Production of the third and fourth component of complement (C3, C4) by smooth muscle cells

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Abstract
Production of the third and fourth components of complement (C3, C4) by smooth muscle cells was investigated by using normal human aortic smooth muscle cells (AoSMC), human smooth muscle cell line (G402) and vascular smooth muscle cells obtained from human umbilical cord vein (UVSMC). AoSMC spontaneously produced both C3 and C4 at 15 ng/10(6) cells/72 hr and 22 ng/10(6) cells/72 hr, respectively, and both were enhanced by interferon-gamma (IFN-gamma). Although phorbol 12-myristate 13-acetate (PMA) and tumour necrosis factor-alpha (TNF-alpha) enhanced C3 production, C4 production was reduced by these agents. On the other hand, G402 produced C4 but not C3 in a dose-dependent manner when cultured with IFN-gamma. UVSMC produced only a small amount of C3 and C4 compared with AoSMC or G402. C3 and C4 produced by AoSMC were confirmed to be identical with their human serum counterparts as determined by sodium dodecyl sulphate-polyacrylamide gel electrophoresis and measurement of haemolytic activity. Northern blotting analysis showed that the expression of mRNA of C3 and C4 was enhanced by TNF-alpha and IFN-gamma, respectively, in AoSMC. Our findings suggest the importance of smooth muscle cells as a source of components of complement in vascular diseases including vasculitis.