Initiation Of Rejection Research Articles

Topical inhibition of T cell costimulatory pathways in draining lymph nodes may suppress allograft rejection

Topical immune suppression is an attractive and practical therapeutic option to prolong survival time of allografts, before the appearance of new agent with higher immunosuppressive efficacy and lower undesirable side effects. The initiation of rejection and outcome of allografts is principally mediated by alloantigen reactive T cells. The activation of T cells requires at least two signals, first is T-cell receptor signal and second is costimulatory signal. T cells that encounter antigen without the appropriate costimulatory signal become anergy or tolerance. Migration of alloantigen-bearing dendritic cells into the T-cell zone of secondary lymphoid tissues, which are essential for primary alloimmune responses, effectively induces T-cell activation and expansion with the presence of two signals. Draining lymph nodes are the promising targets for topical immune suppression, as disrupting lymphatic drainage from the transplanted graft to lymph nodes prevented rejection of skin allografts and lymphadenectomy prolong the survival time of skin and corneal allografts in experimental animals. Therefore, we hypothesize that inhibition of T cell costimulatory pathways in draining lymph nodes could impair the alloantigen-specific immune response and reduce systemic immunosuppressive drugs dose for allografts survival. Further investigations are required to identify most efficient way for draining lymph nodes transfer of costimulatory molecule gene or topical drug administration of costimulatory inhibitors to draining lymph nodes.

Long-term culture of islets abrogates cytokine-induced or lymphocyte-induced increase of antigen expression on beta cells.

Immunogenicity of a graft depends on its expression of major histocompatability complex (MHC) antigens and adhesion molecules and on the amount of intragraft leukocytes, the so-called passenger leukocytes. Although long-term culture reduces passenger leukocytes, permanent acceptance is not necessarily observed after allogeneic transplantation. Because little is known about antigen expression on the surface of islet cells after long-term culture of islets, we investigated whether antigen expression of pancreatic beta cells is influenced by long-term culture and whether long-term culture can counteract the increase of antigen expression induced by cytokines or by allogeneic lymphocytes. We also investigated whether long-term cultured islets were able to stimulate allogeneic lymphocytes to produce cytokines. Isolated LEW.1A (RT1a) rat islets of Langerhans were cultured for 14 and 28 days. Precultured and freshly-isolated islets were then incubated for 2 days with rat recombinant interferon (rIFN)-gamma (1,000 IU/mL), or were co-cultured for 4 days with LEW.1W (RT1u) splenic lymphocytes. Long-term culture significantly reduced CD45 leukocytes within the islets and decreased the amount of beta cells expressing intercellular adhesion molecule (ICAM)-1, whereas MHC antigen expression remained unchanged. After incubation of freshly isolated islets with IFN-gamma induction of MHC class II antigens on beta cells, an increase of MHC class I antigen density and an enhancement of ICAM-1+ beta cells were observed. Similar results were found after co-culturing with allogeneic lymphocytes. Using precultured islets, the induction of MHC class II on beta cells by IFN-gamma was still present but significantly lower and was absent after co-culture with allogeneic lymphocytes. Enhancement of ICAM-1+ beta cells by IFN-gamma or by allogeneic lymphocytes was markedly lowered because of preculturing. The proportion of MHC class I beta cells remained unchanged; however, antigen density of long-term cultured islets (28 days) could not be enhanced by allogeneic lymphocytes. Precultured islets were not able to stimulate allogeneic lymphocytes to produce and release normal amounts of cytokines (IFN-gamma or interleukin [IL]-2). In conclusion, in addition to reduction-depletion of passenger leukocytes, long-term culturing of islets also is able to counteract the IFN-gamma-induced or allogeneic lymphocyte-induced increase of antigen expression. Therefore, initiation of rejection and generation of cytotoxic cells might be altered or timely delayed when long-term cultured islets are transplanted. The variable and conflicting in vivo results after transplantation of long-term cultured islets might be explained by the possible indirect antigen presentation, which is not influenced by islet preculture.

Donor antigen is necessary for the prevention of chronic rejection in CTLA4Ig-treated murine cardiac allograft recipients.

