Capsulelike surface material of Mycoplasma dispar induced by in vitro growth in culture with bovine cells is antigenically related to similar structures in vivo.
Electron microscopy was used to show that M. dispar produces an external capsule-like material in vivo that has an affinity for both ruthenium red and polycationic ferritin. This extracellular material is lost during passage in culture medium but can be regained with a single passage on bovine lung fibroblast (BLF) cells. To confirm that the extracellular material associated with cell-grown mycoplasmas was the same as that observed in infected calves, rabbit antibodies were produced to purified capsule-like material isolated by protease digestion of cell-grown organisms. These antibodies bound to capsule-like material on the surface of M. dispar cells colonizing the bronchial epithelium of infected calves and to capsule-like material from cell-grown mycoplasmas. Calves infected with M. dispar produced antibodies in lung secretions that were capable of binding to the purified capsule-like material. The Fab fragments of rabbit antibody to in vitro-produced capsule-like material could block this binding, indicating that the capsule-like material was similar in both in vivo-grown and cell-grown organisms. The carbohydrate nature of the capsular material suggested by the ruthenium red and polycationic staining characteristics was confirmed by its binding to Ricinus communis agglutinin, a galactose-specific lectin. These results confirm that capsule material produced during infections with M. dispar share antigenic determinants with the material produced under in vitro conditions and that association with mammalian cells induces production of this material.