Phagocytes in cell suspensions of human colon mucosa

Because little is known of the phagocytes of the human colon we enumerated these cells in mucosal suspensions and studied their phagocytic activity. Phagocyte rich suspensions were made by EDTA collagenase dissociation followed by elutriation centrifugation. Phagocytosis was evaluated by measuring cellular radioactivity after incubation of phagocytes with 3H-adenine labelled E coli ON2 and checked microscopically. Dissociation of normal mucosa from colorectal neoplasms yielded means of 1.9 X 10(6) eosinophils, 1.4 X 10(6) macrophages and 2 X 10(5) neutrophils per gram of mucosa. Visually normal mucosa of inflammatory states yielded 2.2 X 10(6) eosinophils, 2.3 X 10(6) macrophages and 7 X 10(5) neutrophils per gram of mucosa. Phagocyte rich suspensions of normal mucosa from tumour patients phagocytosed 21.8% of a pool of opsonised tritiated E coli ON2 and by microscopy 100% of mucosal neutrophils ingested bacteria, 83% of eosinophils were phagocytic, and 53% of macrophages contained bacteria. These results suggest that in the human colonic mucosa, the eosinophil is more abundant than the macrophage and the per cent of those cells exhibiting phagocytosis is intermediate between that of the macrophage and the neutrophil. Thus these three types of cells are actively phagocytic and share the potential for a major role in host defence against invasive enteric bacteria.