Optimal activation of T cells requires two signals: antigen engagement through the T cell receptor and a costimulatory signal. Previous studies have shown that blockade of the CD28:B7 costimulatory pathway using the soluble fusion protein CTLA4Ig can prevent acute rejection of organ and tissue allografts; however, long-term engraftment has not been seen universally. This study was undertaken to define the role of donor antigen in inducing long-term allograft survival in CTLA4Ig-treated recipients. A murine cardiac allograft model was employed using BALB/c donors and C57BL/6 recipients. Additional donor antigen in the form of donor splenocytes was given at the time of transplantation. Recipients were treated with a single dose of CTLA4Ig 2 days after transplantation. We find that a single dose of CTLA4Ig prolongs cardiac allograft survival, but permanent engraftment is not observed unless the recipients receive an injection of donor-type splenocytes. Treatment of the donor cells with CTLA4Ig does not by itself prolong allograft survival, which indicates the need for systemic treatment of the recipient. Allografts from animals not receiving donor cells show classic histologic changes of chronic rejection, and most cease function from 1 to 4 months after transplantation. Lethal irradiation of the donor cells does not appreciably affect their ability to prevent late allograft loss. Donor cells are required to synergize with CTLA4Ig and prevent late cardiac allograft loss in the murine system. The fact that pretreatment of the donor cells alone is not effective suggests a role for antigen presentation by recipient antigen-presenting cells in the initiation of rejection. As lethal irradiation of the donor cells does not affect their ability to promote long-term engraftment, our data suggest that long-term microchimerism is not required to prevent chronic rejection in this model.

Interleukin-8 expression in patients after renal transplantation

Cellular invasion and cytokine release are important steps in the initiation of rejection. We studied the release of interleukin-8 (IL-8), a potent proinflammatory and chemotactic cytokine, and its prognostic significance in predicting rejection after renal transplantation. Serum and urine samples were analyzed with an IL-8-specific sandwich enzyme-linked immunosorbent assay. Biopsy tissue specimens (n = 20) were snap-frozen and examined with immunohistochemistry using two monoclonal antibodies against human IL-8 (4G9 and 2A8). Serum IL-8 measurements were of no value in predicting rejection due to low sensitivity (24%). In 45 biopsy-proven acute rejections (<2 months after transplantation), urinary IL-8 concentrations were elevated in 62% (298 ± 54 pg/mL; P < 0.01), preceding clinical diagnosis of rejection. After treatment, the IL-8 concentration in urine decreased back to normal (33 ± 4 pg/mL; P < 0.01). The highest urinary IL-8 concentrations were seen in patients with biopsy-proven rejection in combination with acute tubular necrosis (610 ± 150 pg/mL). This finding was independent of renal function and urinary volume. Only three of 15 rejection episodes in patients more than 2 months after transplantation showed an elevated IL-8 concentration in urine (94 ± 60 pg/mL). In 10 of 23 patients with infection, a significant increase of IL-8 in urine was observed as well (157 ± 67 pg/mL; P < 0.05). IL-8-positive staining was found within interstitial mononuclear cells of all biopsy specimens showing rejection. Additionally, the antibody 4G9 stained arteriolar smooth muscle and tubular cells. Interestingly, a few IL-8-positive cells were present in two donor kidneys before transplantation was performed; control tissue was negative. Further investigations are necessary to determine the clinical value of urinary IL-8 determinations in the diagnosis of rejection and to evaluate the role of IL-8 in the pathogenesis of acute allograft rejection.

The platelet-activating factor antagonist WEB 2170. Its beneficial effect on dog renal allograft survival.

Platelet-activating factor is a phospholipid mediator of inflammation produced both by inflammatory cells (e.g., basophils, neutrophils, monocytes, platelets) and endothelial cells (1); its production is stimulated by several cytokine mediators, including TNF. The role of PAF in allograft rejection includes increasing endothelial permeability leading to reduced blood flow and margination of leukocytes; recruitment of cells into the allograft at the initiation of rejection; and intercellular signaling within the graft (2–4). In vivo evidence of PAF's role in rejection comes from a rabbit model, where a sustained local release of PAF was observed during hyperacute renal allograft rejection, with associated platelet and neutrophil accumulation within 5 min of revascularization (5).

