Myocyte injury and contraction abnormalities produced by cytotoxic T lymphocytes

The mechanisms by which ventricular function is altered during cardiac transplant rejection are not well understood. Therefore, an in vitro model system has been developed to facilitate investigation of lymphocyte-mediated myocyte injury.

Splenic lymphoid cells were obtained from mice 8-10 days after placement of a vascularized abdominal cardiac allograft and were restimulated in vitro with irradiated donor-type splenocytes for 5 days. Cytotoxic effects of these allogenically stimulated lymphocytes on syngeneic and donor strain fetal cultured myocytes were determined by a 51Cr release assay at different lymphocyte to myocyte ratios. 51Cr release from donor strain myocytes was detectable within 1 hour of exposure, was maximal by 3-5 hours of coincubation with sensitized lymphocytes, and was allospecific. Cell injury manifest by 51Cr release was calcium dependent and was inhibited by pretreatment of lymphocytes with phorbol ester to deplete protein kinase C. Myocyte injury was also prevented by pretreatment of sensitized lymphocytes with anti-Thy 1.2 or anti-CD8 antibody plus complement but not by treatment with anti-CD4 antibody, indicating that CD8+ cytotoxic T cells are involved. Altered myocyte contractile motion preceded myocyte lysis (51Cr release), was characterized by an initial reversible decrease in amplitude of contraction, and was followed by rapid and irregular beating with eventual complete cessation of contraction. Contractile alterations induced by sensitized lymphocytes were inhibited by elimination of CD8+ cells.

Myocyte injury can be produced by sensitized cytotoxic T lymphocytes in vitro and is calcium and protein kinase C dependent. The contractile abnormalities produced appear to be similar to those observed in cardiac transplant patients undergoing rejection, and thus this model system promises to allow investigation of the mechanisms involved.