Complement proteins in serum are mainly synthesized by hepatocytes. Re
cently, many cell types have been reported to synthesize complement in
various tissues. In this study, we report the synthesis and secretion
of the third component of complement (C3) by cultured glomerular epit
helial cells (GEC). Using reverse transcriptase polymerase reaction, w
e have found that GEC and whole kidney expressed the C3 mRNA for C3. B
y ELISA, we have found that C3 was secreted in culture supernatants ha
rvested from cultured GEC. The secretion of C3 is regulated by proinfl
ammatory cytokines (IL-1 beta, TNF-alpha and IL-6). IL-1 beta is shown
to be the most potent stimulator of C3 secretion from GEC. The exact
significance of C3 produced at glomerular site is not clear, but its u
pregulation by proinflammatory cytokines may suspect a role in local a
ctivation of complement which may lead to glomerular injury. We furthe
r studied the expression of C3 step regulatory proteins (membrane cofa
ctor protein (MCP), decay-accelerating factor (DAF), CR-1 and CD59 (a
terminal step regulatory protein) by cultured GEC. Treatment of GEC by
proinflammatory cytokines IL-1 beta, TGF-beta, TNF-alpha and IL-6 did
not modify the expression of MCP, DAF and CR-1 whereas an increase in
the expression of CD59 could be observed after treatment with IL-1 be
ta and TGF-beta. These results indicate that the expression of these r
egulatory proteins is tissue specific and may be implicated in inflamm
atory processes.