Virulence factors determine attachment and ingestion of nonopsonized and opsonized Bordetella pertussis by human monocytes

In the present study, the role of virulence factors in and the effect of opsonization on the interactions between Bordetella pertussis and human monocytes were investigated. The methods used facilitated the distinction between attachment and ingestion of bacteria by monocytes. Nonopsonized virulent B. pertussis cells attached to monocytes. Nonopsonized B. pertussis mutant strains deficient in filamentous hemagglutinin, fimbriae, or pertactin exhibited a reduced adherence to monocytes compared with that of their respective parental strains. Nonopsonized avirulent B. pertussis cells did not attach to monocytes. These results led to the conclusion that fimbriae and pertactin are involved in the adherence of nonopsonized virulent B. pertussis cells to monocytes and confirm the role of filamentous hemagglutinin in this process. In the absence of opsonins, about 40% of the monocyte-associated virulent B. pertussis cells were ingested. When B. pertussis cells were preopsonized with inactivated normal serum, about 50% of the monocyte-associated virulent B. pertussis cells were phagocytosed and about 80% of the monocyte-associated avirulent B. pertussis cells were ingested. These results indicate that virulence factors inhibit opsonin-mediated ingestion of B. pertussis by monocytes.