In vitro effects of interleukin-4 on interferon-gamma-induced macrophage activation.

Interferon-gamma (IFN-gamma) and interleukin-4 (IL-4) have been shown to be secreted by distinct T-helper cell subsets which have different roles in the determination of host resistance to infection. We studied the activity of these two cytokines on effector mechanisms of mouse macrophages. In vitro cultured bone marrow-derived macrophages from C57BL/6 mice were treated with IFN-gamma, IL-4, or a combination of both cytokines and the ability to secrete superoxide or nitrite or to restrict growth of Mycobacterium avium and Toxoplasma gondii was then evaluated. We found that IL-4 could inhibit the priming of macrophages for enhanced superoxide production induced by IFN-gamma although IL-4 when used alone did have some enhancing effect of its own. This effect of IL-4 on IFN-gamma-primed superoxide production was dose dependent and could be observed even if the treatment by IL-4 was done 24 hr after treatment by IFN-gamma. IL-4 did not, however, influence the enhanced production of nitrogen reactive intermediates, the induction of bacteriostatic activity against M. avium, or the restriction of T. gondii by IFN-gamma-treated macrophages, and did not have any effect of its own regarding these latter functions.