Characterizion of Mycoplasma pulmonis variants isolated from rabbits. II. Basis for differentiation of antigenic subtypes.

The antigen composition of Mycoplasma pulmonis variants was studied by complement-fixation, agar-gel diffusion, and growth-inhibition tests. Two classes of complement-fixing antigens were demonstrated for M. pulmonis strains 47 and 63: (i) cross-related, heat-labile, water-soluble antigens, and (ii) high-titered, subtype-specific, heat-stable, water-soluble antigens. Lipid antigens prepared by organic solvent fractionation were low-titered antigens and showed little specificity. With the aid of agar-gel double-diffusion plates, the subtype-specific antigens were found to be precipitated by trichloroacetic acid and to be stable to periodate, but they were inactivated by pronase. Pronase-stable, periodate-labile precipitating antigens were observed as common components between the two variants. Antisera prepared with boiled antigens were found to be serologically active on gel diffusion but lacked neutralizing ability in growth-inhibition tests. Each of three strains of M. pulmonis (47, 63, ATCC 14267) could be identified as a variant because each strain possessed immunologically distinct heat-stable subtype-specific antigen(s).