Modulation of immunity by soluble mediators

Immunosuppressive lymphocyte factors: characterization of the IDS-producing cell in the experimental model of antigenic competition

Inhibitor of DNA synthesis, is a soluble, protein lymphocyte factor which nonspecifically suppresses in vitro lymphocyte responses to antigens or mitogens. It is secreted in large amounts in vivo in some experimentally induced immunological paralysis. Here, we have defined the cell secreting IDS in one experimental model of non-specific immune-suppression, ie., that of antigenic competition. Lymphocytes of rats injected with a large dose of ovalbumin intravenously, show no immunologic response to the same or other antigens or mitogens 24 hr later. At this time, spleen cells of these rats secrete large amounts of the inhibitor into culture supernatants. However spleen cell supernatants of T-depleted rats do not contain the activity. Further, maximal inhibitor concentrations are obtained in the first 2 days of culture when more than 65% of cultured cells are large blasts actively synthesizing protein. As the number of actively metabolizing blast cells decrease in subsequent days of culture inhibitor concentration falls. Finally thymocytes of rats pretreated with hydrocortisone acetate, to deplete thymus cortex cells are unable to secrete inhibitor in culture. These findings reveal that the cells producing inhibitory DNA synthesis in an animal made tolerant with a supra-optimal dose of antigen is an active blast transformed T cell (present in the spleen and thymus). In the thymus the cell making inhibitor appears to reside in the thymus cortex. Previous experiments have confirmed that an identical cell causes nonspecific immune-suppression in vitro. We suggest that this cell produces in vivo tolerance in antigenic competition through the release of inhibitor to DNA synthesis.