Surface dependent human monocyte and macrophage adhesion and foreign body giant cell formation

Modern biomaterial design focuses on bio-active surface modifications which ensure beneficial biological interactions by targeting specific biochemical pathways. This study is intended to identify such pathways using a 10 day human monocyte culture protocol which fosters macrophage development and interleukin-4 (IL-4)-induced foreign body giant cell (FBGC) formation, as a model of the cellular arm of the inflammatory response surrounding implanted biomaterials. Previous use of this culture protocol has shown that the adhesion and fusion of human macrophages in vitro is strongly influenced by substrate chemistry. In the current study, alkyl-silane modified surfaces and polyethylene oxide (PEO)-coupled surfaces were successfully prepared, as confirmed by contact angle and XPS surface analysis. Human monocyte cultures revealed that the presence of surface bound long-chain alkanes and PEO molecules inhibited long term macrophage adhesion and IL-4-induced FBGC formation. In contrast, clean glass allowed high levels of macrophage adhesion while actively inhibiting FBGC formation. Using radiolabeled proteins, the composition of protein adsorption from human serum onto amino-, alkyl-, and PEO-modified surfaces was quantified. After comparing adsorption data with previously documented in vitro cellular responses, IgG, vitronectin (VN), and von Willebrand Factor (vWF) were identified as ligands whose adsorption may be involved in the surface dependence of macrophage adhesion and fusion. Macrophages cultured on IgG-, VN-, and vWF-preadsorbed surfaces confirmed that adsorbed IgG enhances long-term macrophage adhesion and adsorbed vWF inhibits long-term macrophage adhesion. The inhibitory effect of preadsorbed vWF could not be attributed to a specific macrophage receptor. However, antibody analysis demonstrated that beta3 integrins are responsible for the adhesion which does exist on preadsorbed vWF substrates. The biological activity of preadsorbed IgG was found not to be present in the Fc fragment, but rather within the Fab and F(ab')2 fragments. The possibility of an unknown macrophage Fab receptor was proposed, however neoglycoprotein inhibitor studies suggest that macrophage lectins specific for Fab-bound carbohydrates are involved in the effect of adsorbed IgG. Additionally, a photoirradiation technique for patterning macrophage adhesion on preadsorbed IgG substrates was demonstrated. This investigation into the in vitro surface dependent responses of human inflammatory leukocytes provided valuable insight into the molecular mechanisms of inflammation and the foreign body reaction, as a basis for future bio-active biomaterial design.