Mycoplasma pneumoniae vaccine: antigenicity of buffered antigens in volunteers.

The antigenicity of experimental Mycoplasma pneumoniae vaccines prepared from antigen grown in a medium buffered with N-2-hydroxyethylpiperazine-N'-2'-ethanesulfonic acid was tested in young, adult males. Formalin-inactivated antigens from a high-passage strain and a low-passage strain at various dilutions (12 to 123 mug of N/ml) were injected intramuscularly in 1-ml doses. Antibody responses were tested by the metabolic inhibition (MI) technique. Sixty-five to 86% of the volunteers in all vaccine groups responded with fourfold or greater MI antibody rises, but only nine (39%) of 23 antibody-free subjects converted compared to 53 (88%) of 60 of those with pre-existing antibody. A booster vaccination did not increase the number of converters or enhance the geometric mean titers. The antigen concentrations of vaccines with 24 or more mug of N/ml appeared to be above the threshold needed for maximal antibody responses in the dose range tested. MI antibody rises could not be detected in sputa and nasal washings obtained from a small group of vaccinees. The results of this study suggest that the new vaccines offer little or no improvement in antigenicity in man over earlier inactivated vaccines.