Evidence for a nonclassical pathway of graft rejection involving interleukin 5 and eosinophils

Solving the Conundrum of Eosinophils in Alloimmunity

Eosinophils are bone-marrow-derived granulocytes known for their ability to facilitate clearance of parasitic infections and their association with asthma and other inflammatory diseases. The purpose of this review is to discuss the currently available human observational and animal experimental data linking eosinophils to the immunologic response in solid organ transplantation. First, we present observational human studies that demonstrate a link between transplantation and eosinophils yet were unable to define the exact role of this cell population. Next, we describe published experimental models and demonstrate a defined mechanistic role of eosinophils in downregulating the alloimmune response to murine lung transplants. The overall summary of this data suggests that further studies are needed to define the role of eosinophils in multiple solid organ allografts and points to the possibility of manipulating this cell population to improve graft survival.

Peripheral blood eosinophilia as a marker of acute cellular rejection in lung transplant recipients

Previous studies in solid organ transplantation have shown a relationship between circulating eosinophil (EOS) counts and the presence of acute cellular rejection (ACR). However, the relationship between this potential biomarker and ACR in lung transplant (LTx) patients remains unclear.

OBJECTIVE

To assess the association between EOS and the presence of acute cellular rejection in lung transplant recipients.

MATERIALS AND METHODS

Retrospective study of 583 transbronchial biopsies (TBB) performed in 256 lung transplant patients between 2012 and 2018. We analyzed age, sex, underlying pathology, date of transplant, indications for TBB, presence and degree of ACR, and the simultaneous absolute and relative EOS.

RESULTS

ACR were observed in 170 of 583 TBB (29.2%). EOS in patients with ACR were higher than in patients without ACR (203.6 ± 248/mm³ vs 103.1 ± 153/mm³; p < 0.001). High levels of both absolute and relative EOS were associated with the presence of ACR regardless of the underlying disease (odds ratio [OR] 1.003; 95% confidence interval [CI], 1.002-1.004; OR 1.226; 95% CI, 1.120-1.342) and time after transplant (OR 1.003; 95% CI, 1.002-1.004 and OR 1.239; 95% CI, 1.132-1.356). Moreover, both absolute and relative EOS were strongly associated with moderate and severe grades of ACR (OR 3.55; 95% CI, 3.00-4.10 and OR 3.56; 95% CI, 3.00-4.12).

CONCLUSIONS

EOS are elevated in ACR, especially in moderate or severe ACR. Increased vigilance for ACR is therefore advisable in lung transplant recipients with elevated EOS.

Programmed T cell differentiation: Implications for transplantation

While T cells play a critical role in protective immunity against infection, they are also responsible for graft rejection in the setting of transplantation. T cell differentiation is regulated by both intrinsic transcriptional pathways as well as extrinsic factors such as antigen encounter and the cytokine milieu. Herein, we review recent discoveries in the transcriptional regulation of T cell differentiation and their impact on the field of transplantation. Recent studies uncovering context-dependent differentiation programs that differ in the setting of infection or transplantation will also be discussed. Understanding the key transcriptional pathways that underlie T cell responses in transplantation has important clinical implications, including development of novel therapeutic agents to mitigate graft rejection.

Eosinophils promote inducible NOS-mediated lung allograft acceptance

Lungs allografts have worse long-term survival compared with other organ transplants. This is most likely due to their unique immunoregulation that may not respond to traditional immunosuppression. For example, local NO generation by inducible NOS (iNOS) is critical for lung allograft acceptance but associates with rejection of other solid organs. The source of NO in accepting lung allografts remains unknown. Here, we report that, unlike the case for other pulmonary processes in which myeloid cells control NO generation, recipient-derived eosinophils play a critical and nonredundant role in iNOS-mediated lung allograft acceptance. Depletion of eosinophils reduces NO levels to that of recipients with global deletion of iNOS and leads to a costimulatory blockade-resistant form of rejection. Furthermore, NO production by eosinophils depends on Th1 polarization by inflammatory mediators, such as IFN-γ and TNF-α. Neutralization of such mediators abrogates eosinophil suppressive capacity. Our data point to what we believe to be a unique and previously unrecognized role of eosinophil polarization in mediating allograft tolerance and put into perspective the use of high-dose eosinophil-ablating corticosteroids after lung transplantation.

The mechanisms of rejection in solid organ transplantation

Organ transplantation represents the preferred treatment option for many patients in terminal organ failure. The half-life of transplanted organs, however, is still far from being satisfactory with the vast majority of the organs failing within the first two decades following transplantation. At this stage, it has become apparent that rejection (prevalently mediated by humoral events) remains the primary cause of graft loss after the first year. In this light, studies are underway to better comprehend the immune events underlying graft rejection and novel immunosuppressive strategies are being explored. In this context, therapeutic apheresis techniques, that include therapeutic plasma exchange (TPE), immunoadsorption (IA) and extracorporeal photochemotherapy (ECP), represent an important adjunct in the current immunosuppressive armamentarium. This article briefly reviews our current understanding of the immune process underlying rejection of a solid organ transplant and describes the principal areas of application of therapeutic apheresis techniques in transplantation.

Double deficiency for RORγt and T-bet drives Th2-mediated allograft rejection in mice

Although Th1, Th2, and Th17 cells are thought to be major effector cells in adaptive alloimmune responses, their respective contribution to allograft rejection remains unclear. To precisely address this, we used mice genetically modified for the Th1 and Th17 hallmark transcription factors T-bet and RORγt, respectively, which allowed us to study the alloreactive role of each subset in an experimental transplant setting. We found that in a fully mismatched heterotopic mouse heart transplantation model, T cells deficient for T-bet (prone to Th17 differentiation) versus RORγt (prone to Th1 differentiation) rejected allografts at a more accelerated rate, indicating a predominance of Th17- over Th1-driven alloimmunity. Importantly, T cells doubly deficient for both T-bet and RORγt differentiated into alloreactive GATA-3-expressing Th2 cells, which promptly induced allograft rejection characterized by a Th2-type intragraft expression profile and eosinophilic infiltration. Mechanistically, Th2-mediated allograft rejection was contingent on IL-4, as its neutralization significantly prolonged allograft survival by reducing intragraft expression of Th2 effector molecules and eosinophilic allograft infiltration. Moreover, under IL-4 neutralizing conditions, alloreactive double-deficient T cells upregulated Eomesodermin (Eomes) and IFN-γ, but not GATA-3. Thus, in the absence of T-bet and RORγt, Eomes may salvage Th1-mediated alloimmunity that underlies IL-4 neutralization-resistant allograft rejection. We summarize that, whereas Th17 cells predictably promote allograft rejection, IL-4-producing GATA-3(+) Th2 cells, which are generally thought to protect allogeneic transplants, may actually be potent facilitators of organ transplant rejection in the absence of T-bet and RORγt. Moreover, Eomes may rescue Th1-mediated allograft rejection in the absence of IL-4, T-bet, and RORγt.

