MHC-identical heart and hepatocyte allografts evoke opposite immune responses within the same host.

Background. Purified allogeneic hepatocytes are highly antigenic and elicit immune responses that are not easily controlled. However, it is not clear whether hepatocytes are not capable of inducing protective immune mechanisms or whether they are not susceptible to protection by immune mechanisms that permit long-term survival of other allografts. The purpose of the current study was to determine whether donor-matched allogeneic hepatocytes are protected from rejection in mice that have been induced to accept heart allografts. Methods. Transient treatment with anti-CD4 monoclonal antibody (mAb) or gallium nitrate (GN) was used to induce acceptance of heterotopic FVB/N (H-2 q ) heart allografts by C57BL/6 (H-2 b ) mice. Transgenic hA1AT-FVB/N hepatocytes were sequentially transplanted into C57BL/6 mice that had accepted FVB/N heart allografts more than 60 days (heart acceptor mice), CD8 depleted C57BL/6 heart acceptor mice, or B-cell knockout (BCKO, H-2 b ) heart acceptor mice. Hepatocyte survival was determined by the detection of secreted transgenic product hAlAT by enzyme-linked immunosorbent assay (ELISA). Results. FVB/N hepatocytes were rejected by day 10-14 posttransplant, while FVB/N heart allografts continued to function in C57BL/6, BCKO, and CD8 depleted heart acceptor mice. When FVB/N hepatocytes and heart allografts were concurrently transplanted into C57BL/6 or BCKO mice under short-term cover of anti-CD4 mAb or GN, hepatocyte rejection occurred by day 10 posttransplant, while most heart allografts survived for more than 60 days. Conclusions. Hepatocyte rejection does not appear to interfere with the induction of mechanisms that permit heart allograft acceptance. However, immune responses to allogeneic hepatocytes are not susceptible to regulation by mechanisms induced in heart acceptor mice. The simultaneous rejection of FVB/N allogeneic hepatocytes and continued acceptance of FVB/N-matched heart allografts is independent of host CD8 + T cells and humoral immunity.