Unconventional lymphocytes involved in rejection of xenogeneic heart grafts.

In this report, the efficacy of cyclosporine A and two monoclonal antibodies, anti-L3T4 and anti-Lyt-2.2, was assessed on first-set rejection of cardiac xenografts. Neither cyclosporine nor anti-Lyt-2.2 monoclonal antibody prolonged the survival of heart xenografts. Anti-L3T4 enhanced acceptance of rat hearts transplanted to C57BL/6 mice 5-fold relative to that observed in control recipients; it did not, however, prolong acceptance of hamster hearts transplanted to mice. Histologic analysis indicated that the cellular infiltrate within rejected hearts was composed of greater than 95% lymphocytes; of these, greater than 99% were Thy-1- and sIg-. These results suggest that rejection of xenogeneic hearts is mediated by unconventional lymphoid cells. This is discussed in the context of whether rejection of allografts and xenografts occur by similar or dissimilar mechanisms.