Innate immune cells in liver inflammation

Innate immune system is the first line of defence against invading pathogens that is critical for the overall survival of the host. Human liver is characterised by a dual blood supply, with 80% of blood entering through the portal vein carrying nutrients and bacterial endotoxin from the gastrointestinal tract. The liver is thus constantly exposed to antigenic loads. Therefore, pathogenic microorganism must be efficiently eliminated whilst harmless antigens derived from the gastrointestinal tract need to be tolerized in the liver. In order to achieve this, the liver innate immune system is equipped with multiple cellular components; monocytes, macrophages, granulocytes, natural killer cells, and dendritic cells which coordinate to exert tolerogenic environment at the same time detect, respond, and eliminate invading pathogens, infected or transformed self to mount immunity. This paper will discuss the innate immune cells that take part in human liver inflammation, and their roles in both resolution of inflammation and tissue repair.

Innate immunity and resistance to tolerogenesis in allotransplantation

The development of immunosuppressive drugs to control adaptive immune responses has led to the success of transplantation as a therapy for end-stage organ failure. However, these agents are largely ineffective in suppressing components of the innate immune system. This distinction has gained in clinical significance as mounting evidence now indicates that innate immune responses play important roles in the acute and chronic rejection of whole organ allografts. For instance, whereas clinical interest in natural killer (NK) cells was once largely confined to the field of bone marrow transplantation, recent findings suggest that these cells can also participate in the acute rejection of cardiac allografts and prevent tolerance induction. Stimulation of Toll-like receptors (TLRs), another important component of innate immunity, by endogenous ligands released in response to ischemia/reperfusion is now known to cause an inflammatory milieu favorable to graft rejection and abrogation of tolerance. Emerging data suggest that activation of complement is linked to acute rejection and interferes with tolerance. In summary, the conventional wisdom that the innate immune system is of little importance in whole organ transplantation is no longer tenable. The addition of strategies that target TLRs, NK cells, complement, and other components of the innate immune system will be necessary to eventually achieve long-term tolerance to human allograft recipients.

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.

Sequential evolution of IL-17 responses in the early period of allograft rejection

In addition to CD4+CD25+Foxp3+ regulatory T (T(reg)) cells which protect against autoimmune tissue injury, IL-17-producing CD4+ T (T(h)17) cells have been recently described and shown to play a crucial role in autoimmune injury. It appears that there is a reciprocal developmental pathway between T(h)17 and T(reg) cells. Although IL-17 is known to be associated with allograft rejection, the cellular source of IL-17 and the nature of T(h)17 in the context of allograft rejection remain unknown. In the current study, the dynamics of T(reg) and IL-17-producing cells after syngeneic and allogeneic transplantation were examined using a wild-type murine cardiac transplantation model. Ly6G+ cells were found to produce IL-17 during the early postoperative period and CD8+ as well as CD4+ T cells were also found to produce IL-17 during alloimmune response. Graft-infiltrating Ly6G+, CD4+, and even CD8+ cells were found to express IL-17 highly compared to those in spleen. Although the frequencies of T(h)17 and T(reg) were found to gradually increase in both syngeneic and allogeneic recipients, T(h)17/T(reg) ratios were significantly higher in recipients with allograft rejection than in syngeneic recipients. In conclusion, IL-17 is produced by neutrophils during the early postoperative period and subsequently by T(h)17 and CD8+ T cells during allograft rejection. T(h)17/T(reg) imbalance is associated with the development of allograft rejection. This study would provide basic information on T(h)17 biology for future investigation in the field of transplantation.

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.

CD8+ Th17 mediate costimulation blockade-resistant allograft rejection in T-bet-deficient mice

While studying Th responses induced by cardiac transplantation, we observed that mice deficient in the Th1 transcription factor T-bet (T-bet(-/-)) mount both Th1 and Th17 responses, whereas wild-type recipients mount only Th1 responses. Cells producing both IFN-gamma and IL-17 were readily detectable within the rejecting graft of T-bet(-/-) recipients, but were absent from the spleen, indicating that the in vivo microenvironment influences Th function. In addition, disrupting CD40-CD40L costimulatory interactions was highly effective at prolonging allograft survival in WT mice, but ineffective in T-bet(-/-) recipients. In this study, we report that CD8(+) Th17 mediate costimulation blockade-resistant rejection in T-bet(-/-) allograft recipients. Depleting CD8(+) cells or neutralizing IL-17 or the Th17-inducing cytokine IL-6 ablated the Th17 response and reversed costimulation blockade-resistant graft rejection. Neutralizing IL-4 in IFN-gamma(-/-) allograft recipients did not induce Th17, suggesting that T-bet, rather than IL-4 and IFN-gamma (known inhibitors of Th17), plays a critical role in negatively regulating Th17 in the transplant setting.

Transplant acceptance following anti-CD4 versus anti-CD40L therapy: evidence for differential maintenance of graft-reactive T cells

Inductive therapy with anti-CD4 or anti-CD40L monoclonal antibodies (mAb) leads to long-term allograft acceptance but the immune parameters responsible for graft maintenance are not well understood. This study employed an adoptive transfer system in which cells from mice bearing long-term cardiac allografts following inductive anti-CD4 or anti-CD40L therapy were transferred into severe combined immunodeficiency (SCID) allograft recipients. SCID recipients of cells from anti-CD4-treated mice (anti-CD4 cells) did not reject allografts while those receiving cells from anti-CD40L-treated mice (anti-CD40L cells) did reject allografts. Carboxyfluorescein succinimidyl ester (CFSE) labeling of transferred cells revealed that this difference was not associated with differential proliferative capacities of these cells in SCID recipients. Like cells from naïve mice, anti-CD40L cells mounted a Th1 response following transfer while anti-CD4 cells mounted a dominant Th2 response. Early (day 10) T-cell priming was detectable in both groups of primary allograft recipients but persisted to day 30 only in recipients treated with anti-CD4 mAb. Thus, anti-CD40L therapy appears to result in graft-reactive T cells with a naïve phenotype while anti-CD4 therapy allows progression to an altered state of differentiation. Additional data herein support the notion that anti-CD40L mAb targets activated, but not memory, cells for removal or functional silencing.

