cytometry. Moreover, the ratio of Tregs to Th1 cells was calculated and the suppressive activity of splenic Tregs was measured. Anti-CD154 neutralization significantly prolonged the survival of the corneal allograft (P=0.0012) and reduced the numbers of inflammatory infiltrates in the corneal graft. In the spleen and lymph nodes, anti-CD154 treatment reduced the frequency of CD4⁺ T cells, Tregs and particularly Th1 cells. In the corneal allografts, anti-CD154 treatment downregulated graft-infiltrated CD4⁺ T cells and Th1 cells, but increased graft-infiltrated Tregs. Furthermore, anti-CD154 treatment increased the frequency of splenic IL-10⁺CD4⁺ T cells and decreased the concentration of splenic IFN-γ⁺CD4⁺ T cells. As a result, the ratio of Tregs to Th1 cells in the anti-CD154-treated recipients increased. Anti-CD154 treatment did not enhance the suppressive activity of Tregs in the recipients. The results indicate that the therapeutic effects of anti-CD154 mAb on prolonging the survival of the corneal allograft may be associated with an increased ratio of Tregs to Th1 cells in mice.

Profile of maternal CD4 T-cell effector function during normal pregnancy and in women with a history of recurrent miscarriage

The traditional paradigm suggests that during normal pregnancy maternal immunological tolerance of the allogenic fetus is association with a maternal T-lymphocyte shift from a Th1 to a Th2 phenotype, with the opposite effect reported in patients with recurrent miscarriage. However, studies on maternal peripheral blood are conflicting. In the present study, we characterized the maternal CD4 T-cell effector subsets, including the recently described Th17 subset, during normal pregnancy (cross-sectional cohort, n=71; longitudinal cohort, n=17) and contrasted this with women with recurrent miscarriage (n=24). Longitudinal analysis of peripheral blood from normal pregnancy demonstrated a fall in the percentage of Th17 cells between the first and second trimester (P≤0.05), but no significant changes were observed across gestation or the post-natal period in Th1 or Th2 subsets. In contrast, in women with a history of recurrent miscarriage, an elevated proportion of Th17 (0.314% compared with 0.097%; P=0.0009) and Th1 (12.4% compared with 5.3%; P=0.0002) cells was detected. The suggestion that Th17 cells may have a role in the normal events of implantation and early pregnancy requires further evaluation and mechanistic studies. The results of the present study, by conducting a careful longitudinal analysis, demonstrate that a peripheral Th1/Th2 shift is not a requirement for normal pregnancy. By contrast, the profound increase in Th1 and Th17 cells in women with recurrent miscarriage indicates that peripheral immunological dysfunction may be important in this group specifically, and these assays may be important in guiding therapeutic interventions in this group and warrant further investigation to determine whether they are predictive of outcome or responses to immunomodulatory therapy.

Trogocytosis in allogeneic transplants: donor cells take on the recipients identity

Trogocytosis has been identified as a mechanism of cell communication between immune cells. Unlike the more common receptor-ligand signaling, trogocytosis results in the transfer of intact and functional surface proteins between cells. For example, antigen presenting cells in contact with T cells exchange proteins which results in the T-cell acquiring antigen presentation capabilities. This allows for the newly activated T cells to stimulate other T cells thus amplifying the immune response. We have recently demonstrated that during allogeneic hematopoietic stem cell transplantation the donor cells obtain recipient MHC class I proteins by trogocytosis. The effect is a donor cell that can masquerade as a recipient cells and evade detection by NK cells and macrophages.

Corneal transplantation and immune privilege

Corneal transplants have been successfully performed in human subjects for over 100 years and enjoy an immune privilege that is unrivaled in the field of transplantation. Immune privilege is defined as the reduced incidence and tempo in the immune rejection of corneal allografts compared to other categories of organ allografts performed under the same conditions. Skin allografts transplanted across various MHC or minor histocompatibility barriers undergo rejection in approximately 100% of the hosts. By contrast, orthotopic corneal allografts experience long-term survival in 50% to >90% of the hosts, depending on the histocompatibility barriers that confront the host. The capacity of corneal allografts to evade immune rejection is attributable to multiple anatomical, physiological and immunoregulatory conditions that conspire to prevent the induction and expression of alloimmunity.

