Staphylococcus aureus can cause a variety of acute and chronic diseases. The ability of S. aureus to cause persistent infections has been linked to its ability to evade or inactivate host immune responses. We have identified a secreted 19-kDa protein produced by S. aureus that binds to the complement protein C3. N-terminal sequencing of this protein identified it as the extracellular fibrinogen-binding protein (Efb). In this study, we demonstrate that Efb can bind to the alpha -chain of C3 and inhibit both the classical and alternative pathways of complement activation. In addition, we show that Efb can inhibit complement-mediated opsonophagocytosis in a dose-dependent manner and that Efb inhibits complement activity by blocking deposition of C3 or by preventing further complement activation beyond C3b. These data suggest that Efb is a virulence factor involved in facilitating persistent S. aureus infections by interfering with complement activity in vivo.

A number of strategies have been investigated to enhance the mechanical stability of engineered tissues. In this study, we utilized lysyl oxidase (LO) to enzymatically crosslink extracellular matrix (ECM) proteins, particularly collagen and elastin, to enhance the mechanical integrity of the ECM and thereby impart mechanical strength to the engineered tissue. Vascular smooth muscle cells (VSMCs) were liposomally transfected with the LO gene. Both Northern and Western analyses confirmed increased LO expression. Increased LO activity was demonstrated using a fluorescent enzyme substrate assay and by observation of the presence of increased levels of desmosine, a product of LO crosslinking, in the ECM. The mechanical effects of altered crosslink densities within tissue-engineered constructs were demonstrated in a VSMC-populated collagen gel model. When smooth muscle cells transfected with lysyl oxidase were seeded in collagen gels, the tensile strength and elastic modulus in these constructs increased by approximately two-fold compared to constructs seeded with mock-transfected VSMCs. Also, desmosine levels in the LO-populated collagen gels were higher than they were in mock-seeded gels, as demonstrated via immunohistochemical staining. Compositional analysis of the ECM deposited by the transformed cells showed similar collagen and elastin levels, and cell proliferation rates were similar as well, thus attributing increased mechanical properties to ECM crosslinking.

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