Immunohistologic analysis of the T-cell and macrophage infiltrate in 1,2-dimethylhydrazine-induced colon tumors in the rat.

The infiltrating mononuclear cell (MNC) type, and the localization of major histocompatability class I and class II antigens within 1,2-dimethylhydrazine (CAS: 540-73-8)-induced colonic tumors and normal colonic mucosa in WF/Hsd BR rats were investigated by immunoperoxidase staining of frozen sections with the use of monoclonal antibodies. Infiltrating T-cells stained with monoclonal antibodies W3/13, W3/25, and MRC OX 8; W3/13+ cells were predominant. The most numerous and consistently observed infiltrating cell type was an la antigen-bearing (MRC OX 6+, MRC OX 17+) macrophage. A smaller subpopulation of macrophages, staining with W3/25, showed a similar distribution within tumors. In adenomas and in some well-differentiated adenocarcinomas, the infiltrating MNC were concentrated at the tumor periphery and were in close proximity to neoplastic epithelia, but without evidence of consequent tumor cell necrosis. In all other tumors, infiltrating host cells were confined to the connective tissue stroma dividing clusters of neoplastic glands. The extent of cellular infiltration and the phenotypes of infiltrating cells did not correlate with the degree of tumor differentiation or with tumor size. Expression of MHC class I antigens (MRC OX 18) by tumor cells did not differ from that of normal epithelia, and neoplastic epithelia were uniformly negative for class II antigens (MRC OX 6, MRC OX 17). The data do not support a role for cytotoxic macrophages or T-cells in the local response to colon tumors.