Implications for Interleukin-33 in solid organ transplantation

Interleukin(IL)-33 is a member of the IL-1 cytokine family that has been attributed T helper (Th) type 2 immunity-promoting capacity. However, new studies indicate that IL-33 is a multifunctional protein that acts as transcriptional/signaling repressor, functions as an alarmin alerting the immune system to necrosis, as well as serves as a cytokine that targets cells expressing ST2, the IL-33 receptor. Interestingly, IL-33 is also emerging as a pleiotropic cytokine. Depending on the innate or adaptive immune cells targeted by IL-33, it can not only promote type 2, but also IFN-γ dominated type 1 immunity. In addition, IL-33 expands regulatory T cells. In this review, we assimilate the current knowledge of IL-33 immunobiology and discuss how IL-33 may mediate such diverse roles in the immune response to pathogens and development of immune-mediated pathologies. The function of IL-33 in shaping alloimmune responses to transplanted organs is poorly explored, but a particularly beneficial role of IL-33 in experimental heart transplant models is summarized. Finally, given the implication of IL-33 in pathologies of the lung and intestine, we discuss how IL-33 may contribute to the comparatively poor outcomes following transplantation of these two organs.

Galectin-1 prolongs survival of mouse liver allografts from Flt3L-pretreated donors

Liver allografts are spontaneously accepted across MHC barriers in mice. The mechanisms underlying this phenomenon remain poorly understood. Galectin-1, an endogenous lectin expressed in lymphoid organs, plays a vital role in maintaining central and peripheral tolerance. This study was to investigate the role of galectin-1 in spontaneous tolerance of liver allografts in mice, and to evaluate the therapeutic effects of galectin-1 on liver allograft rejection induced by donor Flt3L pretreatment. Blockade of the galectin-1 pathway via neutralizing antigalectin-1 mAb did not affect survival of the liver allografts from B6 donors into C3H recipients. Administration of rGal-1 significantly prolonged survival of liver allografts from Flt3L-pretreated donors and ameliorated Flt3L-triggered liver allograft rejection. This effect was associated with increased apoptosis of T cells in both allografts and spleens, decreased frequencies of Th1 and Th17 cells, decreased expression of Th1-associated cytokines (IL-12, IL-2 and IFN-γ), Th17-associated cytokines (IL-23 and IL-17) and granzyme B, in parallel with selectively increased IL-10 expression in liver allografts. In vitro, galectin-1 inhibited Flt3L-differentiated DC-mediated proliferation of allo-CD4(+) T cells and production of IFN-γ and IL-17. These data provide new evidence of the potential regulatory effects of galectin-1 in alloimmune responses in a murine model of liver transplantation.

Intact B7-H3 signaling promotes allograft prolongation through preferential suppression of Th1 effector responses

Ligands of the B7 family provide both positive and negative costimulatory signals to the CD28 family of receptors on T lymphocytes, the balance of which determines the immune response. B7-H3 is a member of the B7 family whose function in T-cell activation has been the subject of some controversy: in autoimmunity and tumor immunity, it has been described as both costimulatory and coinhibitory, while in transplantation, B7-H3 signaling is thought to contribute to graft rejection. However, we now demonstrate results to the contrary. Signaling through a putative B7-H3 receptor prolonged allograft survival in a fully MHC-mismatched cardiac model and promoted a shift toward a Th2 milieu; conversely, B7-H3 blockade, achieved by use of a blocking antibody, resulted in accelerated rejection, an effect associated with enhanced IFN-γ production. Finally, graft prolongation achieved by CTLA4 Ig was shortened both by B7-H3 blockade and the absence of recipient B7-H3. These findings suggest a coinhibitory role for B7-H3. However, experience with other CD28/B7 family members suggests that immune redundancy plays a crucial role in determining the functions of various pathways. Given the abundance of conflicting data, it is plausible that, under differing conditions, B7-H3 may have both positive and negative costimulatory functions.

