The beta 2 integrins (LFA-1, Mac-1, and p150,95) are critical for many adhesive functions of leukocytes. Although the binding of the IgG-opsonized particles occurs normally in the absence of beta 2 integrins, phagocytosis of IgG-opsonized particles by activated neutrophils (PMN) requires these integrins. This observation suggests a role for beta 2 integrins in phagocytosis subsequent to particle binding. To investigate the mechanism of involvement of beta 2 integrins in IgG-mediated functions, we examined the role of beta 2 integrins in adhesion to immune complex (IC)-coated surfaces. Initial adhesion and spreading on IC-coated surfaces were equivalent in control and beta 2-deficient phagocytes. However, both genetically beta 2-deficient PMN and PMN treated with the anti-beta 2 mAb IB4 subsequently detached from the IC-coated surfaces. To determine whether biochemical consequences of IgG activation were also affected by beta 2 deficiency, LTB4 production in response to Fc receptor ligation was assessed. LTB4 production by beta 2-deficient PMN adherent to IC-coated surfaces was markedly decreased in comparison with control PMN. Importantly, LTB4 production by PMN stimulated with fluid phase heat-aggregated IgG also required the beta 2 integrins, showing that the defect was not a simple consequence of abnormal adhesion. In contrast, superoxide production by IC-adherent PMN was equivalent in control and beta 2-deficient PMN. The initial rises in intracytoplasmic [Ca2+]i in response to aggregated IgG also were unaffected by inhibition of beta 2 integrins. These data show that lack of beta 2 integrins does not inhibit all FcR-dependent signal transduction. Finally, LTB4 production by normal PMN adherent to ICs was inhibited by antibodies to FcRII, but not FcRIII, showing that FcRII ligation was required for this effect. Together these data identify a role for the beta 2 integrins in a signal transduction pathway leading to sustained adhesion and LTB4 production in response to IC. Since both beta 2 integrins and FcRII are required for these effects, the data further suggest cooperation between these receptors in generating PMN activation in response to IC stimulation.

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