The role of the major histocompatibility complex in the regulation of macrophage-T lymphocyte interaction.

The proliferative response of guinea pig T lymphocytes which have been primed in vivo can only be induced by antigen-pulsed syngeneic macrophages. The development of techniques to prime T lymphocytes in vitro has allowed us to demonstrate that the genetic restriction on the interaction of the macrophage and T lymphocyte is regulated by the Ia antigens of the macrophage used during the initial sensitization step. Following removal of alloreactive cells, T cells can be sensitized to antigen-treated allogeneic macrophages. It thus appears likely that T cells do not recognize antigen per se, but can only be sensitized to antigen-modified membrane components or to complexes of antigen combined with certain membrane molecules. We postulate that the Ia antigens themselves are the products of the immune response genes and function in both macrophages and B lymphocytes as antigen recognition structures.