Clones of helper T cells mediate antigen-specific, H-2-restricted DTH.

It is now well established that in the mouse, helper T cells and killer T cells are two distinct thymus-derived lymphocyte subpopulations, differing from each other in Lyt phenotype and H-2 restriction, among other parameters. Helper T cells are Lyt-1+ and their action in immune responses involves restriction at the H-2I region of the major histocompatibility complex (MHC). Killer cells, on the other hand, are Lyt-23+ and their activity is restricted by H-2K/D (refs 1, 3). In most instances, T cells mediating delayed-type hypersensitivity (DTH) responses share the Lyt phenotype and H-2 restriction of the helper T cell. This raises the question of whether or not helper activity and DTH can be mediated by the same activated T cell. Arguments for both views have been reported. We analysed this question using clones of specific helper T cells, which were obtained by long-term culture in vitro of in vivo primed T cells, followed by single-cell cloning. Here we show that these clones of helper T cells mediate antigen-specific and fully H-2-restricted DTH. The restricting element lies to the left of the I-B region in genetic maps of the mouse MHC.