Membrane associated antigens of human malignant melanoma. III. Specificity of human sera reacting with cultured melanoma cells.

Sera from melanoma patients, healthy donors, pregnant women and patients with types of tumors other than melanoma were tested on various melanoma lines as well as on a cultured brain tumor and adult skin fibroblasts, using a microimmune adherence test. Positive reactions against all cell lines were found in serum from each group of donors. The degree of reactivity was dependent on the cell line used. Sequential absorption with AB Rh+ and pooled platelets of more than 200 donors either reduced the titer of sera or rendered a great part of the sera negative, demonstrating that antibodies against HL-A antigens and other tissue antigens were involved. The remaining positive sera were further absorbed with pooled cells from 6- to 8-week-old fetuses. This step abolished the reactivity of most sera, indicating the relatively high frequency of antibodies in males and females against fetal antigens expressed also on melanoma and other cells. In order to determine the specificity of the few remaining positive sera, absorptions with three different melanoma cell lines, a brain tumor and fibroblasts were carried out. The results showed only partial cross-reactivity between different cell lines. No evidence was obtained from this study for the existence of a common cross-reacting membrane-associated antigen on human malignant melanoma. Antigens that could be readily detected seemed mostly to be tumor-associated fetal antigens.