In situ subpopulations of lymphocytes in human colorectal carcinomas

Subpopulations tumour-infiltrating lymphocytes were studied in 13 patients with colorectal carcinoma using cryostat immunohistochemistry. Murine monoclonal antibodies (MAB) to the surface phenotype of lymphocyte subpopulation were used in an indirect immunoperoxidase method to demonstrate T (MAB OKT3), T helper (MAB OKT4), T suppressor (MAB OKT8) and B lymphocytes (MAB B1). Langerhans cells were demonstrated using MAB OKT6. All cells reacting with each monoclonal antibody were more prevalent in the stroma of the tumour than within the sheets of malignant cells. In both these areas, OKT8-positive cells were significantly more numerous than OKT4-positive cells, as estimated quantitatively by point counting on a fixed grid. In uninvolved areas of normal mucosa, OKT4-positive lymphocytes were in the majority. OKT6-positive cells were present in large numbers within tumour cells and in close association with lymphoid aggregates. The presence of large numbers of OKT8-positive cells in situ in human colorectal carcinomas may be a cellular mechanism in favour of tumour growth. OKT6-positive cells in situ suggest that mechanisms for antigen processing and presentation are well represented in human colorectal carcinomas.