T cell responses to alloantigens. I. Studies of in vivo and in vitro immunologic memory and suppression by limit dilution analysis.

A limit dilution technique was used to study the frequency of cytotoxic T cell precursors (f pre Tc) in the peripheral blood lymphocytes (pbl) of naive and alloimunized mice. It was found that alloimmune mice showed a 2- to 5-fold specific increase in the f pre Tc reactive to the immunizing alloantigens. This technique was further adapted for use as a sensitive in vitro assay for alloantigen-specific suppressor T cells. It was found that nonimmunosuppressed B6AF1 mice bearing surviving B10.BR cardiac allografts had circulating alloantigen-specific suppressor cells. In vitro it was shown that the culture of heat-inactivated B10.D2 spleen cells with B6AF1 spleen cells gave rise to alloantigen-specific B6AF1 suppressor cells.