Pertussis antibodies in the sera of children exposed to Bordetella pertussis by vaccination or infection.

Low agglutinin titres to pertussis suspensions were found in 99% of sera from a group comprising healthy adults and non-vaccinated, non-infected infants of 1-6 months of age. These are attributable to agglutinins to heat-stable antigens and/or heat labile agglutinogen 1, and cross-absorption tests must be done on the sera in order to distinguish between the two. Agglutinins to agglutinogens 2 and 3 were found in only about 20% of adult sera. Bactericidal antibody was low in titre or absent in all sera from non-exposed individuals.Raised bactericidal antibody titres and the presence of agglutinins 2 and 3 were attributed to exposure to Bordetella pertussis antigens, either as vaccine or as infection. The variation, amongst both vaccinated and infected children, was very great. A vaccinated child who became ill responded to the infection in much the same way as a non-vaccinated child. We were unable to relate the immunity of the child to the titres either of agglutinins or of the bactericidal antibody.The protective ability of sera from vaccinated or infected children measured in mice against small, lethal brain infections was also unrelated to the state of immunity in the children, but this protective ability was correlated with the complement-mediated bactericidal antibody titres of the sera.The distribution of agglutinins, bactericidal antibody, and anti-haemagglutinin in serum IgG and IgM was different in vaccinated and infected children.