IFN gamma and TNF alpha cause an increased release of C3 by murine macrophages

Macrophages from mice bearing Lewis lung carcinoma release higher amounts of C3 molecules than macrophages from healthy mice. The C3 pro-releasing activity operating in vivo was suspected to be due to an immunological network. Indeed, the supernatants of splenocytes from tumor bearing mice, but not from normal mice, induced in vitro an increased release of C3 molecules by macrophages. Recombinant IFN gamma and TNF alpha were strong inducers of C3 release, while IL-2 acted poorly. The C3 pro-releasing activity of splenocyte supernatants was largely prevented by their pretreatment with specific mAb anti IFN gamma or anti TNF alpha, but not completely prevented by the simultaneous neutralization of the two cytokines. Taken together, these results show that murine macrophages increase the release of C3 molecules upon treatment with IFN gamma or TNF alpha and that these cytokines released in vivo by splenocytes from tumor bearing mice may account, together with a yet unknown factor, for a humoral network causing the increased release of C3 by peritoneal macrophages.