Respiratory burst in murine peritoneal macrophages: Differential sensitivity to phorbol diesters by macrophages in different states of functional activation

Abstract

Activation of macrophages either in vivo or in vitro can modulate the capacity to generate and secrete reactive oxygen intermediates including H 2O 2 and O 2 −. Thus, the cellular and biochemical components requisite for execution of the respiratory burst must be regulated during the activation process. In the present report, we have examined murine peritoneal macrophages in different stages of activation for their sensitivity to stimulants of respiratory burst known to activate protein kinase c (i.e., phorbol dibutyrate or diacylglycerol). The results demonstrated that more highly activated macrophages showed, in addition to greater magnitude of H 2O 2 or O 2 − production, a two- to fourfold greater sensitivity to these stimuli. While more active macrophages also exhibited a higher rate of H 2O 2 secretion, the time at which secretion was measured did not account for or modulate the heightened sensitivity. The increased sensitivity to stimulation was dependent upon the stage of activation and not on the agent used to elicit the macrophages. Increased sensitivity of the more active macrophage populations was also seen when physiologic stimuli (i.e., insoluble immune complexes or unopsonized zymosan) were used. These findings indicate that macrophage activation for H 2O 2 secretion modulates the sensitivity to stimulation such that more H 2O 2 is produced in a shorter time and at a lower concentration of stimulus, thereby heightening the inflammatory response in several independent ways. Because all the stimuli employed in the present study have in common the ability to activate protein kinase c (either directly or indirectly), the data also suggest that this form of macrophage activation may involve, at least in part, modulation of the stimulus-response coupling mechanisms which utilize this enzyme.