EFFECT OF GAMMA-INTERFERON ON THE SYNTHESIS OF THE FUNCTIONAL ALTERNATIVE AND TERMINAL COMPLEMENT PATHWAYS BY HUMAN UMBILICAL VEIN ENDOTHELIAL-CELLS IN-VITRO

The cytokine gamma-interferon (gIFN) has been reported to modulate syn thesis by endothelial cells (EC) of alternative pathway complement fac tors (H, I, and B). However, the net effect of gIFN on the synthesis a nd expression of the functional alternative and terminal pathways has not yet been reported. EC cultured under serum-free conditions were tr eated with different concentrations of gIFN and simultaneously co-incu bated with agarose beads, which activate the alternative pathway. C3b and the terminal complement complex (TCC) bound to co-incubated beads were measured by radioimmunoassay using anti-human C3c and TCC antibod ies. gIFN in concentrations 500-4000 U/ml increasingly reduced the amo unt of C3b and Tcc detected on the beads. The down-regulating effect o f gIFN on EC complement biosynthesis may be physiologically relevant b y locally controlling complement activation.