IL-6 promotes cardiac graft rejection mediated by CD4+ cells

IL-6 mediates numerous immunologic effects relevant to transplant rejection; however, its specific contributions to these processes are not fully understood. To this end, we neutralized IL-6 in settings of acute cardiac allograft rejection associated with either CD8(+) or CD4(+) cell-dominant responses. In a setting of CD8(+) cell-dominant graft rejection, IL-6 neutralization delayed the onset of acute rejection while decreasing graft infiltrate and inverting anti-graft Th1/Th2 priming dominance in recipients. IL-6 neutralization markedly prolonged graft survival in the setting of CD4(+) cell-mediated acute rejection and was associated with decreased graft infiltrate, altered Th1 responses, and reduced serum alloantibody. Furthermore, in CD4(+) cell-dominated rejection, IL-6 neutralization was effective when anti-IL-6 administration was delayed by as many as 6 d posttransplant. Finally, IL-6-deficient graft recipients were protected from CD4(+) cell-dominant responses, suggesting that IL-6 production by graft recipients, rather than grafts, is necessary for this type of rejection. Collectively, these observations define IL-6 as a critical promoter of graft infiltration and a shaper of T cell lineage development in cardiac graft rejection. In light of these findings, the utility of therapeutics targeting IL-6 should be considered for preventing cardiac allograft rejection.

B7-H4 Pathway in Islet Transplantation and β-Cell Replacement Therapies

Type 1 diabetes (T1D) is a chronic autoimmune disease and characterized by absolute insulin deficiency. β-cell replacement by islet cell transplantation has been established as a feasible treatment option for T1D. The two main obstacles after islet transplantation are alloreactive T-cell-mediated graft rejection and recurrence of autoimmune diabetes mellitus in recipients. T cells play a central role in determining the outcome of both autoimmune responses and allograft survival. B7-H4, a newly identified B7 homolog, plays a key role in maintaining T-cell homeostasis by reducing T-cell proliferation and cytokine production. The relationship between B7-H4 and allograft survival/autoimmunity has been investigated recently in both islet transplantation and the nonobese diabetic (NOD) mouse models. B7-H4 protects allograft survival and generates donor-specific tolerance. It also prevents the development of autoimmune diabetes. More importantly, B7-H4 plays an indispensable role in alloimmunity in the absence of the classic CD28/CTLA-4 : B7 pathway, suggesting a synergistic/additive effect with other agents such as CTLA-4 on inhibition of unwanted immune responses.

Cytokines in recurrent pregnancy loss

BACKGROUND

Recurrent pregnancy loss (RPL) is defined as the occurrence of three or more consecutive miscarriages prior to 20 weeks gestation. Exaggerated maternal immune response to fetal antigens has been proposed to be one of the mechanisms underlying recurrent pregnancy loss.

METHOD

A comprehensive literature search was conducted from the websites of the National Library of Medicine (http://www.ncbl.nlm.nih.gov) and Pubmed Central, the US National Library of Medicine's digital archive of life sciences literature (http://www.pubmedcentral.nih.gov/). The data was assessed from books and journals that published relevant articles in this field.

RESULT

In normal pregnancy, tolerance of the genetically incompatible fetus by the maternal immune system depends on the interactions of an array of cytokines secreted by maternal and fetal cells at the site of implantation. Earlier research indicated that altered immunity in RPL is dominated by the Th1/Th2 hypothesis, which proposed that the fetus escapes maternal-derived T-cell responses through skewing the Th0 differentiation toward Th2 pathway which dampens pro-inflammatory Th1-type immunity. Recent studies indicate the role of proinflammatory Th17 cells and immunoregulatory Treg cells in RPL in addition to Th1/Th2 interactions.

CONCLUSION

Cytokines form a complex regulatory network which maintains homeostasis between the fetal unit and the maternal immune system. If this delicate balance is adversely affected, immunoregulatory mechanisms may be insufficient to restore homeostasis and this may lead to pregnancy failure.

Immunosuppression involving soluble CD83 induces tolerogenic dendritic cells that prevent cardiac allograft rejection

BACKGROUND

Dendritic cells (DCs) are crucial regulators of immunity and important in inducing and maintaining tolerance. Here, we investigated the potential of a novel DC-immunomodulating agent, soluble CD83 (sCD83), in inducing transplant tolerance.

METHODS

We used the C3H-to-C57BL/6 mouse cardiac transplantation model that exhibits a combination of severe cell-mediated rejection and moderate antibody-mediated rejection and investigated whether sCD83 could augment a combination therapy consisting of Rapamycin (Rapa) and anti-CD45RB monoclonal antibody (α-CD45) to prolong allograft survival.

