Potential subunit vaccine against Mycoplasma pulmonis purified by a protective monoclonal antibody

Monoclonal antibodies (mAbs) were produced against Mycoplasma pulmonis (MP); some were highly protective in the treatment of experimental infections of BALB/c mice. The mAbs inhibited MP growth in vitro and prevented the attachment of MP to fibroblasts or to red blood cells. Three separate mAbs recognized 54-76% of 54 clinical isolates of MP, and the three together detected all 54 isolates. We used the mAbs to purify the antigens by affinity column chromatography. The purified antigen used to vaccinate mice and to immunize rabbits produced antibodies capable of significant growth inhibition in sera and tracheolung lavage fluids. The vaccinated mice were challenged with various doses of a highly virulent T2 strain of MP. Assays for viable MP organisms and for histopathological changes in the lungs of infected mice indicated that mice were protected if the challenge dose was 10³-10⁵, but not 10⁷, c.f.u. The sera of immunized rabbits were used to passively transfer immunity to mice. The sera provided complete protection against 1 × 10⁶ c.f.u. T2 MP. We conclude that MP antigens purified by this protocol can provide a safe vaccine against this disease, at least in mice.