Hyperthermia-induced shedding and masking of melanoma-associated antigen.

Hyperthermia has been reported to induce a dose-dependent reduction in the expression of melanoma-associated surface antigens. The objective of the present work was to study the mechanisms for the reduction in the expression of the p250 antigen recognized by the monoclonal antibody 9.2.27. Measurements at 37 degrees C showed that antibody binding induced a certain degree of modulation (internalization) of the melanoma-associated antigen. Masking of the antigen due to internalization and/or damage in situ, as well as shedding of the antigen, were measured after hyperthermia, and found to increase in a heat-dose-dependent manner, although for antigen masked this increase was not significant compared with control cells at 37 degrees C. The sum of antigen shed and masked after hyperthermia correlated with the overall reduction in antigen expression measured independently. During hyperthermia, antigen was shed and masked in approximately equal amounts. After the treatment, hyperthermia-induced shedding continued as a function of time and caused a further reduction in antigen expression, but masking did not differ from 37 degrees C controls.