Macrophage T cell interaction. Induction in vitro of a mediator with potent antisuppressor activity

A simple in vitro method is described for the induction of a potent mediator that interferes with suppressor cell function. The mediator consists of three easily identifiable components, Ig, class II determinants and antigen, that form a unique complex similar to, or identical with, the complexes detected in vivo within 3-6 h after immunization. The formation of the antisuppressor mediator in vitro takes place in two steps: the first involves a macrophage-T cell interaction which generates an 'intermediate complex' containing antigen and class II determinants. In the second step the addition of immunochemically purified IgG from normal mouse serum to the macrophage-T cell supernate generates potent antisuppressor activity, which is assayed by the conversion of suppression to immunity. It is suggested that the IgG interacts with the 'intermediate complex' giving rise to the final complex identical to that found in vivo 6 h after immunization. No activity is detected when IgG is added to a supernate of antigen-fed macrophages in the absence of T cells. Furthermore, the T cell plays an additional important role in the formation of the final complexes since it restricts the source of the IgG that will generate the antisuppressor activity. In other words the antisuppressor function is detected only if the IgG matches the donor of the T cell in the Igh locus. The T cell involved in the formation of the complex is the Ly1+ subpopulation. This method should allow elucidation of the genetic, cellular and molecular mechanisms in the activation of this important T cell pathway.