associated antigens
Recombinant interferon-y (IFN-y) induced the expression of HLA-DR when added to the culture medium of HLA-DR-melanoma cell lines. In addition, IFN-y induced the expression of another class I1 antigen, HLA-DC, on a HLA-DR' and -DCmelanoma cell line and to a lower level on a -DR-and -DC-melanoma line. IFN-y also enhanced the expression of HLA-ABC and firmicroglobulin, as well as HLA-D R on DR' melanoma cells. In contrast, IFN-a gave no induction of expression of HLA-DR and DC on two DR-melanoma lines, while it did enhance the expression of HLA-ABC and of P2-microglobulin. The expression of 3 out of 6 melanomaassociated differentiation antigens was enhanced by IFN-y treatment. The modulation of antigens by IFN-y was both dose and time dependent. A minimum incubation time of 48 h was necessary for the appearance of HLA-DR on the two HLA-DRmelanoma lines, whereas HLA-ABC and /32-microglobulin were already increased after 24 h. A dose of 20 U/ml IFN-y started to induce the expression of HLA-DR and DC on melanoma cells GLL-19 and Me-43 and a plateau of maximum antigen expression was reached with 100 U/ml. Analyses of IFN-y-treated cells by flow microfluorometry showed a homogeneous distribution of increased staining intensity rather than the appearance of two cell populations. Immunoprecipitation experiments using detergent-solubilized 1251-labeled membrane proteins of IFN-y-treated melanoma cells and a monoclonal anti-HLA-DR antibody confirmed the presence of HLA-DR antigens. When IFN-y-treated cells were cultured without IFN the induced or enhanced expression of HLA antigens was reversible. Eight days after removal of IFN, the HLA-DR level was reduced by more than 90% and the level of HLA-ABC and P2-microglobulin by more than 50%. The demonstration of the ability of HLA-DR-melanoma cells to express HLA-DR after IFN-y treatment was extended to cells from other types of tumor such as gliomas, colon carcinomas and one cervical carcinoma cell line.