Protective effect of two Mycoplasma gallisepticum protein fractions affinity purified with monoclonal antibodies

Two protein fractions of Mycoplasma gallisepticum (Mg) were affinity purifi ed with monoclonal antibodies A3 and B3, and tested for protective capacity in chickens. One fraction, designated MgP1, appeared as a doublet of 64 an d 62 kDa bands in sodium dodecyl sulphate-polyacrylamide gel electrophoresi s gels, while MgP2 consisted of five polypeptides (64, 56, 47, 45 and 43 kD a). The molecular mass, haemagglutination activity and matching amino acid sequence of MgP1 suggest that it is identical to pMGA1.2, the putative haem agglutinin of Mg. Groups of Mg-free chickens were immunized once or twice with 1 or 5 mu g Mg P1 or MgP2, or a combination of the two, and adjuvanted with immunostimulat ing complexes. Except for the group given 1 mg MgP1, all vaccinated groups showed a significant (P < 0.01) reduction in air sac lesions after challeng e compared with unvaccinated controls. MgP2 appeared more protective than M gP1. Vaccination twice with MgP2 was the only regime that produced a detect able serum antibody response.