Many observations have led to a general hypothesis in which T cells that mediate helper functions have the Ly phenotype 1+,2- and are specific for I region determinants whereas T cells which mediate suppressor functions are Ly1+ or -,2+ and preferentially recognize K or D determinants. However, there are some exceptions to this dichotomy. We have shown that allogeneic helper effects can be generated to K and D determinants and suppression can result from I region differences. These exceptions raise the question of which factor determines the Ly phenotype of the T cell—the function of the cell or the MHC determinant that is recognized by the cell. In the experiments to be presented, we show that those helper T cells stimulated by K, D differences are Ly2+, while those stimulated by I region differences are Ly2-.

Positive allogeneic effects were determined by titrating mitomycin-treated, nylon wool passed splenic T cells into allogeneic B cells (anti-T treated spleen) plus SRBC.

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