Poultry infected with Mycoplasma gallisepticum or Mycoplasma synoviae produce antibodies to their cysteine protease CysP

Major poultry pathogens, Mycoplasma gallisepticum and Mycoplasma synoviae possess cysteine protease CysP, which in vitro cleaves chicken immunoglobulin G (IgG) into Fab (antigen-binding fragment) and Fc (crystallisable region fragment). We used recombinant CysP of M. synoviae (rCysP) in enzyme immunoassays to detect antibodies to CysP in sera, synovial fluids, and in washings of respiratory tract and oviducts of chickens and turkeys experimentally or naturally infected with M. gallisepticum or M. synoviae. In poultry infected with M. synoviae, 70.4 % of samples contained antibodies reacting with rCysP. In birds infected with M. gallisepticum we detected CysP antibodies in 63.1 % of samples. Our data demonstrate that CysP is immunogenic for chickens and turkeys and indicate that M. gallisepticum and M. synoviae infecting chickens and turkeys synthesise CysP in vivo. This is the first study demonstrating that proteases of any Mycoplasma species can induce production of specific antibodies in the natural host.