Optimization of immunization schedule to standardize antibody response in mice to pertussis vaccines.

The intracerebral challenge test for determining the protective potency of pertussis vaccines has long been in use. In an effort to elucidate what antibodies are responsible for such protection, a study was undertaken to analyse serum antibodies against filamentous hemagglutinin, lymphocytosis promoting factor and agglutinogens. Conventional pertussis vaccines induced antibodies to FHA and agglutinogens in mice whereas no demonstrable antibodies to LPF were stimulated. By toxoiding LPF on cells with 0.4 per cent formaldehyde, preparations were obtained which induced anti-LPF antibodies in mice. This treatment however, resulted in considerable reduction in potency as judged by the intracerebral challenge test. Apparently the protective potency of pertussis vaccines in mice is based on the adjuvant properties of LPF and not its antigenic properties. An optimized schedule is outlined for the laboratory standardization of pertussis vaccines by measuring antibody responses and especially anti-LPF in mice. Highest titers were obtained in mice when the interval between immunization and booster injections was 28 days.