Intraoperative Course and Prognostic Significance of Endotoxin, Tumor Necrosis Factor-alpha and Interleukin-6 in Liver Transplant Recipients

Early events in reaction of the host immune system to an allograft were studied by intraoperative measurements of endotoxin (ET), tumor necrosis factor-alpha (TNF-α) and interleukin-6 (IL-6) in human liver transplantation. Blood samples were collected prior to operation, before clamping of the liver vessels, at the beginning and end of the anhepatic phase, and 5 and 30 min after recirculation. Diagnosis of rejection and infection in the graft recipients was established by assessment of spontaneous blastogenesis and T-lymphocyte subpopulations in addition to clinical symptoms and results from biopsies and blood chemistry. Of the 27 unmatched liver transplantations included in this study, 8 patients had infections in the first two postoperative weeks and 6 patients showed rejection of their grafts under antithymocyte globulin immunoprophylaxis. Endotoxin was transiently elevated in plasma in the anhepatic phase (2-fold in comparison to normal values) as expected for an accumulation of intestinederived endotoxin during clamping of liver vessels, but no correlation was found with TNF-α levels and specific post-transplant complications. All patients with rejections had high plasma levels of TNF-α immediately after recirculation (mean value 240 pg TNF-α/ml), in contrast to low TNF-α levels in graft recipients without complications or infections. These results indicate that the initiation of rejection in liver transplantation is associated with increased plasma concentrations of TNF-α. The measured TNF-α concentrations are adequate to promote the binding of lymphocytes to allograft endothelial tissue and/or to induce expression of MHC antigens in the graft. Subsequent viral or bacterial infections were preceded by high intraoperative plasma concentrations of interleukin-6 (mean value 1400 pg IL-6/ml). The correlations of rejection with high intraoperative TNF-α levels and of infection with those of IL-6 are statistically significant in Wilcoxon tests for the direct measurements and in Fisher's exact tests for positive test values, with limits of 90 pg/ml for TNF-α and 800 pg/ml for IL-6.

Initiation of rejection of established islet allografts by third-party thyroid allografts and splenic dendritic cells

Initiation of rejection of established islet allografts by third-party thyroid allografts and splenic dendritic cells

Virus-specific MHC-restricted T lymphocytes may initiate allograft rejection

The principal function of the immune system is to protect the host from infection. Thus, therapeutic manipulations of the immune system in the treatment of non-infectious diseases are associated with significant changes in the ability to deal with infection. This is clearly illustrated by allograft recipients who require substantial immunosuppression to prevent allograft rejection and in whom infection is a major source of mortality and morbidity. In addition, a further relationship between infection and immune responses has long been commented on in these patients, namely an association between episodes of infection and aUograft rejection 1-3. Although early reports documenting such an association mentioned various infections (e.g., influenza 2, upper respiratory tract infectionsa), subsequently most attention has centred on the possible role ofcytomegalovirus (CMV) infection in the initiation of rejection 4-7. Clearly infection in an immunosuppressed allograft recipient is a complex situation leading to many non-specific immunological changes each of which might be postulated to lead to rejection4'6; however, we are led by recent experimental evidence to suggest that the initiation of rejection may be directly linked to the specific immune response mounted against a particular infectious agent. Thus, we propose that allograft rejection is initiated by effector T lymphocytes whose primary specificity is for foreign antigens (those of the infecting agent) which they see in the context of self major histocompatibility complex (MHC) antigens [' self + X']: such effectors can mediate rejection because of their crossreactive recognition of allogenic MHC antigens ['non-self]. Thus, the effector T cells generated by an allograft recipient in response to a given infection may initiate graft rejection when the particular alloantigens which they also recognize are present on the allograft. Alloreactivity and immune responses to other antigens can be mediated by the same lymphocytes For twenty years, immunologists have puzzled over the ability of alloantigens to elicit powerful immune responses given the apparent biological irrelevance of such responses. Experiments