"Ia-like" antigens on human T cells.

Human T lymphocytes have been tested for cell surface p. 28,33 "Ia-like" heteroantigen and DRw alloantigens. Small numbers (1--5%) of sheep (E) rosette or T antigen-positive, surface immunoglobulin-negative (E+, T+, smIg-) T cells were Ia+; these cells appeared to be restricted to the TG subset. Following activation by allogeneic lymphocytes or sperm, or by purified protein derivative of tuberculin (PPD), the proportion of positive T cells increased substantially. DRw typing indicated that Ia specificities on activated T cells were not acquired passively from the stimulator cells, suggesting therefore that either "selection" of a small DRw+ cell subset or derepression and/or exposure of DR locus gene products occurs during T cell activation.