Differential expression of MHC class II genes in lung tumour cell lines.

Molecular characterization of HLA class II expression was investigated in five lung tumour cell lines at the protein and mRNA levels. The cell lines exhibited a differential expression of HLA-DR, HLA-DP and HLA-DQ products and also showed differences in the inducibility of HLA class II genes by gamma-IFN. Gamma-IFN stimulation induced only HLA-DR expression to varying degrees in three cell lines, while only one cell line showed stimulation for HLA-DP and none for HLA-DQ antigens. These results suggest locus-specific regulation for the three loci. The presence of DR protein on the cell-surface membrane was always positively correlated with the presence of HLA-DR mRNA in the cells. After treatment with 5-azacytidine in the A549 cell line, which expressed the lowest values, there was no effect on HLA class II levels. This suggested that methylation does not play an important role in the lack of MHC class II antigen expression. In addition to studying mRNA levels of HLA class II antigens, we analysed mRNA of the proto-oncogene c-myc and observed a positive correlation of two mRNA: the increments in HLA-DR expression were associated with increments in c-myc expression. This suggests a relationship between the regulatory and HLA-DR antigens control the expression of c-myc and HLA-DR antigens in lung tumour cell lines.