Mls and the helper T-cell repertoire. I. Mls as a regulator of T-helper cell activation.

We provide evidence that the Mls reaction involves a broad cross-section of the helper cell population. In addition to those cells reacting overtly to Mls stimulatory spleen cells, there is a second large population of helper cells that are affected by an Mls difference. This latent Mls effect is manifested by either synergy or antagonism in mitogen-mediated, Ia-dependent T-cell activation, depending on Mlsa or Mlsb phenotypes of stimulator cells, respectively. Our data can be explained by attributing to Mls alleles the function of differential regulation of autoreactivity of T cells. The results show that the concept of the Mls exerting a negative signal deserves serious consideration.