Liver eosinophilic infiltrate is a significant finding in patients with chronic hepatitis C

Eosinophilic infiltrate of liver tissue is described in primary cholestatic diseases, hepatic allograft rejection and drug-induced liver injury, but its significance and its implications in chronic hepatitis C are unknown. The aim of this study was to investigate the clinical significance of eosinophilic liver infiltrate in patients with chronic hepatitis C. We retrospectively evaluated 147 patients with chronic hepatitis C. The presence of eosinophilic infiltrate was investigated in liver biopsies, and a numeric count of eosinophilic leucocytes in every portal tract was assessed. An eosinophilic infiltrate of liver tissue (> or =3 cells evaluated in the portal / periportal spaces) was observed in 46 patients (31%), and patients who consumed drugs had an odds ratio (OR) of 4.02 (95% CI: 1.62-9.96) to have an eosinophilic infiltrate in liver biopsy. By logistic regression analysis, the presence of steatosis was independently associated with eosinophilic infiltrate (OR 5.86; 95% CI: 2.46-13.96) and homeostasis model assessment-score (OR 1.18; 95% CI: 1.00-1.39). Logistic regression analysis also showed that fibrosis staging > or = 2 by Scheuer score was associated with grading >1 by Scheuer score (OR 6.82; 95% CI 2.46-18.80) and eosinophilic infiltrate (OR 4.00; 95% CI 1.23-12.91). In conclusion, we observed that the eosinophilic infiltrate of liver tissue was significantly more frequent in patients who assumed drugs, and found a significant association between eosinophilic infiltrate, liver steatosis and liver fibrosis. These preliminary data could lead to a constant assumption of drugs as a co-factor of eosinophils-mediated liver injury in chronic hepatitis C.

Hepatic NKT cells: friend or foe?

The innate immune system represents a critical first line of host response to infectious, injurious and inflammatory insults. NKT cells (natural killer T-cells) are an important, but relatively poorly understood, component of the innate immune response. Moreover, NKT cells are enriched within the liver, suggesting that within the hepatic compartment NKT cells probably fulfil important roles in the modulation of the immune response to infection or injury. NKT cells are characterized by their rapid activation and secretion of large amounts of numerous types of cytokines, including those within the Th1-type, Th2-type and Th17-type groups, which in turn can interact with a multitude of other cell types within the liver. In addition, NKT cells are capable of participating in a wide array of effector functions with regards to other cell types via NKT cell-surface-molecule expression [e.g. FASL (FAS ligand) and CD40L (CD40 ligand)] and the release of mediators (e.g. perforin and granzyme) contained in cellular granules, which in turn can activate or destroy other cells (i.e. immune or parenchymal cells) within the liver. Given the huge scope of potential actions that can be mediated by NKT cells, it has become increasingly apparent that NKT cells may fulfil both beneficial (e.g. clearance of virally infected cells) and harmful (e.g. induction of autoimmunity) roles in the setting of liver disease. This review will outline the possible roles which may be played by NKT cells in the setting of specific liver diseases or conditions, and will discuss the NKT cell in the context of its role as either a ‘friend’ or a ‘foe’ with respect to the outcome of these liver disorders.

Blood eosinophilia as a marker of favorable outcome after allogeneic stem cell transplantation

Eosinophilia is observed in a variety of disorders including acute and chronic graft-versus-host disease (GVHD). The clinical records of 237 patients who underwent allogeneic stem cell transplantation (allo-SCT) were retrospectively reviewed. Eosinophilia, defined as a relative eosinophil count>4% within the first 100 days, was observed in 135 patients (57%). The incidence of grades II-IV acute GVHD was significantly higher in patients without eosinophilia than in those with eosinophilia (68% vs. 43%; P<0.001). The incidence of chronic GVHD was significantly higher in patients without eosinophilia than in those with eosinophilia (73% vs. 56%; P=0.011). Relapse rate was similar between patients with and without eosinophilia (33% vs. 27%; P=0.438). The probability of nonrelapse mortality was 10% in patients with eosinophilia, which was significantly lower than that in patients without eosinophilia (31%; P<0.001), and the overall survival (OS) at 3 years was 67% in patients with eosinophilia, which was significantly higher than that in patients without eosinophilia (51%; P=0.003). Multivariate analysis identified older age, high-risk disease, acute GVHD, sex disparity between patient and donor, and the absence of eosinophilia as significant factors for reduced OS. These data lead us to conclude that eosinophilia after allo-SCT may serve as a favorable prognostic marker.

Cutting edge: atopy promotes Th2 responses to alloantigens and increases the incidence and tempo of corneal allograft rejection

A large body of evidence suggests that corneal allograft rejection is mediated by a type 1 Th cell response and that deviation toward type 2 immunity favors graft survival. However, clinical observations indicate that patients with severe ocular allergies have increased risk of corneal allograft rejection. We used a mouse model of atopic conjunctivitis to evaluate the effects of Th2 immune deviation on corneal allograft survival and possible mechanisms of graft rejection. Our results reveal the following novel findings: 1) atopic conjunctivitis promotes systemic Th2 immune responses to corneal graft donor alloantigens; 2) corneal allografts in atopic host eyes have an increased incidence and swifter tempo of rejection; 3) increased rejection is associated with alterations in systemic T cell-mediated responses to donor alloantigens; and 4) corneal allograft rejection in atopic hosts does not require the direct involvement of infiltrating eosinophils.

