Abstract
We have previously shown that the methyl‐cholanthrene‐induced BALB/c fibrosarcoma C‐1 syngeneically transplanted in vivo expressed, in addition to its original H‐2^d^ and tumor‐associated transplantation antigens, also the foreign H‐2K^k^ 23, 1, 5, 11, 25 specificities. In the present study we have investigated the expression and the immunogenicity of these antigens on an in vitro line of C‐1 tumor. The binding of C57BL/6J or C3Hf anti‐BALB/c sera or that of monospecific alloantisera to H‐2^d^ specificities on plated C‐1 cells (evaluated by the indirect isotopic ^125^I‐antiglobulin assay) showed that the expression of H‐2^d^ antigens was very low or undetectable on the tumor kept in vitro. Absorption by the in vivo and in vitro maintained C‐1 cells of the complement‐dependent cytotoxicity on BALB/c normal lymphoid cells of the C75BL/6J anti‐BALB/c serum confirmed the lower expression of H‐2^d^ antigens on C‐1 kept in vitro as compared to the in vivo transplanted tumor. The H‐2^k^ antigens found on C‐1 were also examined by the above methods using BALB/c anti‐C3Hf, anti‐AKR, anti‐C57BL/6J polyspecific sera and also monospecific alloantisera directed to H‐2^k^ antigens. The C‐1 cultured cells displayed a significant reduction of H‐2^k^ antigens as compared to the in vivo C‐1 tumor, the antigen 5 being undetectable on the in vitro cells. Allogeneic and syngeneic sera raised against in vitro or in vivo C‐1 cells were tested on either BALB/c or C3Hf normal lymph‐node cells by the complement‐dependent cytotoxicity assay. A significantly higher titer of cytotoxic antibodies to H‐2^d^ and to H‐2^k^ was obtained in the allogeneic and syngeneic sera respectively, after immunization with the in vivo C‐1 cells as compared to sera raised against the in vitro tumor line. Transplantation studies showed that both in vitro and in vivo C‐1 lines possess the same tumor‐associated transplantation antigen whose expression was non‐significantly reduced on the cultured cells.