Inappropriate alloantigen-like specificities detected on reticulum cell sarcomas of SJL/J mice: characterization and biologic role.

SJL/J (H-2s) reticulum cell sarcomas (RCS) of different origins (spontaneous, transplantable, and cell lines) carry antigens that cross-react with BALB/c (H-2d) and C57BL/6 (H-2b) alloantigens in tests measuring cell-mediated cytotoxicity, antibody-dependent cytotoxicity, and immunofluorescence. These inappropriate antigens on RCS cells were not detected on normal SJL/J splenocytes. Immunochemical analysis of the inappropriate antigens by two-dimensional gel electrophoresis was performed with SJL/J anti-BALB/c and monospecific anti-H-2Dd sera. These sera precipitated 45,000 molecular weight molecules from BALB/c lymph node cells and from SJL/J in vivo and in vitro RCS tumor that appeared very similar. The sera also precipitated molecules from SJL/J lymph node cells that resemble the BALB/c and RCS molecules. Because of the highly immunogenic nature of RCS in vivo, we examined antigen-reactive cell opsonization (ARCO) as a possible mechanism of tumor enhancement. 125IUdR-labeled SJL/J anti-RCS lymphocyte (*ARC) were diverted to the liver (opsonized) when injected i.v. into syngeneic tumor-bearing mice. Furthermore, SJL/J anti-BALB/c *ARC were opsonized in mice with BALB/c positive spontaneous tumors but not in mice with H-2d negative tumors. Our results show that RCS tumors express inappropriate alloantigens (cryptic on normal cells) that are immunogenic in vivo. Specific antitumor ARC are opsonized in tumor bearers provoking ineffective immunity and survival of antigenic spontaneous RCS tumors.