Elevation of infiltrating mononuclear phagocytes in human colorectal tumors

The distribution of infiltrating monocytes-macrophages and T-lymphocytes in 45 primary colorectal tumors and 8 metastatic lymph nodes has been investigated by immunoperoxidase labeling with monoclonal antibodies (MoAbs). The number of lymphoreticular cells observed in tumor tissue, staged according to Dukes classification, was compared with paired normal tissue and between staged groups by statistical analysis. T-lymphocytes were not significantly elevated above the normal in either Dukes B or C stage tumors, although the IL-2 receptor (MoAb Tac) was expressed by varying numbers of T-cells in both groups. Mononuclear phagocytes increased numerically in both Dukes B (1.5-fold, P-value less than .01) and Dukes C tumors (2.5-fold, P-value less than .001) as compared to those in the uninvolved gut. In addition, the number of both total (MoAbs 3.9, 24) and stimulated mononuclear phagocytes expressing the C3b receptor (MoAb E11) was greater in metastasizing than in nonmetastasizing tumors (P-value less than .01). Thus the T-cell-to-monocyte ratio was altered from 2:1 in normal tissue to 1:1 in advanced tumors. The stromal environment around tumor cells in lymph nodes was similar to that of the primary tumor, but there was a reduction in the proportion of cells expressing the C3b receptor; unlike the primary tumor, there was virtually no infiltration of the tumor epithelium. Although there is a significant alteration in the mononuclear phagocyte population within colorectal tumors, there is no histologic evidence for a cytotoxic role for these cells.