INTERFERON-GAMMA AND INTERLEUKIN-10 MESSENGER-RNA ARE UP-REGULATED AFTER ORTHOTOPIC LIVER-TRANSPLANTATION IN TOLERANT RATS - EVIDENCE FOR CYTOKINE-MEDIATED IMMUNE DYSREGULATION

Background. Immune regulation requires antigen recognition, signaling, activation, secretion of cytokines, and effector function by lymphocy tes. Although there is redundancy in the activation and function of th e immune response, some cytokines simultaneously promote and suppress different pathways of immunity. In the experiments reported here we co mpare cytokine gene expression within liver allografts from tolerant r ats with normal and isografted liver tissue. We also compare the secre tion of interferon-gamma (IFN-gamma) in the supernatant from mixed lym phocyte cultures by using peripheral blood lymphocytes stimulated agai nst donor antigen. Methods. Orthotopic liver transplantations were per formed using the cuff technique without hepatic artery revascularizati on. Nonisotopic in situ hybridization (ISH) was used to detect and loc alize messenger RNA to specific cells within tissue. Antisense DNA pro bes were generated to interleukin-2 (IL-2), IL-4, IL-10, and IFN-gamma . One-way mixed lymphocyte cultures were set up against irradiated don or splenocytes, and the supernatant was collected to measure IFN-gamma by enzyme-linked immunosorbent assay. Results. Expression of IFN-gamm a and IL-10 was up-regulated in tolerant animals versus normal or isog rafted liver (p = 0.0002 and 0.0001, IFN-gamma and IL-10, respectively ). In situ hybridization localized the expression of messenger RNA pre dominantly to the cytoplasm of the hepatocytes. Levels of IFN-gamma we re higher in the supernatant from proliferating peripheral lymphocytes against donor antigen from tolerant animals versus naive control anim als. Conclusions. Expression of IFN-gamma and IL-10 is up-regulated in hepatocytes from allograft tissue after orthotopic liver transplantat ion. We believe that the up-regulation of IL-10 cross-regulates the ef fector function of IFN-gamma and supports cytokine-mediated immune dys regulation, which may be a mechanism of tolerance after orthotopic liv er transplantation in rats.