Effector mechanisms in transplant rejection

Antigens, provided by the allograft, trigger the activation and proliferation of allospecific T cells. As a consequence of this response, effector elements are generated that mediate graft injury and are responsible for the clinical manifestations of allograft rejection. Donor-specific CD8+ cytotoxic T lymphocytes play a major role in this process. Likewise, CD4+ T cells mediate delayed-type hypersensitivity responses via the production of soluble mediators that function to further activate and guide immune cells to the site of injury. In addition, these mediators may directly alter graft function by modulating vascular tone and permeability or by promoting platelet aggregation. Allospecific CD4+ T cells also promote B-cell maturation and differentiation into antibody-secreting plasma cells via CD40-CD40 ligand interactions. Alloantibodies that are produced by these B cells exert most of their detrimental effects on the graft by activating the complement cascade. Alternatively, antibodies can bind Fc receptors on natural killer cells or macrophages and cause target cell lysis via antibody-dependent cell-mediated cytotoxicity. In this review, we discuss these major effector pathways, focusing on their role in the pathogenesis of allograft rejection.

Critical role of interleukin 5 and eosinophils in concanavalin A-induced hepatitis in mice

BACKGROUND & AIMS

Eosinophils are observed in several liver diseases, but their contribution in the pathogenesis of these disorders remains poorly investigated. Concanavalin A (Con A)-induced hepatitis is an experimental model of immune-mediated liver injury in which natural killer T (NKT) cells play a critical role through the production of interleukin (IL)-4 and the expression of Fas ligand (FasL). Because activated NKT cells also produce IL-5, a critical cytokine for eosinophil maturation and function, the role of IL-5 was investigated in this model.

METHODS

IL-5-deficient mice, eosinophil depletion in wild-type (WT) mice, and NKT cell transfer from WT- or IL-5-deficient mice into NKT cell-deficient mice were used to assess the role of IL-5 and eosinophils.

RESULTS

Liver eosinophil infiltrate and IL-5 production were observed after Con A challenge. Liver injury was dramatically reduced in IL-5-deficient or eosinophil-depleted mice. In addition, residual hepatitis observed in Fas-deficient mice was abolished after IL-5 neutralization. Finally, we showed that NKT cells constituted a critical source of IL-5. Indeed, transfer of WT NKT cells to mice lacking NKT cells restored liver injury, whereas transfer of IL-5-deficient NKT cells did not.

CONCLUSIONS

These observations highlight the pathologic role of IL-5 and eosinophils in experimental immune-mediated hepatitis.

Multiple pathways to allograft rejection

Allograft rejection results from a complex process involving both the innate and acquired immune systems. The innate immune system predominates in the early phase of the allogeneic response, during which chemokines and cell adhesion play essential roles, not only for leukocyte migration into the graft but also for facilitating dendritic and T-cell trafficking between lymph nodes and the transplant. This results in a specific and acquired alloimmune response mediated by T cells. Subsequently, T cells and cells from innate immune system function synergistically to reject the allograft through nonexclusive pathways, including contact-dependent T cell cytotoxicity, granulocyte activation by either Th1 or Th2 derived cytokines, NK cell activation, alloantibody production, and complement activation. Blockade of individual pathways generally does not prevent allograft rejection, and long-term allograft survival is achieved only after simultaneous blockade of several of them. In this review, we explore each of these pathways and discuss the experimental evidence highlighting their roles in allograft rejection.

A role for eosinophils in transplant rejection

Eosinophils release inflammatory mediators and cationic proteins that are instrumental in the pathogenesis of allergic diseases such as bronchial asthma. Here, we review experimental observations indicating that eosinophils are also involved in the rejection of allografts. We propose that their role as effectors of transplant damage becomes crucial when classical pathways of rejection are inhibited and T helper 2 (Th2) cells dominate the alloimmune response.

Sequential monitoring of peripheral T-lymphocyte cytokine gene expression in the early post renal allograft period

BACKGROUND

Despite numerous studies, the precise role of cytokines in acute renal allograft rejection remains unclear. In this study we have monitored sequential changes in peripheral T cell cytokine gene expression, correlating the changes with clinical events after adult renal transplantation, to provide a deeper insight of the role of cytokines in allograft rejection.

METHODS

Sequential changes in peripheral Th-1 [interleukin- (IL) 2 and interferon-gamma] and Th-2 (IL-4, IL-5, IL-10, and IL-13) cytokine gene expression in 43 patients with (n=15) and without (n=28) episodes of biopsy-proven rejection was monitored in the first 6 weeks after renal transplantation using a sensitive, semi-quantitative reverse-transcriptase polymerase chain reaction ELISA approach.

RESULTS

Th-2 cytokines: IL-5 and IL13 expression increased before and during acute rejection, and decreased after successful antirejection therapy. A significant fall in IL-4 expression after transplantation and subsequent return to its baseline level of expression was observed in both nonrejectors and rejectors. IL-10 showed persistently high expression in nonrejectors, but in rejectors the expression fell during acute rejection, with a subsequent rise after antirejection therapy. Th-1 cytokines: IL-2 and IFN-gamma decreased in expression in the first week posttransplant in the rejectors, at the time of acute rejection (IL-2 only) and immediately after completion of antirejection therapy.

CONCLUSIONS

Sequential monitoring of peripheral T cell cytokine gene expression after renal transplantation detected changes in expression that correlated with episodes of acute rejection and response to antirejection therapy. This approach may be applicable in the clinical laboratory for monitoring posttransplant changes in T cell alloreactivity and immunosuppression.

Immunobiology of allograft rejection in the absence of IFN-gamma: CD8+ effector cells develop independently of CD4+ cells and CD40-CD40 ligand interactions

Both wild-type (WT) and IFN-gamma-deficient (IFN-gamma(-/-)) C57BL/6 mice can rapidly reject BALB/c cardiac allografts. When depleted of CD8(+) cells, both WT and IFN-gamma(-/-) mice rejected their allografts, indicating that these mice share a common CD4-mediated, CD8-independent mechanism of rejection. However, when depleted of CD4(+) cells, WT mice accepted their allografts, while IFN-gamma(-/-) recipients rapidly rejected them. Hence, IFN-gamma(-/-), but not WT mice developed an unusual CD8-mediated, CD4-independent, mechanism of allograft rejection. Allograft rejection in IFN-gamma(-/-) mice was associated with intragraft accumulation of IL-4-producing cells, polymorphonuclear leukocytes, and eosinophils. Furthermore, this form of rejection was resistant to treatment with anti-CD40 ligand (CD40L) mAb, which markedly prolonged graft survival in WT mice. T cell depletion studies verified that anti-CD40L treatment failed to prevent CD8-mediated allograft rejection in IFN-gamma(-/-) mice. However, anti-CD40L treatment did prevent CD4-mediated rejection in IFN-gamma(-/-) mice, although grafts were eventually rejected when CD8(+) T cells repopulated the periphery. The IL-4 production and eosinophil influx into the graft that occurred during CD8-mediated rejection were apparently epiphenomenal, since treatment with anti-IL-4 mAb blocked intragraft accumulation of eosinophils, but did not interfere with allograft rejection. These studies demonstrate that a novel, CD8-mediated mechanism of allograft rejection, which is resistant to experimental immunosuppression, can develop when IFN-gamma is limiting. An understanding of this mechanism is confounded by its association with Th2-like immune events, which contribute unique histopathologic features to the graft but are apparently unnecessary for the process of allograft rejection.

