Modulation of Fc-mediated phagocytosis by cyclic AMP and insulin in a macrophage-like cell line
Immunoglobulin Fc Fragments
Studies on genetically selected mutants in phagocytosis of E[IgG] indicated that the defect in some mutants could be corrected by addition of 8 Br-cAMP, and suggested that cyclic AMP may be involved in the mechanism of phagocytosis through the Fc receptor. In order to elucidate the role of cyclic AMP in phagocytosis in the parental, nonmutant macrophage-like cell line, J774.2, it was necessary to employ restrictive conditions which rendered phagocytosis suboptimal. When 4774.2 cells were cultured in nontissue culture Petri dishes phagocytosis was markedly reduced. Addition of 8 Br-cAMP or inducers of intracellular cyclic AMP such as isoproterenol restored the phagocytic ability of these cells. Similarly, treatment of the parental J774.2 cells with insulin reduced the level of phagocytosis, and once again this suppression could be corrected by addition of 8 Br-cAMP. In no case did AMP mimic the effects of 8 Br-cAMP. The effect of cyclic AMP action in this system was not instantaneous, but rather reached optimal levels at 5 to 10 hr, suggesting that cyclic AMP is not the immediate signal for phagocytosis. The genetic analysis of macrophage variants may provide a useful model for studies on the mechanisms of phagocytosis, and also the effects of insulin and cyclic AMP on an easily measurable biologic function in a specialized cell type.