Contribution of vascular catheter material to the pathogenesis of infection: depletion of complement by silicone elastomer in vitro.

We previously have shown that vascular catheters made of silicone elastomer carry a greater risk of subcutaneous infection with Staphylococcus aureus than do polyurethane (PU), polyvinylchloride (PVC), or Teflon catheters. We further have shown that there is greater inflammation surrounding silicone catheters than there is surrounding catheters made of the other materials, suggesting that silicone produces a greater chemotactic gradient than do the other materials. This study used a functional complement opsonization assay and radioimmunoassays to compare the relative abilities of silicone, polyurethane, and polyvinylchloride to activate complement. Serum incubated in silicone catheters for 24 h had less than 30% of the opsonizing ability of fresh serum while > or = 78% of the opsonizing ability remained with serum incubated in PU or PVC catheters. Measurement of C3a des Arg, C4a des Arg, C5a des Arg, and SC5b-9 demonstrated that the loss of opsonizing ability was due to 10-fold greater alternate pathway complement activation by silicone than by PU or PVC. This finding suggests that excessive complement activation by silicone may explain the greater inflammation seen around silicone catheters in vivo and also might play a role in silicone's creating a greater risk of infection.