Eosinophil-induced liver injury: an experimental model using IL-5 transgenic mice

BACKGROUND/AIMS

In certain liver diseases, activated eosinophils are considered to be important effector cells in addition to T-cell-mediated cytotoxicity. No experimental model, however, has been developed for in vivo analysis of the cytotoxic mechanisms.

METHODS

Interleukin-5 (IL-5) transgenic mice (C3H/HeN-TgN(IL-5)Imeg), which exhibit marked eosinophilia without liver injury, were injected once with 25 microg of lipopolysaccharide (LPS) intraperitoneally. The mice were sacrificed weekly and eosinophilic injuries were assessed microscopically. To clarify the role of Kupffer cells and tumor necrosis factor-alpha (TNF-alpha) in the liver injury, gadolinium chloride (GdCl3) and anti-TNF-alpha neutralizing antibody were administrated before the LPS injection.

RESULTS

Two weeks after injection, transgenic mice exhibited marked infiltration of eosinophils and extensive lobular necrosis. Transmigration of eosinophils through vascular endothelium and degranulation of eosinophil cytotoxic granules in inflamed areas were observed. These eosinophilic injuries were transient, but liver-specific. Pre-administration of GdCl3 and anti-TNF-alpha markedly reduced the hepatic inflammation, suggesting that LPS-activated Kupffer cells play a key role in producing the cytotoxicity of eosinophils by releasing TNF-alpha.

CONCLUSIONS

We have established an experimental model of eosinophil-induced liver injury using IL-5 transgenic mice. Since this model is simple and highly reproducible, it will be useful for analysis of in vivo cytotoxic mechanisms of eosinophils.

IL-5 Mediates Eosinophilic Rejection of MHC Class II-Disparate Skin Allografts in Mice

CD4 T cells play a crucial role in the acute rejection of MHC class II-disparate skin allografts, mainly by Fas/Fas ligand-mediated cytotoxicity. Because recent observations indicate that eosinophils may be found within allografts rejected by CD4 T cells, we evaluated the role played by IL-5, the main eosinophil growth factor, and by eosinophils in the rejection of MHC class II-disparate skin grafts. C57BL/6 mice rapidly rejected MHC class II-disparate bm12 skin grafts. Rejected skins contained a dense, aggressive eosinophil infiltrate. Lymphocytes isolated from lymph nodes draining rejected bm12 skin were primed for IL-5 secretion, and IL-5 mRNA was present within rejected grafts. The IL-5/eosinophil pathway played an effector role in allograft destruction, because the rejection of bm12 skin was significantly delayed in IL-5-deficient mice as compared with wild-type animals. The role of the IL-5/eosinophil pathway was further investigated in MHC class II-disparate donor-recipient strains unable to establish Fas/Fas ligand interactions. Fas ligand-deficient gld/gld mice rejected bm12 skins, and bm12 mice rejected Fas-deficient lpr/lpr C57BL/6 skins. Neutralization of IL-5 prevented acute rejection in both combinations. We conclude that MHC class II-disparate skin allografts trigger an IL-5-dependent infiltration of eosinophils that is sufficient to result in acute graft destruction.

Critical roles for IL-4, IL-5, and eosinophils in chronic skin allograft rejection

C57BL/6 mice injected with the 145-2C11 anti-CD3 mAb and grafted with MHC class II disparate bm12 skin develop a chronic rejection characterized by interstitial dermal fibrosis, a marked eosinophil infiltrate, and an obliterative intimal vasculopathy. Because these changes occur in the absence of alloreactive antibodies, we examined the contribution of cytokines in their pathogenesis. Chronically rejected grafts showed a marked accumulation of both IL-4 and IL-5 mRNA. Mixed lymphocyte reaction experiments established that mice undergoing chronic rejection were primed for IL-4, IL-5, and IL-10 secretion. In vivo administration of anti-IL-4 mAb completely prevented allograft vasculopathy as well as graft eosinophil infiltration and dermal fibrosis. Injection of anti-IL-5 mAb or the use of IL-5-deficient mice as recipients also resulted in the lack of eosinophil infiltration or dermal fibrosis, but these mice did develop allograft vasculopathy. Administration of anti-IL-10 mAb did not influence any histologic parameter of chronic rejection. Thus, in this model, IL-4- and IL-5-mediated tissue allograft eosinophil infiltration is associated with interstitial fibrosis. IL-4, but not eosinophils, is also required for the development of obliterative graft arteriolopathy.

Immune mechanisms associated with the rejection of fetal murine proislet allografts and pig proislet xenografts: comparison of intragraft cytokine mRNA profiles

BACKGROUND

Previous in vivo depletion studies of CD4 and CD8 T cells indicated that different rejection mechanisms operate for proislet allografts and xenografts. The cellular and molecular mechanisms of acute proislet allograft and xenograft rejection have therefore been characterized and directly compared.

METHODS

The intragraft cytokine mRNA profile in rejecting BALB/c (H-2d) proislet allografts was analyzed in control, CD4 T cell-depleted, and CD8 T cell-depleted CBA/H (H-2k) recipient mice using semi-quantitative reverse transcriptase-assisted polymerase chain reaction (RT-PCR). The cytokine profiles for proislet allografts and pig proislet xenografts at 3-10 days posttransplant were directly compared and correlated with graft histopathology.

