Heterogeneity of HLA-A,B, Ia-like, and melanoma-associated antigen expression by human melanoma cell lines analyzed with monoclonal antibodies and flow cytometry.

With the use of monoclonal antibodies, indirect immunofluorescence, and flow cytometry, human melanoma cell lines (Colo 38, M-16, and M-21) were examined for the quantitative level of expression of HLA-A,B antigens, Ia-like antigens, and two human melanoma-associated antigens (MAA) referred to as 280K and 94K MAAs. Each of the melanoma cell lines examined showed tremendous heterogeneity with regard to antigen expression. A detailed study of the heterogeneity of the four antigens listed revealed that variation in cell size could, in part, account for the large differences in antigen expression observed. Cell surface density of HLA-A,B antigens, Ia-like antigens, and the 280K and 94K MAAs remained relatively constant over a wide range of cell sizes that were examined, with the exception that small melanoma cells showed a slightly lower mean surface density of MAA expression than did large cells. A novel method was used to detect the expression of the two MAAs as a function of the Colo 38 cell cycle using dual-laser beam flow cytometry. The results of these experiments show that both the 280K MAA and the 94K MAA are differentially expressed during various stages of the cell cycle, with each antigen being maximally detected during G2 + M.