Biomaterial centered infection is an important cause of the failure of prosthetic implants and organs. Almost all such infections, early and late, occur in the periprosthetic space and are caused by low levels of contamination with microbes implanted at the time of surgery. The inability of the host to eliminate relatively few bacteria is most likely due to failure of oxidative killing by the neutrophil in the presence of the foreign body. We have carefully explored, in the previous grant period, the direct interactions between neutrophilic respiratory burst and various biomaterials. Our evidence and that of others supports the idea that proteins adsorbed to certain polymers bind to specific receptors on the neutrophil and prime it to excessive production of reactive oxygen intermediates (ROI) when triggered by contaminating bacterial products (Staphylococcus or lipopolysaccharide) or inflammatory cytokines like tumor necrosis factor. As a result of excessive production of ROI, the neutrophils are likely to be impaired in their capacity to kill bacteria. In support of this idea is the fact that may adsorbed proteins can not only bind and prime neutrophils, but they can also specifically bind (opsonize) bacteria and bacterial products. Such proteins include the plasma protein (fibrinogen), the extracellular matrix proteins (fibronectin, laminin), the platelet derived protein (thrombospondin), and lipopolysaccharide binding protein (LBP). The prosthetic surface would then become a platform for infection because it adsorbs proteins which both bind the bacteria and the neutrophil into a configuration which leads to massive and prolonged production of ROI which in turn downregulates oxidative killing. Furthermore, such a complex biomaterial/protein/bacterial surface is likely to stimulate macrophages: 1) to secrete cytokines which will downregulate phagocytic killing; and 2) to secrete nitric oxide which has the capacity to react with and quench the ROI needed to kill bacteria. The present proposal is designed to systematically elucidate the interactions between a few selected biomaterials and suspect opsonic proteins in order to determine how such proteins bind to biomaterial and how the complexes fix bacteria to the polymeric surface. Once it becomes clear that certain opsonic proteins can be adsorbed onto biomaterials and bind bacteria there, the effects of the biomaterial/protein/bacterial complex on neutrophil and macrophage responses can be determined. The ultimate goal is a more complete understanding of the net effect of these interactions on oxidative killing of bacteria in the presence of a prosthetic implant.
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