Clearance of Bordetella parapertussis from the lower respiratory tract requires humoral and cellular immunity

Bordetella parapertussis and Bordetella pertussis are closely related species that cause whooping cough, an acute, immunizing disease. Their coexistence in the same host populations at the same time and vaccine studies showing that B. pertussis vaccines have little effect on B. parapertussis infection or disease suggest that the protective immunity induced by each does not efficiently cross protect against the other. Although the mechanisms of protective immunity to B. pertussis have been well studied, those of B. parapertussis have not. The present study explores the mechanism by which B. parapertussis is cleared from the lower respiratory tract by anamnestic immunity. Serum antibodies are necessary and sufficient for elimination of this bacterium, and CD4⁺ T cells, complement, and neutrophils are required for serum antibody-mediated clearance. Mice lacking immunoglobulin A had no defect in their ability to control or clear infection. Interestingly, serum antibody-mediated clearance of B. parapertussis did not require Fc receptors that are required for antibody-mediated clearance of B. pertussis. Together these data support a model for the mechanism of protective immunity to B. parapertussis that is similar but distinct from that of B. pertussis.