RESULTS

Allograft rejection was protracted (2-3 weeks), characterized by infiltrating CD8 T cells and CD4 T cells (no eosinophils) and was associated with a Th1-type CD4 T cell response (IL-2, IFN-gamma, and IL-3 mRNA) and a CD8 T cell-dependent spectrum of cytokine gene expression (IL-2, IFN-gamma, IL-3, and IL-10 mRNA). Xenograft rejection was rapid (6-8 days), involved predominantly CD4 T cells and eosinophils, and in contrast to allografts, exhibited intragraft mRNA expression for the Th2 cytokines IL-4 and IL-5.

CONCLUSIONS

Proislet allograft and xenograft rejection differ in the tempo of destruction, phenotype of the cellular response and intragraft profile of cytokine mRNA. The recruitment of eosinophils only to the site of xenorejection correlates with IL4 and IL-5 mRNA expression. These findings suggest that different anti-rejection strategies may need to be developed to optimally target the allograft and the xenograft response.

Chronic rejection of major histocompatibility complex class II-disparate skin grafts after anti-CD3 therapy: a model of antibody-independent transplant vasculopathy

BACKGROUND

Chronic rejection remains a leading cause of allograft loss. Histologically, it is characterized by arterial intimal thickening and parenchymal fibrosis. The immune mechanisms triggering chronic rejection are still uncompletely understood.

METHODS

We performed major histocompatibility complex (MHC) class H-incompatible skin grafts from C-H2bm12 (bm12, H2bm12) into C57BL/6 (C57BL/6, H2b) recipients immunosuppressed with a short course of anti-CD3 monoclonal antibodies to prevent acute rejection.

RESULTS

More than 80% of grafts survived for prolonged periods, but eventually all displayed macroscopic and microscopic evidence of chronic rejection. At histology, there was a progressive arterial intimal thickening as well as intense dermal fibrosis. This was accompanied by an inflammatory infiltrate consisting of lymphocytes and macrophages, but also of a considerable number of eosinophils. Mice with chronic rejection were unable to generate anti-donor MHC class II cytotoxic T lymphocyte activity at either 20 or 60 days after transplant. Furthermore, transplantation of bm12 skins on C57BL/6-congenic, Ig knock-out mice was associated with the development of a chronic rejection that was identical to that occurring in wild-type C57BL/6 animals, indicating that alloantibodies are not necessary in this model.

CONCLUSIONS

(1) Skin grafts may undergo chronic rejection with the characteristic lesions of vasculopathy and fibrosis; (2) chronic rejection of MHC class II-disparate skins may occur in the absence of direct cytotoxic T lymphocyte activity or alloantibodies.

Eosinophils in acute cellular rejection in liver allografts

Eosinophils have a role in various allergic and inflammatory disease processes and participate in the process of acute rejection in solid organ allografts. Initial studies described the diagnostic value of eosinophils in kidney allograft rejection. Graft eosinophilia is a sensitive and specific marker of acute rejection in liver allografts and has been incorporated as one of the diagnostic criteria of acute rejection by the Royal Free Hospital scoring system. Blood eosinophilia also has been investigated and is a useful diagnostic marker of acute rejection in liver and kidney allografts, although studies differ in defining the day of onset of eosinophilia in relation to rejection. Eosinophils probably act through the chemokines interleukin-5 and RANTES (regulated on activation, normal T cells expressed and secreted) in the pathogenesis of acute rejection. Basic cytotoxic proteins, such as eosinophil cationic protein and major basic protein, are released by the eosinophils, and their effector role in acute rejection has been studied through the use of specific monoclonal antibodies. Successful treatment of acute rejection with corticosteroids has been associated with a decrease in graft and blood eosinophil counts. Eosinophils also act as prognostic markers of acute rejection, as shown by studies reporting that patients with elevated eosinophil counts and steroid-resistant rejection showed a worse prognosis. Further research into the effector mechanisms of eosinophils in acute rejection needs to be performed. The ability of eosinophils to distinguish those diseases with different responses to standard immunosuppression and other diseases in the context of acute rejection also needs to be studied.

Cellular localization of interleukin-5 expression in rectal carcinoma with eosinophilia

Eosinophilia often occurs in malignant diseases. This report concerns a female patient aged 76 years, diagnosed with rectal carcinoma with eosinophilia. Sera were obtained at two different periods (at diagnosis and after the operation) for the evaluation of levels of interleukin-5 (IL-5). The serum IL-5 level increased to 264 pg/mL, and returned to an undetectable level after the operation. The serum at diagnosis enhanced the viability of normal eosinophils in vitro, and this activity was inhibited by antihuman IL-5 polyclonal antibody. Immunohistochemistry and in situ hybridization revealed that stromal eosinophils contained IL-5 protein and messenger RNA (mRNA), but no IL-5 transcripts were detected in eosinophils attached to carcinoma cells. In situ detection of apoptosis showed that several eosinophils attached to tumor cells underwent apoptosis and lost their eosinophil secreted cationic protein (ECP) and major basic protein (MBP). These results may suggest that activated eosinophils by IL-5 play an important role in host defense mechanisms, releasing their toxic granule proteins on adjoining tumor cells.

Tolerance and latent cellular rejection in long-term liver transplant recipients

Tolerance develops in a proportion of long-term liver transplant recipients but currently cannot be identified before an attempt at withdrawal from immunosuppression therapy. In the present study, we have examined the immunophenotypic characteristics of the cellular infiltrate in portal tracts and lobules as observed in liver biopsy specimens in relation to the outcome of subsequent withdrawal from immunosuppression therapy. Cryostat biopsy specimens from 27 long-term recipients before drug withdrawal, and from 10 patients with recent transplants who were having acute rejection, were analyzed. Immunohistochemical staining was performed for CD3+ (pan T cell), CD8+ (cytotoxic), CD4+ (helper), CD45RO+ (memory), CD45RA+ (naive), CD56+ (natural killer), CD68+ (macrophage), and CD8+ perforin+ cells. Fewer CD8+ and CD3+ cells were present in the lobular areas of biopsy specimens from patients who were successfully withdrawn from immunosuppression therapy (n = 6) compared with biopsy specimens from patients with nontolerant grafts (n = 9; 15 vs. 23 cells/high-power field [hpf] [P < .01] and 16 vs. 26 cells/hpf [P < .03], respectively) or biopsy specimens obtained during acute rejection (15 vs. 31 cells/hpf [P < .01] and 16 vs. 32 cells/hpf [P < .01]). Cell frequencies in the biopsy specimens of nontolerant long-term patients were similar to those found with acute rejection. Immunophenotyping the lobular inflammation within long-term liver allografts assists in identifying those patients in whom drug withdrawal is likely to be unsuccessful and in whom it is postulated a form of inactive, latent cellular rejection exists.

