Augmentation of macrophage complement receptor function in vitro. II. Characterization of the effects of a unique lymphokine upon the phagocytic capabilities of macrophages.

The means by which a unique lymphokine imparts to macrophages the capacity to ingest complement- (C) coated particles was explored. In contrast to other previously described lymphokines that influence macrophage behavior, the T cell product that enhances macrophage C receptor function was found to act immediately upon contact with macrophages and to be of substantially lower apparent m.w. than either MIF, MAF, lymphotoxin, or interferon. Evidence is presented that indicates that the lymphokine does not act by causing a generalized increase in plasma membrane phagocytic activity or by enhancing phagocytosis mediated by other immunologic receptors. Nor does the lymphokine act by inducing the synthesis of new protein receptors. Our findings suggest that the more likely possibilities by which the lymphokine acts include induction of an increased rate of insertion of C receptors into the macrophage plasma membrane, induction of a rearrangement of C receptors within the macrophage plasma membrane, or a qualitative alteration of the function of existing macrophage C receptors in their relationship with the intracellular machinery involved in phagocytosis.