Changes in distribution of human malignant melanoma membrane antigens in the presence of human antibody by immunofluorescence.

Four viable human melanoma cell lines demonstrated full-surface fluorescence (FSF) after incubation at room temperature with antisera from three melanoma patients receiving autologous or homologous immunization with irradiated cultured melanoma cells and Bacillus Calmette-Guérin. By sequential immuno-fluorescent staining, it had been shown that FSF was followed by capping and extrusion of antigen-antibody complexes. One melanoma cell line was tested against its autologous antiserum. In the presence of excess antigen, FSF cells peaked to 25% of the total cell population at 30 min. Maximum capping (20%) was noted at 3 hr. When excess antibody was present, FSF cells were 30% at 2 min and capped cells peaked to 25% at 1.5 hr. Capping ceased at 4 degrees under both conditions. When the serum-treated cells were reincubated after fixation with methanol, 80 to 85% of the cells showed FSF at 2 min to 13.5 hr. Negative controls were preimmune sera and skin fibroblasts. These experimental data suggest the presence of embedded and protruding melanoma membrane antigens in the phospholipid layer. Methanol amy dissolve the lipid layer and expose the embedded antigens. The extrusion of melanoma antigen-human antibody complexes in vitro seems to be a possible mechanism of antigen shedding by melanoma cells in vivo.