RESULTS

Monotherapies consisting of Rapa and α-CD45 were incapable of preventing rejection. However, all treatments involving sCD83 were capable of (1) down-modulating expression of various DC surface molecules, such as major histocompatibility complex class II and costimulatory molecules, (2) reducing the allogeneic stimulatory capacity of the DCs, and (3) significantly inhibiting antidonor antibody responses. Most striking results were observed in the triple therapy-treated group, sCD83Rapaα-CD45, where cell-mediated rejection and antibody-mediated rejection were abrogated for over 100 days. Donor-specific tolerance was achieved in long-term surviving recipients, because donor skin transplants were readily accepted for an additional 100 days, whereas third-party skin grafts were rejected. Success of triple therapy treatment was accompanied by enhancement of tolerogenic-DCs that conferred antigen-specific protection on adoptive transfer to recipients of an allogeneic heart graft.

CONCLUSIONS

Our study revealed that sCD83 is capable of attenuating DC maturation and function, and inducing donor-specific allograft tolerance, in the absence of toxicity. Thus, sCD83 seems to be a safe and valuable counterpart to current DC-modulating agents.

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.

IL-17 promotes immune privilege of corneal allografts

Corneal allograft rejection has been described as a Th1-mediated process involving IFN-γ production. However, it has been reported that corneal allograft rejection soars in IFN-γ(-/-) mice or mice treated with anti-IFN-γ mAb. Th17 is a recently described IL-17A-producing Th cell population that has been linked to renal and cardiac graft rejection, which was originally thought to be Th1-mediated. We tested the hypothesis that Th17 cells mediate corneal allograft rejection in an IL-17A-dependent fashion and unexpectedly found that depletion of IL-17A increased the incidence of rejection to 90%. We demonstrate that the exacerbated rejection following depletion of IL-17A did not result from a loss of cross-regulation of Th1 cells or exaggerated delayed-type hypersensitivity responses. Instead, inhibition of the Th1 or Th17 cell lineages promoted the emergence of a Th2 cell subset that independently mediated allograft rejection. These findings demonstrate that IL-17A is not required for corneal allograft rejection and may instead contribute to the immune privilege of corneal allografts.

Effect of emodin in suppressing acute rejection following liver allograft transplantation in rats

OBJECTIVE

To investigate the mechanism of action of emodin for suppressing acute allograft rejection in a rat model of liver transplantation.

METHODS

Brown Norway (BW) recipient rats of orthotopic liver transplantation (OLT) were divided into three groups, Group A receiving isografting (with BW rats as donor), Group B receiving allografting (with Lewis rats as donor), Group C receiving allografting and emodin treatment (50 mg/kg daily). They were sacrificed on day 7 of post-transplantation, and their hepatic histology, plasma cytokine levels, and T-cell subset expression were detected.

RESULTS

Compared with those in Group A, rats: in Group B exhibited severe allograft rejection with a rejection activity index (RAI) of 7.67+/-0.98, extensive hepatocellular apoptosis with an apoptosis index (AI) of 35.83+/-2.32, and elevated plasma levels of interleukin-2 (IL-2), interleukin-10 (IL-10), tumor necrosis factor-alpha (TNF-alpha), CD4(+) and CD4 CD4(+)/CD8(+) ratio. However, recipients in Group C showed a decrease in histological grade of rejection and hepatocellular apoptosis, as well as a decrease in plasma levels of IL-2, TNF-alpha, CD4(+) and CD4(+)/CD8(+) ratio, but elevated levels of IL-10 as compared with the allograft group.

CONCLUSION

Post-OLT acute rejection could be attenuated by emodin, its mechanism of action may be associated with protecting hepatocytes from apoptosis, polarizing the Th 1 paradigm to Th2, and inhibiting the proliferation of CD4(+) T cell in plasma.

Immune reconstitution inflammatory syndrome in non-HIV immunocompromised patients

PURPOSE OF REVIEW

In the era of highly active antiretroviral therapy, immune reconstitution inflammatory syndrome has become well recognized in the HIV-infected population. However, little is known about its occurrence in non-HIV immunocompromised hosts. The present review aims to propose the pathogenesis of immune reconstitution inflammatory syndrome, summarize its occurrence in immunocompromised patients without HIV infection, and suggest potential treatment options.

RECENT FINDINGS

Immune reconstitution inflammatory syndrome is exuberant and dysregulated inflammatory responses to invading microorganisms. It manifests when an abrupt shift of host immunity from an anti-inflammatory and immunosuppressive status towards a pathogenic proinflammatory state occurs as a result of rapid decreases or removal of factors promoting immunosuppression or inhibiting inflammation. In addition to HIV-infected patients, immune reconstitution inflammatory syndrome has also been observed in solid organ transplant recipients, women during the postpartum period, neutropenic patients, and tumor necrosis factor antagonist recipients. Corticosteroids are the most commonly employed treatment, whereas other potential agents based on its pathogenesis deserve further investigation.

