LOCUS-SPECIFIC ANALYSIS OF HUMAN-LEUKOCYTE ANTIGEN CLASS-I EXPRESSIONIN MELANOMA CELL-LINES

Surface expression of human leukocyte antigen (HLA) class I antigens o n melanoma lines was evaluated by locus-specific monoclonal antibodies (mAbs) with three different techniques: Fluorescence-activated cell s orting (FACS), immunohistochemistry with cytospin preparation (ICP), a nd complement-mediated cytotoxicity (CMC). Eleven HLA class I-expressi ng cell lines developed from metastases were used. Specific expression of HLA loci was examined under routine culture conditions and after 4 8-h incubation in interferon-gamma (IFN-gamma; 500 U/ml). Loss of alle lic expression was seen in one line (586-MEL): Products of genes codin g for HLA-A29 and -B44, in strong linkage disequilibrium, were not det ectable. HLA-A antigens were consistently detected by all methodologie s and minimally affected by pretreatment with IFN-gamma. HLA-B antigen s were detectable in 8 of 11 lines by ICP and 3 of 11 lines by CMC. By FACS the supratypic specificity HLA-Bw6 was expressed at low levels i n most lines (mean fluorescence 47.2 +/- 13.4 and rose to 259.8 +/- 45 .9 after incubation with IFN-gamma; p < 0.001). HLA-Cw antigen detecti on by CMC correlated with HLA-B (p < 0.01), suggesting that down-regul ation and sensitivity to IFN-gamma are shared by the two loci. This lo w expression of the HLA-B antigens may play a role in the evasion of t he host immune response and its up-regulation may be useful in allowin g tumor antigen recognition.