Immunochemical characterization of a heat-stable surface antigen of Mycoplasma pulmonis expressing both species-specific and strain-specific determinants.

We sought to characterize the strain-specific antigens of four strains of Mycoplasma pulmonis (47, 63, Negroni, and 19612) by crossed immunoelectrophoresis. Although the strains possessed a number of common antigens, type-specific antigens of 0.32 mobility (bovine albumin was assigned a value of 1) were detected in strains 47 and 63. Strains 19612 and Negroni cross-reacted and represented a third group. Each strain possessed a major heat-stable antigen complex of 0.32 mobility characterized by a faster-moving component of 0.55 mobility. Monospecific antiserum to heat-stable antigen 0.32 of strain 63 demonstrated that this antigen complex consisted of at least three antigen-antibody precipitating systems characterized by type-specific and group-specific determinants. Adsorption of antiserum with whole cells revealed that the 0.32 antigen complex was surface exposed. The antigen complex is pronase sensitive and only partially sensitive to periodate. Purification of antigen 0.32 from detergent-extracted cells by affinity chromatography using monospecific antiserum revealed two major polypeptides of 86,500 and 83,500 dalton which reacted strongly with monospecific antiserum by immunoblotting. These reactive polypeptides were present in all strains examined. Additional polypeptides of different molecular weights in strains 19612 and Negroni produced strong reactions with monospecific antiserum, although sodium dodecyl sulfate-polyacrylamide gel electrophoresis profiles of the two strains were strikingly similar. Common heat-stable antigens were observed also. This study demonstrates that M. pulmonis strains possess an antigenically variable heat-stable surface antigen which is unique in that it contains not only strain-specific determinants but also species-specific determinants.