Characterization of bactericidal immune responses following vaccination with acellular pertussis vaccines in adults

Sera from six adults, collected before and after acellular pertussis vaccin ation, and from a placebo control were examined for the ability to elicit t wo bactericidal immune defenses, (i) antibody-dependent complement-mediated bacterial lysis and (ii) opsonization and phagocytosis by human neutrophil s. The samples were chosen based on low preimmunization titers and strong p ostimmunization responses to various combinations of vaccine antigens. All but two prevaccination samples demonstrated activity indicative of compleme nt-mediated lysis. Preimmunization activity could have been due to prior in fection or childhood immunization. Immunization did not result in improved bactericidal activity for any of the individuals, and in two cases immuniza tion caused a statistically significant decrease in complement-mediated lys is. Similarly, opsonization,vith the postimmunization sera failed to enhanc e attachment or phagocytosis of bacteria by neutrophils, and one postimmuni zation sample with a strong response to filamentous hemagglutinin caused an inhibition of phagocytosis that was statistically significant compared to that observed for the no-serum control. In summary, booster immunization of adults,vith acellular pertussis vaccines was not found to increase bacteri cidal activity over preimmunization levels. Identifying ways to promote bac tericidal immune responses might improve the efficacy of acellular pertussi s vaccines.