The spontaneous expression of HLA class-I and class-II molecules in 5 human breast carcinoma cell lines, MCF-7, T47D, ZR75-1, HSL-53, MDA-MB 231, and their modulation during IFN-gamma treatment, are reported. The expression of cell-surface determinants was examined by indirect immunofluorescence using monoclonal antibodies (MAbs) specific for HLA class-I and class-II (DR, DQ and DP) antigens. The biosynthesis and maturation of these molecules were analyzed by 2-dimensional gel electrophoresis analysis (2D-PAGE) of class I, DR alpha, beta and invariant immunoprecipitates. Transcription was analyzed by Northern blot hybridization with HLA class-I and -II cDNA-specific probes. In all cell lines, more than 80% of cells expressed HLA class-I antigens at their surface. 2D-PAGE and mRNA studies showed a variable basal level of HLA class-I biosynthesis and transcription with a constant increase after 1,000 U/ml IFN-gamma treatment. HLA class-II determinants were totally absent from the surface of MCF-7, MDA MB231, ZR75-1 and T47D but they were detected in a small subpopulation of HSL-53 cells (DR 6%, DQ 6%, DP 20%). Spontaneous biosynthesis of HLA-DR molecules in immunoprecipitates analyzed by 2D-PAGE or transcripts in Northern blot were not detected in the 5 cell lines. Treatment with 1000 U/ml IFN-gamma induced or increased the expression of HLA class-II molecules in all cell lines but DQ expression was variable. While T47D, ZR75-1 and HSL-53 increased their transcripts and antigen expression, MDA, MB231 and MCF-7 showed no DQ mRNA transcript. Biochemical analysis of the DR products revealed a classical alpha, beta and invariant (li) chain pattern, but indicated a constant glycosylation defect in the invariant chain in all cell lines, associated with weak expression of the beta chain and the presence of an extra spot of low molecular weight in the acidic part of the gel. Thus, post-transcriptional events did not appear to be totally controlled by IFN-gamma in the different cell lines. These differences in DQ expression and glycosylation process in different breast cancer cells may be important in the activation of the immune response among different individuals.