Our main objective is to characterize the immunological properties and molecular nature of inappropriate antigens detected on SJL/J reticulum cell sarcoma (RCS) and to define the role of these antigens in tumorogenesis. We plan to demonstrate the presence of inappropriate alloantigens on spontaneous, transplantable and cultured RCS cells by cell mediated and complement cytotoxicity, and by immunofluorescence. Furthermore, biochemical analysis of inappropriate antigens will be examined by immune precipitation of NP40 lysed 35S methionine labeled tumor cells with specific alloantisera and characterization of the molecules by SDS gel electrophoresis. The role of inappropriate antigens in host stimulation will be investigated by examining the in vivo response to inappropriate alloantigenic specificities in both cellular and antibody mediated assays. The mechanism by which the immune response promotes tumor escape from immune destruction will be investigated including the role of antigen-antibody complexes in specific anti-tumor-antigen-reactive cell opsonization, modulation of tumor associated antigens by circulating antibody, direct tumor mediated suppression of antigen-reactive cells and activation of suppressor cells.