Protection against Bordetella pertussis in mice in the absence of detectable circulating antibody: implications for long-term immunity in children.

Most vaccines used for humans work through humoral immunity, yet many appear to be protective even after specific circulating antibody levels have waned to undetectable levels. Furthermore, it has been difficult to define a serologic correlate of protection against a number of infectious diseases, including those caused by Bordetella pertussis. B. pertussis clearance in immunized mice has been shown to correlate with pertussis vaccine efficacy in children. This murine respiratory challenge model was used to demonstrate persistent vaccine-induced protection against B. pertussis in the absence of circulating antibody at the time of challenge. Whole-cell and acellular pertussis vaccines induced persistent memory T and B cells and anamnestic antibody responses after challenge. The findings suggest that immunologic memory is more significant in protection than is the induction of immediate antibody responses and imply that vaccinated children still may be protected against disease following the disappearance of specific serum IgG.