SUPPRESSED ALLOREACTIVITY AND MIXED CHIMERISM IN RATS WITH ACCEPTED CARDIAC ALLOGRAFTS BY INTRATHYMIC INJECTION OF DONOR BONE-MARROW CELLS

Intrathymic injection of donor bone marrow cells (ITBMCs) at the time of transplantation and treatment with antilymphocyte serum (ALS) permi tted the indefinite survival of Brown Norway (BN, RT1(n)) rat heart gr afts in 6 out of 8 Lewis (LEW, RT1(1)) rat recipients. LEW recipients with long-surviving BN heart grafts (LSGs) also accepted additional BN heart grafts without further immunosuppression, though they rejected Piebald Virol Glare (PVG, RT1(c)) rat heart grafts in the usual fashio n. In the in vitro study, the proliferative response of the lymphocyte s from LEW recipients with LSGs remained suppressed when they were sti mulated by BN spleen cells, but not when stimulated by PVG cells. Bone marrow cells (BMCs) from LEW rats with LSGs showed strong, nonspecifi c, suppressive effects on the proliferative response in the mixed lymp hocyte culture reaction, suggesting that one of the possible explanati ons for tolerance might be the involvement of a suppressor mechanism.