Suppression of hepatic allograft rejection in the rat by mitomycin C-treated donor splenocytes: in situ splenic distribution of donor class I major histocompatibility complex antigen-positive cells in the recipient.

A single intravenous injection of 3 x 10(6) donor splenocytes treated with mitomycin C (MMC) 7 days before hepatic transplantation prolongs survival of hepatic allografts in the ACI(RT1a) to LEW(RT1(1)) rat combination. This effect is donor specific. The in situ distribution in the recipient of the donor cells administered preoperatively was investigated using intracellularly fluorescence-labeled donor splenocytes. The donor cells were accumulated mainly in the splenic white pulp and lymph nodes at 12 and 24 hr after injection. Contrarily, very few cells were seen in the thymus, liver, kidney, and lung. The number of cells with dull and weak fluorescence began to increase in the splenic white pulp and lymph nodes at 24 hr after injection. This may indicate the breakdown of donor cells by recipient cells. In contrast, a number of donor cells could be detected even after 48 hr and a few cells at 7 days after splenocyte injection in the LEW-to-LEW isogeneic combination. As we previously revealed the role of class I major histocompatibility complex (MHC) antigens in prolonging hepatic allograft survival in the rat, the splenic distribution of donor class I MHC-positive cells in the recipient after intravenous administration of MMC-treated donor splenocytes was studied using immunostaining with a MN4-91-6 mouse anti-rat RT1.Aa class I MHC monoclonal antibody. The donor class I-positive cells accumulated mainly in the splenic white pulp at 12 and 24 hr after injection. This is similar to that observed in the fluorescence study. Within 48 hr after injection, most cells had disappeared from the recipient tissue. These findings suggest that the splenic white pulp, a T-dependent area, may play an important role in inducing immunological unresponsiveness.