The Expression of Tumor Rejection Antigen on Rat Fetus Fibroblasts Transformed by the ras Oncogene

The expression of tumor rejection antigens (TRA) was analyzed on clones of rat fetus‐derived fibroblasts, WFB, transformed or transfected by oncogenes. It was shown that a tumorigenic W14 clone, which is an activated H‐ras transformant of parental WFB, expressed TRA in transplantation experiments using syngeneic WKA rats. The data also showed that W14 TRA was acquired in the event of cell transformation, since it was not detected on parental non‐transformed WFB cells or Wmyc‐4 clone which is a transfectant of WFB by mouse plasmacytoma‐derived c‐myc DNA. However, TRA was not expressed or at least was not detected on highly tumorigenic W31, another clone of H‐ras transformants of parental WFB, in the transplantation experiments. We also assessed the level of expression of major histocompatibility antigens (MHC) class I molecules on these cells by using R4‐8B1 Mab that reacts specifically with rat class I antigen. The data indicated that it was decreased on W14, W31, and Wmyc‐4, but not on parental WFB. Although this molecule was weakly positive on W14 cells, W31 and Wmyc‐4 showed even greater decreases. These data may indicate that the TRA expression and its recognition by syngeneic hosts are dependent upon the transformed clones, although their parental cell is the same. We discuss in detail this difference of expression and recognition of TRA in the context of the cell transforming process.