Immunoregulatory circuits among T-cell sets. I. T-helper cells induce other T-cell sets to exert feedback inhibition.

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Abstract
The hypothesis was tested that cells carrying the Ly1+Ly23- surface phenotype are programmed exclusively for helper and not suppressive activity regardless of external conditions such as the mode or type of antigen stimulation. Purified populations of [mouse] Ly1 cells were stimulated with antigen in vitro using conditions devised to induce unselected T [[thymus derived] cells to express optimal levels of antigen specific T-suppressor activity. After such stimulation, Ly1 cells generate SRBC[sheep red blood cell]-specific T-helper activity but not T-suppressive activity. The Ly1.2+,2.2/3.2- surface phenotype is a stable, and probably invariant, marker of T cells that are programmed to express only helper activity and have lost the capacity to directly suppress the antibody response. The genetic program for a single differentiated set of cells probably combines information for cell surface phenotype and function. Antigen-stimulated Ly1 cells, in addition to inducing B [bone marrow derived] cells to secrete antibody, can induce or activate other sets of resting T cells to develop profound suppressive effects. The surface phenotype of this feedback suppressive T-cell set is Ly1+2+3+Qa1+. Activation of resting Ly123 cells by immune Ly1 TH cells may represent an important homeostatic immunoregulatory mechanism.

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