Cross-reactivity of murine anti-human high molecular weight-melanoma associated antigen monoclonal antibodies with guinea pig melanoma cells.

To identify melanoma associated antigens (MAAs) shared by human and guinea pig melanoma cells, a battery of murine monoclonal antibodies (MoAbs) to human MAA and an antiserum to S100 protein were tested with four newly established guinea pig melanoma cell lines. Only the monoclonal antibodies 149.53 and 225.28 which recognize distinct determinants of the human high molecular weight-MAA (HMW-MAA) reacted with all four guinea pig melanoma cell lines. To compare the binding site of MoAbs 149.53 and 225.28 with guinea pig and human melanoma cells, inhibition binding experiments were performed with antiidiotypic monoclonal antibodies which completely inhibit the binding of MoAbs 149.53 and 225.28 to human melanoma cells. The binding of MoAb 149.53 to guinea pig melanoma cells was partially inhibited by antiidiotypic MoAbs MF9-10 and MK1-180 which recognize distinct private idiotopes within the antigen combining site of MoAb 149.53. On the other hand the binding of MoAb 225.28 to guinea pig melanoma cells was completely inhibited by antiidiotypic MoAbs MF11-30 and TK1-F2 which recognize distinct private idiotopes within the antigen combining site of MoAb 225.28. These results suggest that the determinant recognized by MoAb 149.53 on guinea pig melanoma cells is similar but not identical to that recognized on human melanoma cells, while the determinants recognized by MoAb 225.28 on the two types of cells do not display any detectable differences under the experimental conditions tested. The target structure on the guinea pig melanoma cells identified by MoAbs 149.53 and 225.28 is a Mr 280,000 molecule which has the same apparent molecular weight as one of the two subunits of the HMW-MAA synthesized by human melanoma cells. Sequential immunoprecipitation experiments with guinea pig melanoma cells showed that the determinant recognized by MoAb 149.53 is expressed on a subpopulation of the molecules recognized by MoAb 225.28. Immunohistochemical staining with MoAb 225.28 of a variety of different tissues from normal adult guinea pigs showed that the corresponding antigenic determinant is detectable only in basal cells of epidermis and hair follicles of skin. S100 protein, which is a cytoplasmic constituent of normal human melanocytes, benign nevi, and malignant melanocytes, was also detected in the cytoplasm of the four cultured guinea pig melanoma cells lines. The results of the present investigation may lead to a better understanding of the phylogenetic evolution of the human HMW-MAA and suggest that guinea pig melanoma may serve as a useful animal model for immunobiological studies and carcinogen-induced tumorigenesis investigations.