Eotaxin and capping protein in experimental vasculopathy

Ischemia-induced tissue activation may contribute to the pathogenesis of graft vasculopathy, but the mediators implicated have only partially been characterized. To gain further insight into the molecular mechanisms involved, syngeneic rat aortic transplants with cold-storage-induced vasculopathy were studied for differentially expressed mRNA transcripts. Vessel segments were exposed to either 1 or 18 hours of cold ischemia, followed by transplantation into syngeneic recipients. After 3 days or 4 weeks, the grafts were removed and total mRNA was isolated and used for differential display to identify modulation of transcript expression related to prolonged storage. Using 15 sets of random primers, 17 polymerase chain reaction products were up-regulated and 2 were downregulated in grafts exposed to 18 hours of ischemia. Sequencing of these amplicons showed that 6 had a high degree of homology to known sequences whereas 13 had no homology to any of the genes in the database. Two of the differentially displayed amplicons (capping protein and eotaxin) were cloned, re-amplified, and used as probes for Northern blot analysis to confirm their differential expression. Immunohistochemistry using monoclonal antibodies against capping protein-alpha and eotaxin confirmed that both proteins are expressed in the media of normal aortas and that there was an increased expression in vessels exposed to prolonged ischemia albeit that the increase at the protein level seemed less compared with changes in transcript expression. Northern blots with RNA from aortic allografts exposed to prolonged ischemic storage also showed increased levels of capping protein and eotaxin mRNA whereas there was a decrease in the relative amount of these transcripts in vessels exposed to balloon denudation, suggesting that the increase after prolonged ischemic exposure is not the result of a nonspecific response to injury. Based on the biological characteristics of capping protein and eotaxin it is conceivable that they play a pathogenetic role in ischemia-induced vessel wall remodeling. It remains to be established whether these genes or their products serve as target molecules for therapeutic interventions to prevent or treat cold-storage-induced graft vasculopathy.

Immune cholangitis: liver allograft rejection and graft-versus-host disease

A pronounced similarity exists between liver allograft rejection and graft-versus-host disease (GVHD) in the damage and eventual destruction of small intrahepatic bile ducts. Although an immunologic reaction has an important role, precisely identifying the target antigens or reason for persistence of the immune response has been difficult. An important difference between GVHD and liver rejection is the development of obliterative arteriopathy only in rejection. The three main histopathologic features of acute rejection are a predominantly mononuclear but mixed portal inflammation, subendothelial inflammation of portal or terminal hepatic veins (or both), and bile duct inflammation and damage. In acute rejection, a controversial issue is determining when therapeutic intervention is needed. The recommended approach is to base treatment on a combination of histopathologic changes and liver injury or dysfunction. Chronic rejection, which usually does not occur before 2 months after transplantation, is characterized by two main histopathologic features: (1) damage and loss of small bile ducts and (2) obliterative arteriopathy. Acute GVHD begins within the first month after transplantation and most commonly involves the skin, gastrointestinal tract, and liver, whereas chronic GVHD usually develops more than 80 to 100 days after liver transplantation and affects 30 to 50% of long-term survivors. Recognition of the early, cellular stages of chronic GVHD is important in preventing irreversible damage.

The role of cytokines during rejection of foetal pig and foetal mouse pancreas grafts in nonobese diabetic mice

The rejection of discordant foetal pig islet xenografts in nonimmunosuppressed nonobese diabetic (NOD) mice is dominated by polymorphonuclear cell infiltration whereas allografts are almost exclusively infiltrated by mononuclear cells. To determine if this variation is due to different proinflammatory factors generated at the graft site, we analysed graft-site mRNA expression of various cytokines, and the eosinophil attractant chemokine, eotaxin, in a renal subcapsular islet transplant model using organ cultured foetal pig (xenograft) and foetal BALB/c (allograft) pancreas in prediabetic NOD mice. Using semiquantitative RT-PCR on samples recovered at multiple time points during the first 15 post-transplantation days from mice transplanted with either allogeneic or xenogeneic tissue, we found increased expression of IL-2, IL-4. TNF-beta and IL-10 mRNAs at the peak of the cellular infiltrate (on day 5) in both xenografts and allografts but, in contrast to the allografts, no enhanced transcription of IFN-gamma mRNA in the rejecting xenografts. When an allograft and a xenograft were placed at the opposite pole of the same kidney the histological appearance of the rejecting allograft site resembled the xenograft site with significant numbers of eosinophils in both, and enhanced expression of eotaxin and iNOS. Additionally, the xenograft response, unlike the allograft response, was marked by an early increased expression of TNF-alpha and IL-S (day 3) and an almost complete absence of IFN-gamma expression. The results suggest a distinct cell-mediated mechanism for rejection of foetal pancrease xenografts compared to the rejection of foetal pancreas allografts.

Systemic administration of cellular interleukin-10 can exacerbate cardiac allograft rejection in mice

Cellular interleukin-10 (cIL-10) has been shown to inhibit cytokine production by T helper type 1 (Th1) cells by blocking antigen presenting cell function. This activity has suggested that IL-10 might be useful in the treatment of transplant rejection. Stimulatory effects of IL-10 however, have also been observed both on T and B cell differentiation. In this study, we examined the influence of recombinant (r) mouse (m) IL-10 on heterotopic vascularized heart allograft survival in the B10(H2b)-->C3H(H2k) strain combination that crosses both major histocompatibility complex (MHC) and non-MHC-histocompatibility antigen (non-MHC-HA) barriers. The influence of IL-10 was also examined in the B10.BR (H2k)--> C3H combination with disparity at only non-MHC-HA loci. Postoperative intraperitoneal administration of IL-10 (100 microg/d, days 0-6) significantly accelerated heart graft rejection both in the B10-->C3H (mean survival time [MST] 7.8+/-0.2 days; control MST 10.6+/-0.6 days; P<0.05) and the B10.BR-->C3H combination (MST 14.3+/-0.5 days; control MST 77.7+/-14.4 days). Ex vivo IL-10 perfusion of donor hearts for either 15 min or 2 hr did not affect subsequent graft survival. Immunologic monitoring of transplanted mice revealed that IL-10 treatment (100 microg/d, i.p., days 0-6) increased both the circulating complement-dependent cytotoxic (CDC) antibody titer and splenic anti-donor cytotoxic T lymphocyte (CTL) activity measured up to 3 weeks posttransplant. These findings indicate that post transplant systemic administration of cIL-10 can promote vascularized allograft rejection, and that this may reflect stimulation both of B and T cell alloimmune responses.

