Mixed leucocyte interaction suppression generated after alloimmunization.

Utilizing a bone marrow cell immunization protocol designed to actively enhance renal or cardiac allografts, the in vitro mixed lymphocyte interaction has been studied. After immunization with allogeneic cells over a wide dose (10(5) to 10(8)) and time range, the mixed lymphocyte interaction using peripheral blood lymphocytes is reduced, and this reduction is shown in mixing experiments to be attributable to a circulating suppressor cell that has adherence characteristics of T lymphocytes. Specificity for in vivo generation of these circulating cells as well as specificity in the in vitro reaction was shown, although a nonspecific suppression background was observed. Allogeneic thymocytes, splenocytes, and platelets were effective in immunizing to generate these cells also. There was no general correlation with the ability to generate these cells and to actively enhance cardiac allografts, since suppression was seen after alloimmunization in strain combination that cannot be actively enhanced.