The Inability of the Capsular Material of Haemophilus pertussis to produce Protective Antisera

SUMMARY: Bacterial suspensions of capsulated Haemophilus pertussis, prepared from cultures freshly isolated from infected mice, or from Phase I strains maintained on Bordet Gengou medium, produced in rabbits antisera which contained specific agglutinating and complement-fixing antibodies and which protected mice against experimental pertussis infection. Organisms which had been washed three times with distilled water and freed from capsular material also produced similar antibodies. More than one antigen may be involved in the production of these antibodies.

On the other hand, bacilli-free preparations, containing the capsular material in a concentrated form, produced antisera with only low levels of agglutinating, complement-fixing and protective antibodies.

The experiments indicated that the antigens of H. pertussis which produced these antibodies are somatic rather than capsular.