Production of IL-4 and IL-10 does not lead to immune quiescence in vascularized human organ grafts

The delineation of T helper cell subsets into T helper type 1 (Th1) and T helper type 2 (Th2) populations based on the production of specific cytokines has been useful in understanding the regulation and progression of immune-based pathologies. In order to test the relevance of this concept to human solid organ transplantation, in situ and system Th1 and Th2 cytokine profiles were characterized in liver allograft recipients. Bile and serum samples obtained posttransplant were analyzed for the cytokines IL-2, IFN-gamma, IL-4, and IL-10. Significant elevations of IL-4 and IL-10 were measured at the site of graft rejection. In contrast, IL-2, IFN-gamma, and IL-4 were markedly elevated in the circulation during rejection. Analyses of sequential bile samples revealed that Th1 and Th2 cytokines showed similar kinetics of production in response to alloantigen. Taken together, these results indicate that acute rejection of human allografts can proceed [correction of procede] in the presence of minimal levels of the Th1 cytokines IL-2 and IFN-gamma and high levels of IL-4 and IL-10.

Suppression of in vivo tumor growth by the transfection of the interleukin-5 gene into colon tumor cells

To investigate the influence of tumor producing interleukin-5 (IL-5) on growth kinetics of tumors, we transduced the murine IL-5 gene into murine colon C26 tumor cells. Two IL-5-secreting clones, low-level IL-5 producer C26-8B and high-level IL-5 producer C26-6F, were established. Both tumors, C26-6F and C26-8B, grew more slowly than the mock C26 tumor, although the in vitro growth rate of these IL-5 transfectants was much the same as that of the mock C26 cells. There was a significantly decreased number of colonies in the lung of mice given C26-6F or C26-8B tumors i.v. than in mice given mock C26 tumors i.v. Moreover, in mice given C26-6F cells i.v., a smaller number of tumor colonies in the lung was observed, as compared to the case with C26-6B cells. While the growth rate of C26-8B tumors in mice treated with anti-IL-5 mAb was more rapid than that seen in control mAb-treated mice, growth of C26-6F tumors in anti-IL-5-mAb-treated mice was slightly more rapid compared to findings in control mAb-treated mice. The isotype-matched mAb did not alter the in vitro growth of mock-C26 cells or of the IL-5-gene-modified C26 cells. Growth of IL-5-secreting C26 tumors transplanted in nude mice was also inhibited. These results suggest that tumor-producing IL-5 inhibits growth of colon tumors mediated through T-cell-independent protective mechanisms of the host.

Elevated biliary interleukin 5 as an indicator of liver allograft rejection

Interleukin 5 (IL-5) is a T cell-derived cytokine that acts as a potent and specific eosinophil differentiation factor in humans. During liver allograft rejection, intragraft IL-5 mRNA and eosinophilia have been observed. The objective of this study was to correlate the levels of IL-5 in bile and serum with eosinophilia and allograft rejection in paediatric liver recipients. IL-5 levels were determined by ELISA (enzyme-linked immunosorbent assay) in bile (n = 85) and serum (n = 106) and obtained prospectively from 15 patients during the first 3 weeks post-transplantation. Biliary and serum IL-5 levels were significantly elevated during allograft rejection compared to IL-5 levels when no rejection was apparent or during infectious complications. The highest IL-5 levels were measured in the bile during the early rejection period (3 days prior to biopsy-proven rejection). Fifteen of 16 rejection episodes were marked by increases in IL-5 as revealed by analysis of sequential samples from individual patients. In all patients with rejection, elevations in serum IL-5 were associated with elevations in peripheral eosinophil counts. These results indicate that IL-5 is produced in the liver and may be a useful and specific marker of allograft rejection. Furthermore, these findings provide further evidence for a pathway of liver allograft rejection mediated by IL-5 activated eosinophils.

Expression of the cytotoxic T cell mediator granzyme B during liver allograft rejection

Cytotoxic T lymphocytes (CTL) constitute a major component of the alloreactive response following organ transplantation. The molecular mechanisms of CTL killing remain to be determined but multiple candidate molecules involved in CTL-mediated cytotoxicity have been identified. Granzyme B, a serine protease, participates in perforin-dependent pathways of cytotoxicity and is necessary for induction of DNA fragmentation in target cells. In this study the expression of granzyme B in liver biopsies obtained from liver allograft recipients was determined by semiquantitative reverse transcriptase polymerase chain reaction. Biopsies were classified into four groups--no evidence of rejection, preservation injury, acute rejection, or resolving rejection--according to histopathological criteria. There was a significantly higher frequency of transcripts for granzyme B in the acute rejection group (82.8%) compared to the no rejection (20.0%), resolving rejection (12.5%) and preservation injury (0%) groups. Analysis of granzyme B gene expression in sequential samples from individual patients prior to, and after, treatment for rejection revealed an inverse correlation between granzyme B mRNA and response to treatment. These findings indicate that the cytopathic mediator granzyme B may participate in CTL-mediated cytotoxicity during liver allograft rejection.

The host response in experimental corneal xenotransplantation

In addressing the worldwide shortage of human donor cornea for transplantation, animal cornea may be a substitute if mechanisms of xenogeneic (cross-species) rejection can be identified and controlled. Xenotransplantation of solid organs is followed by hyperacute rejection with minutes due to humoral graft rejection. In an experimental model corneal xenografts in rats survived for 2-3 days, depending on the phylogenetic disparity of the donor animal. Endothelial injury was the specific cause of graft failure, probably mediated by humoral rejection mechanisms. A later cell-mediated rejection response was seen. The potent humoral response is the most important feature differentiating xenograft from allograft rejection.