Reduced immunogenicity of long-term, passively enhanced rat renal allografts and passive transfer of graft protection.

Enhancing alloantiserum was produced by immunizing male BD IX inbred rats with density gradient separated nylon-wool adherent spleen lymphocytes from male rats of the major histocompatibility complex (MHC) different inbred strain Sprague-Dawley (SD). Long-term surviving (BD IX X SD) F1 to BD IX kidney grafts were achieved by treating the recipients with 1 ml alloantiserum at the time of transplantation. After greater than 100 days 7 passively enhanced F1 kidneys were retransplanted into naive BD IX rats. Four out of 7 secondary recipients, producing only low levels of lymphocytotoxic antibodies, survived for greater than 100 days, 3/7 rats died of surgical or infection complications. Twenty-one naive BD IX recipients of normal F1 kidneys were treated with serum (1 ml i.v.) and/or spleen lymphocytes (1 X 10(7) i.v.) obtained from the long-term survivors. An indefinite graft survival was achieved in 13 out of 21 rats. After greater than 150 days 6 out of these 13 passively enhanced F1 kidneys were retransplanted into naive BD IX rats which were challenged at the time of grafting with 4 X 10(7) SD lymphocytes to elicit rejection. Six out of 6 kidneys survived greater than 150 days. Thus, the long-term survival of rat kidney allografts in this model is associated with a strong reduction of graft immunogenicity as well as the development of suppressor cells and enhancing antibodies.