Phagocytic lymphoid cells and transitional cells in the peritoneal cavity

In 71 mice, a study was made of the non-granular phagocytic cells in the peritoneal cavity, both after the intraperitoneal injection of India ink, and by incubation of the non-adherent cells with ink in vitro. Ink was taken up by a number of lymphoid cells, as well as by macrophages and monocytes, referred to jointly as macrophages. In addition, the presence of DNA-synthesizing cells was investigated by radio-autography after incubation of cell suspensions for 1 hour with tritiated thymidine. A small number of labelled macrophages was usually found in the normal peritoneal cavity, and also about 1% of labelled cells with the typical morphological features of the transitional cells seen in bone marrow. During 14 days after the intraperitoneal injection of ink, the combined population of lymphoid cells and macrophages showed an increase in the percentage of lymphoid cells, and a fall in the percentage of macrophages. The phagocytic lymphoid cells did not appear to develop into macrophages. It seems reasonable to assume that the haemopoietic stem cells known to be present in the peritoneal cavity are to be found among the transitional cells, some of which may also be macrophage or lymphocyte precursors.