EVIDENCE FOR A COMMON EPITOPE ON THE SURFACE OF MYCOPLASMA-GALLISEPTICUM DEFINED BY MONOCLONAL-ANTIBODY

An antigen containing a common epitope in most strains of Mycoplasma gallisepticum was purified by isoelectric focusing and used in the production of monoclonal antibodies (mAb). Of several mAb produced, only one mAb reacted with focused component and with all six strains of. M. gallisepticum except strain 6/85. This mAb was designated MG3D6.A5, and it was subsequently purified with immobilized rProtein A(tm). The MG3D6.A5 mAb recognized a common epitope on a molecule with relative molecular weight of 98 kilodaltons (kDa), termed p98. No binding was observed when the MG3D6.A5 mAb was reacted against antigens extracted from other mycoplasma species, indicating its species-specificity. Physicochemical studies revealed that p98 had an isoelectric point of 5.2, was stable to heat, and was resistant to periodate oxidation but sensitive to trypsin treatment, suggesting that p98 is a nonglycosylated protein. Furthermore, ultrastructural studies with colloidal gold revealed that M. gallisepticum cells were selectively stained with MG3D6.A5 mAb to p98. The latter was focally distributed on the surface of a mycoplasma cell membrane near the attachment organelle. These results suggest that p98 is a highly conserved protein in M. gallisepticum strains, is immunogenic, and is surface-accessible; its binding specificity to MG3D6.A5 mAb could be used to identify M. gallisepticum in multiple cultures.