Copyright C 1992, American Society for Microbiology Characterization of a Major Hemagglutinin Protein from

Mycoplasma gallisepticum cell membranes were used to immunize mice to produce monoclonal antibodies to cell surface proteins. Three monoclonal antibodies were chosen for further characterization. All three reacted in immunoblots with an M. gaUlisepticum protein band of Mr approximately 67,000 (designated pMGA). By using immunoelectron microscopy, pMGA was shown to be located on the cell surface. When M. gallisepticum whole cells were treated with up to 250 pg of trypsin per ml for 30 min, the only major protein lost from the cell surface as judged by sodium dodecyl sulfate-polyacrylamide gel electrophoresis followed by Western immunoblot transfer was pMGA. Two of the pMGA-specific monoclonal antibodies inhibited hemagglutination of chicken erythrocytes by M. gallisepticum S6, suggesting a role for pMGA in the attachment of M. galisepticum to chicken erythrocytes. Sequencing the amino terminus ofpMGA yielded 17 amino acids with no significant homology with the Mycoplasma pneumoniae attachment protein P1 or any other protein in the GenBank, Swiss-Prot, and EMBL data bases. The avian pathogen Mycoplasma gallisepticum is one of a number of mycoplasmas that cause respiratory disease. The physicochemical similarities of host cell receptors in M. pneumoniae (a cause of atypical pneumonia in humans) an