Vitronectin modulates the expression of complement components of the terminal pathway synthesized by human umbilical vein endothelial cells in vitro

In this study we demonstrate that human endothelial cells (EC) synthesize mRNA for vitronectin by using techniques based on reverse transcriptase (RT) reaction and polymerase chain reaction (PCR). The identification of vitronectin mRNA, shown by sequence analysis of PCR‐amplified RT product of RNA extracted from EC, clearly demonstrates that these cells synthesize mRNA for vitronection. We further investigated whether vitronectin in serum‐free EC cultures regulates the net expression of the terminal complement pathway, measured as the terminal complement complex (TCC) bound to co‐cultured agarose beads which activate the alternative pathway. Presence of polyclonal F(ab‘)2 anti‐human vitronectin (VN) antibodies, regardless of concentration (10–80 μg/ml), significantly reduced the binding of monoclonal anti‐C3c antibodies to co‐cultured beads, whereas the binding of monoclonal anti‐TCC antibodies was unaltered or significantly increased compared with controls. Despite some interexperimental variation in the results, addition of vitronectin (10–80 μg/ml) to the EC resulted in an inversely related pattern compared with experiments using anti‐VN antibodies. The binding indices of anti‐C3c are comparable to the controls. On the other hand, there is a steady concentration‐dependent (10–80 μg of vitronectin added) reduction in binding of anti‐TCC up to approximately 60%. The results indicate that vitronectin regulates the expression of synthezised and surface‐bound TCC in serum‐free EC cultures, comparable to previous findings in serum.