Cell phenotype dependent expression of MHC class I antigens in Burkitt's lymphoma cell lines.

Burkitt's lymphoma (BL) is a highly malignant B cell tumor characterized by three types of chromosomal translocation which constitutively activate the c-myc oncogene by juxtaposing it to Ig coding sequences. Epstein-Barr virus (EBV) infection, hyperendemic malaria and HIV-caused immunosuppression are thought to contribute to the pathogenesis of the tumor. Cell lines derived from EBV carrying and EBV negative BLs often show altered MHC class I antigen expression. The defects include a lower expression of all HLA class I antigens compared to EBV transformed normal B-blasts, and selective down-regulation of certain HLA-A and HLA-C alleles. As a consequence BL cells are often resistant to cytotoxic T lymphocyte (CTL) mediated destruction. Alleles selective down-regulations are found only in cell lines that maintain the tumor cell phenotype while shift towards a more activated 'B-blast like' phenotype is accompanied by HLA class I up-regulation. A similar pattern of HLA class I expression can be found in a subpopulation of germinal center B cells which express a 'BL like' phenotype. Our findings suggest that the HLA class I expression of BL cells reflects the characteristics of the normal B cell precursor and is probably not the result of immune selection.