SUMMARY

Non-HIV immunocompromised hosts develop immune reconstitution inflammatory syndrome when the sudden change in the dominant T helper responses to inflammation is not well balanced by anti-inflammatory responses. Judicious manipulation of host immunity and timely recognition of immune reconstitution inflammatory syndrome as we deal with the infections in these populations is critical to limit or avoid the harm by immune reconstitution inflammatory syndrome.

Histological differences in full-thickness vs. lamellar corneal pig-to-rabbit xenotransplantation

To evaluate the differences in graft survival and histopathological characteristics between full-thickness and lamellar orthotopic corneal xenotransplantation in a pig-to-rabbit model, we orthotopically transplanted a full-thickness or the anterior half of a pig's cornea onto the OD of 16 rabbits. As a result, the median survival were 16.83 and 29.07 days for the full-thickness and lamellar xenografts, respectively (P = 0.0005). Histologically, the full-thickness corneal xenografts had massive infiltration by eosinophils, whereas the lamellar xenografts showed predominantly mononuclear infiltrates (P < 0.05). Given these preliminary findings, lamellar corneal xenografts in rabbits survived longer than the full-thickness xenografts and each type of graft demonstrated different rejection mechanisms.

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.

Relative roles of Th1 and Th17 effector cells in allograft rejection

PURPOSE OF REVIEW

Despite advances in immunosuppression, allograft rejection remains a significant challenge to the long-term success of solid-organ transplantation. Whilst allorecognition pathways are clearly central to rejection, the effector mechanisms of this process are less defined. T helper (Th) type 17 cells are a recently described CD4 T-cell subset, and have been implicated in a range of autoimmune and inflammatory conditions that were previously thought to be Th1 mediated. In light of these developments, this review examines the relative roles of these subsets in allograft rejection.

RECENT FINDINGS

Th1 cells are characterized by production of the cytokine interferon-gamma, which has recently been described as having both pro- and anti-inflammatory effects, including a role in regulatory T-cell function. A number of clinical studies show that serum and intragraft interferon-gamma levels positively correlate with episodes of acute rejection, although increased interleukin-17 expression has also been reported in transplants undergoing rejection. Interestingly, a complex interplay between Treg and Th17 development has recently been demonstrated, with transforming growth factor-beta being necessary for both.

SUMMARY

Current data indicate the presence of both subsets during allograft rejection, although their precise role is unclear. An improved understanding of the factors that influence the differentiation and function of these cell types will assist in the development of future immunomodulatory therapies.

C5 blockade with conventional immunosuppression induces long-term graft survival in presensitized recipients

We explored whether a functionally blocking anti-C5 monoclonal antibody (mAb) combined with T- and B-cell immunosuppression can successfully prevent antibody-mediated (AMR) and cell-mediated rejection (CMR) in presensitized murine recipients of life-supporting kidney allografts. To mimic the urgent clinical features of AMR experienced by presensitized patients, we designed a murine model in which BALB/c recipients were presensitized with fully MHC-mismatched C3H donor skin grafts one week prior to C3H kidney transplantation. Presensitized recipients demonstrated high levels of circulating and intragraft antidonor antibodies and terminal complement activity, rejecting grafts within 8.5 +/- 1.3 days. Graft rejection was predominantly by AMR, characterized by interstitial hemorrhage, edema and glomerular/tubular necrosis, but also demonstrated moderate cellular infiltration, suggesting CMR involvement. Subtherapeutic treatment with cyclosporine (CsA) and LF15-0195 (LF) did not significantly delay rejection. Significantly, however, the addition of anti-C5 mAb to this CsA/LF regimen prevented terminal complement activity and inhibited both AMR and CMR, enabling indefinite (>100 days) kidney graft survival despite the persistence of antidonor antibodies. Long-term surviving kidney grafts expressed the protective proteins Bcl-x(S/L) and A-20 and demonstrated normal histology, suggestive of graft accommodation or tolerance. Thus, C5 blockade combined with routine immunosuppression offers a promising approach to prevent graft loss in presensitized patients.