LOSS OF HLA HEAVY-CHAIN AND BETA-2-MICROGLOBULIN IN HLA NEGATIVE TUMORS

Expression of HLA class I antigens on the cell surface requires the association of heavy chain, endogenous peptide and beta-2-microglobulin (beta-2m). We have studied the expression of free class I heavy chain and beta-2m in cryostatic sections of 51 HLA class I negative human tumours of different origin. Selective low expression of beta-2M was observed only on the 9 colorectal adenocarcinomas. In contrast, simultaneous under-expression of heavy chain and beta-2m was detected in the rest of the tumours studied. Our results suggest that the accumulation in the cytoplasm of HLA heavy chain in HLA negative colorectal carcinomas is a particular mechanism that cannot be applied to all HLA negative tumours.