Kinetics of the Biosynthesis of Complement Subcomponent C1q by Murine Macrophages: Effects of Stimulation by Interferon-γ

The effects of interferon-γ(IFN-γ) on the kinetics of biosynthesis of complement subcomponent C1q by mouse inflammatory peritoneal macrophages were determined. Stimulation of macrophages with various concentrations of IFN-γ produced a dose-dependent increase in C1q mRNA accumulation which was detected as early as 3 h and sustained through 24 h, as determined by Northern blot analysis. A corresponding early increase in the extracellular accumulation of functional C1q was detected in culture supernatants after 3–9 h stimulation of macrophages with IFN-γ that was sustained for 24–48 h as determined by a complement hemolytic assay. Autoradiographic analysis of [35S]methionine-labeled secretory C1q confirmed the protracted dose-dependent secretion of C1q by IFN-γ stimulated macrophages during 24–48 h of culture. Western blot analysis of macrophage lysates indicated no significant changes in endogenous C1q levels following stimulation with IFN-γ either after 3–9 h or 24–48 h when both C1q mRNA and extracellular accumulation were at their peak. Our results indicate that IFN-γ promotes early and protracted mRNA accumulation and secretion of C1q by macrophages without intracellular accumulation, presumably due to the rapid rate of secretion of newly synthesized C1q. It is apparent that priming of macrophages with IFN-γ provides a rapid and abundant source of secretory C1q for potential interaction with various macrophage triggering agents which also bind C1q.