THE COMPLEMENT REGULATORY PROTEINS CD46 AND CD59, BUT NOT CD55, ARE HIGHLY EXPRESSED BY GLANDULAR EPITHELIUM OF HUMAN BREAST AND COLORECTALTUMOR-TISSUES

Three of the proteins protecting cells from autologous lysis by comple ment are: membrane cofactor protein (MCP; CD46), an inhibitor of the m embrane attack complex formation (CD59), and decay accelerating factor (DAF; CD55). We have investigated the expression of these proteins in breast and colorectal carcinoma by immunohistochemistry and immunoblo tting of breast tissue for CD46. CD46 was consistently and strongly ex pressed in the epithelial compartment in 26/28 ductal carcinomas of th e breast, 9/9 fibroadenomas, and 9/11 cases of control non-neoplastic breast tissue. CD59 showed a similar degree of expression in the fibro adenomas (9/9), but was less strongly expressed in carcinomatous (22/2 8) and control (5/11) tissues. In marked contrast, no CD55 expression was detected in tissue from 15 ductal carcinomas. Immunoblotting of br east tissue for CD46 showed the same size of the molecule as for lymph ocytes. It had however considerably stronger expression in tumour tiss ue than in non-neoplastic tissue. CD46 and CD59 were either lacking or only weakly expressed in the epithelial component of control colorect al mucosa: 2/15 and 5/15, respectively. In contrast, tissue samples fr om colorectal adenocarcinomas showed clear staining for both CD59 (10/ 18) and, more markedly, CD46 (15/18). There was no association between the pattern or intensity of CD46 and CD59 expression and tumour diffe rentiation. As the complement regulatory proteins CD46 and CD59 are al so strongly expressed by trophoblast at the fete-maternal tissue inter face, these results support the concept that similar mechanisms are em ployed both by the genetically dissimilar fetus and certain tumours to evade immune attack by their host.