title: Enhancement of macrophage immune and nonimmune receptor-mediated phagocytosis by a low molecular weight soluble factor from resident thymocytes.
abstract: Macrophage phagocytic activity is regulated in part by products of activated T lymphocytes. We previously reported that a heat-stable soluble factor derived from resident (nonactivated) thymocytes increases murine peritoneal macrophage Fc-dependent phagocytosis. In the present study, we further investigate the effect of the thymocyte factor on immune and nonimmune receptor-mediated phagocytosis, Fc receptor expression, and its approximate m.w. After 4 days of incubation, cellfree thymocyte supernatant produced a mean (three experiments) 2.10-, 2.08-, and 1.97-fold increase in macrophage phagocytosis of C3-, IgG-, and tannic acid-treated erythrocytes, respectively. Macrophage IL 1 production was not enhanced by a similar concentration of thymocyte supernatant. The thymocyte factor(s) increased the number of IgG2a Fc receptors (FcRI) from 2.4 x 10(5) to 3.8 x 10(5) receptor sites per macrophage. The number of Fc receptors that bind IgG1 and IgG2b (FcRII) was not altered. The soluble factor(s) that increased Fc-mediated phagocytosis passed through both 6000- to 8000-dalton and 2000-dalton cutoff dialysis membranes and eluted from a Sephadex G-25 Fine column over a m.w. range of 200 to 1000 daltons, with a peak activity at 450 daltons. These data suggest that resident thymocytes enhance macrophage phagocytosis of opsonized and nonopsonized particles through the elaboration of a low m.w. substance(s).
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology; D005260:Female; D007375:Interleukin-1 / Q000096:biosynthesis; D008213:Lymphocyte Activation; D008222:Lymphokines / Q000502:physiology*; D016215:Macrophage-Activating Factors; D008264:Macrophages / Q000276:immunology* / Q000378:metabolism / Q000502:physiology; D051379:Mice; D008806:Mice, Inbred AKR; D008807:Mice, Inbred BALB C; D008809:Mice, Inbred C3H; D008970:Molecular Weight; D010587:Phagocytosis; D011961:Receptors, Fc / Q000276:immunology / Q000378:metabolism / Q000502:physiology*; D013601:T-Lymphocytes / Q000276:immunology / Q000378:metabolism*
chemical_list: D000911:Antibodies, Monoclonal; D007375:Interleukin-1; D008222:Lymphokines; D016215:Macrophage-Activating Factors; D011961:Receptors, Fc