Examination of the role of the αvβ3 and αvβ5 integrins in mediating vitronectin induction of microglial activation. Wild-type, β3 integrin KO, β5 integrin KO and β3/β5 integrin DKO microglia were purified from mixed glial cultures as described in Materials and Methods, and then cultured in serum-free medium on uncoated plastic, fibronectin or vitronectin. After 2 days culture, levels of MMP-9 in the microglial supernatants were examined by gel zymography. A. Representative gel zymogram. B. Summary of zymography experiments. Each point is expressed as the percentage change in MMP-9 relative to control (wild-type microglia on uncoated plastic) and represents the mean ± SD of three separate experiments. Note that culture on fibronectin and vitronectin increased MMP-9 expression in microglia from all strains of mice, with no obvious differences detected between wild-type and integrin KO strains on any substrate. C. Examination of the role of the αvβ3 and αvβ5 integrins in mediating microglial phagocytosis. Microglia from all 4 strains were purified as described in Materials and Methods, and cultured in serum-free medium on uncoated plastic for 24 hours before 2 μl of vitronectin-coated yellow-green fluorescent 2 μm beads were added to the cultures. 24 hours later cultures were washed to remove undigested beads and the microglial uptake of fluorescent beads examined by flow cytometry. Each point is expressed as the mean fluorescent index of the microglial population, and represents the mean ± SD of three experiments. Note that none of the integrin null microglia showed defects in their ability to phagocytose vitronectin-coated beads.