Expression of histocompatibility antigens and characterization of mononuclear cell infiltrates in normal and neoplastic colorectal tissues of humans.

Serial frozen sections were prepared from 22 colorectal carcinomas. Additional samples were obtained from the adjacent normal bowel in 10 patients, from 6 concomitant adenomas in 5 patients, and from another 4 isolated adenomas. Mononuclear cell infiltrates were stained by the indirect immunoperoxidase technique with the use of a panel of 6 mouse monoclonal antibodies to human leukocyte antigens. The degree of infiltration was graded from 4 (heavy) to 0 (nil). The colorectal carcinomas and adjacent normal bowel showed an equal degree of leukocyte infiltration (HLe-1), graded 3-4 in 8 cases and 2-3 in the other 2 cases. In 7 carcinomas cytotoxic-suppressor T-lymphocytes (UCHT-4) graded 2-3 predominated over helper T-cells (OKT-4) graded 0-1. By contrast, in the adjacent normal bowel cytotoxic and helper cells were present in equal numbers. Among the adenomas leukocyte infiltration was grade 4 in 9 and grade 3 in 1. In 9 of the 10 adenomas cytotoxic cells graded 2 predominated over helper cells graded 0-1. The number of helper cells was equivalent among 6 concomitant adenomas and carcinomas from 5 patients. Adenomatous epithelial cells expressed class II major histocompatibility complex antigens (OKIa-1). However, carcinomatous or normal epithelium showed only faint staining with OKIa-1. The similarity in cell infiltration is consistent with an adenoma-carcinoma sequence. The predominance of cytotoxic cells in carcinomas that expressed class I major histocompatibility complex supports the association between lymphocyte infiltration and a favorable prognosis.