Markers of macrophage heterogeneity: Altered frequency of macrophage subpopulations after various pathologic stimuli

Among the various populations of splenic macrophages from normal mice, there were small subpopulations which ingested sheep erythrocytes coated with IgM (EIgM) and uncoated sheep erythrocytes (E). The cells which were best able to ingest these particles also had the capacity to cluster into foci after 24 hr of incubation on glass coverslips. The number of macrophages ingesting these particles increased dramatically in the spleens of malaria-infected mice. Among the normal resident peritoneal macrophages, there was a small subpopulation which ingested sheep erythrocytes coated with IgM and complement (EIgMC), but there were very few cells which ingested EIgM or E. Only a transient increase in the percentage of cells able to ingest EIgMC was detected among the peritoneal macrophages from malaria-infected mice. However, in mice bearing the ascitic thymic lymphoma RL♂l, a large increase in the percentage of peritoneal macrophages capable of ingesting EIgMC was observed when the ascites fluid had just begun to accumulate, and, as the tumor load increased, peritoneal macrophages obtained from the ascites fluid ingested E and EIgM as well as EIgMC. Thus, various pathologic stimuli led to an alteration in the frequency at which various macrophage subpopulations were encountered. Because macrophages capable of ingesting E and EIgM were found in quite low frequency in normal mice, documentation of conditions in which enhanced numbers of these cells appeared provided an experimental system which facilitated the study and characterization of these cells and their receptors.