Influence of CR3 (CD11b/CD18) expression on phagocytosis of Bordetella pertussis by human neutrophils

CR3 (CD11b/CD18) is expressed on neutrophils, and the engagement of CR3 can promote phagocytosis. CR3 serves as the receptor for the Bordetella pertussis adhesin filamentous hemagglutinin (FHA) and for the adenylate cyclase toxin (ACT), which blocks neutrophil function. The influence of CR3, FHA, and ACT on the phagocytosis of B. pertussis by human neutrophils was examined. The surface expression and function of CR3 are regulated. Tumor necrosis factor alpha (TNF-alpha) and gamma interferon (IFN-gamma) increased CR3 surface expression, but only TNF-alpha increased the ability of neutrophils to phagocytose B. pertussis, suggesting that elevated CR3 expression alone is not sufficient to promote phagocytosis. Purified FHA and pertussis toxin also increased the surface expression of CR3 on neutrophils, while ACT and the B subunit of pertussis toxin did not affect CR3 expression. FHA-mediated attachment to CR3 can lead to phagocytosis, especially in the absence of ACT. FHA mutants failed to attach and were not phagocytosed by neutrophils. Similarly, an antibody to CR3 blocked both attachment and phagocytosis. The addition of exogenous FRA enhanced the attachment and phagocytosis of wild-type B. pertussis and FHA mutants. Mutants lacking the SphB1 protease, which cleaves FHA and allows the release of FRA from the bacterial surface, were phagocytosed more efficiently than wild-type bacteria. ACT mutants were efficiently phagocytosed, but wild-type B. pertussis or ACT mutants plus exogenous ACT resisted phagocytosis. These studies suggest that the activation and surface expression of CR3, FRA expression, and the efficiency of ACT internalization all influence whether B. pertussis will be phagocytosed and ultimately killed by neutrophils.