Enhanced in vitro immunogenicity of H-2 antigens in the presence of la antigens.

In a primary and secondary MLC the in vitro immunogenicity of allogeneic PHA induced blast cells (which lack i region coded determinants) was compared to that of LPS imduced blast cells. Unlike LPS induced blast lymphocytes (stimulator cells) which induced high cytotoxic activity, PHA induced blast cells were found to be poor stimulator cells in a primary MLC. Yet in a secondary MLC both types of stimulator cells induced cytotoxic activity equally well. Using one type of responder cells the relative immunogenicity of various stimulator cells incompatible on either the H-2K and H-2D region or on the i region, or on the complete H-2 complex, was compared. The magnitude of cytotoxic response induced in a strain combination differing at the complete H-2 complex exceeded by far the sum of separate responses obtained against the H-2D region, H-2K region and the i region coded determinants respectively. These results suggest that the presence of i region coded determinants on allogeneic stimulator cells enhance the in vitro immunogenicity of H-2K and H-2D region coded transplanatation antigens.