The antibody activities of 19S and 7S fractions from rabbit antisera to Bordetella pertussis.

antisera were fractionated on Sephadex G-200 to give 19S and 7S globulins, the latter refractionated on DEAE-cellulose, and the antibody properties of the two purified materials compared. The minimal weights of 19S and 7S globulins required to neutralize haemagglutinin and to protect mice against an intranasal challenge causing lung infection were similar. In agglutination 7S globulin was 1.5–100 times more effective than 19S, the ratio depending on strain and serum, but there was no apparent correlation with specific agglutinogens. 7S globulin was at least 100 times more effective than 19S both in the complement-dependent bactericidal reaction and in the protection of mice against an intracerebral challenge. It is suggested that the two reactions measure the same antibody.