FUNCTIONAL COMPARISON OF THE INDUCTIONS OF NADPH OXIDASE ACTIVITY AND FC-GAMMA-RI IN IFN-GAMMA-TREATED U937 CELLS

The capacity to generate Superoxide anion (O-2) can be induced in U937 cells by various agents known to cause myeloid cell differentiation. Other reported differentiation events include diminished cell proliferation and the induction by gamma-interferon (IFNγ) of Fc receptors for immunoglobulin G1 (FcγRI). In this study, we differentiated U937 cells and high FeγRI-expression mutants of U937 cells by treating them with IFNγ. We compared the time courses over which surface FcγRI became maximal, NADPH oxidase activity was induced, and the antiproliferative effect of IFNγ was detected. Oxidase activity was measured by stimulating cells with PMA or by activating surface FcγRI using aggregated human IgG1 or second antibody crosslinking of mAb 32/Fcγ RI complexes. We found that IFNγ in the absence of additional lymphokines induced high levels of oxidase activity in maximally differentiated U937 cells with even higher levels in the fully differentiated high-Feγ RI expression mutants (>8 nmoles/106cells/min for A12.13 cells). Over the course of differentiation, maximal induced levels of Fcγ RI were reached after 1 to 2 days of IFNγ treatment, prior to the antiproliferative effect of the lymphokine. In contrast, oxidase activity was induced after a lag of approximately 2 days, becoming maximal only after 4 to 6 days of IFNγ treatment. This comparison of the induction of FcγRI with that of oxidase activity triggered through Fcγ RI indicated that the rapid increase of surface receptor was not accompanied by a completion of the pathway of Feγ RI-mediated oxidase activity. However, the time courses of induction detected by PMA and Feγ RI-agonists were coincident suggesting that the development of oxidative capacity could be due to the induction of components required by both the PMA- and surface receptor-mediated pathways. There are several oxidase components that are known to be IFNγ-inducible, such as the oxidase flavoprotein, a b558 cytochrome peptide, and oxidase-requiring cytosolic components, and it is possible that one or a set of these components could be the limiting factor(s) for IFNγ-induced oxidase activity. © 1990.