Enumeration of alloreactive helper T lymphocytes which cooperate with cytolytic T lymphocytes

The number of alloreactive helper T lymphocytes (HTL) which cooperate with cytolytic T lymphocytes have been quantified in a sensitive limit dilution system. Approximately 1 in 330 splenic T lymphocytes developed helper activity in response to alloantigen of a single haplotype. Most HTL appeared to cooperate nonspecifically with the cytolytic cells. A significant number of alloreactive HTL precursors recognized H-2 K or D alloantigen, but roughly 6-fold more HTL precursors responded to H-2 I, and roughly 20-fold more responded to non-H-2, presumably Mls, alloantigen. These results support the hypothesis that alloantigen encoded by the H-2 I and non-H-2 Mls regions preferentially stimulate helper T lymphocytes while alloantigens encoded by the H-2 K and D regions preferentially stimulate cytolytic T lymphocytes.