IN-VIVO VARIATION OF MYCOPLASMA-GALLISEPTICUM ANTIGEN EXPRESSION IN EXPERIMENTALLY INFECTED CHICKENS

The antigen expression profiles of Mycoplasma gallisepticum isolates o btained from tracheal swabs of chickens after aerosol-inoculation with M. gallisepticum strain R or clonal variant R/E were examined in west ern immunoblots. A reference anti-M. gallisepticum chicken antiserum a nd antisera from individual infected chickens as well as monoclonal an tibodies (mAbs) specific for surface proteins were used to monitor in vivo antigenic variation. mAbs 1E5 and 12D8, recognizing PvpA and p67a , recently shown to undergo high-frequency in vitro phase variation, w ere used for consecutive staining of colony and western immunoblots in order to distinguish between the resultant phenotypes with respect to the corresponding epitopes. Marked differences in the expression of m ajor immunogenic proteins, including p67a, were observed between the t wo inocula as well as among reisolates recovered at different times of infection. Comparative western immunoblot analysis of the rapidly cha nging chicken serum antibody response and reisolates recovered during the course of an experimental infection with M. gallisepticum R or clo nal variant R/E suggest that immune modulation may have a key role in generating surface diversity. In addition, comparison of colony immuno blots of strain R inoculum and of reisolated colonies from tracheas of birds 8 days post infection indicated an in vivo selection of the Pvp A(+)p67a(-) phenotype. This study established that surface antigens of M. gallisepticum are subjected in vivo to rapid alteration in their e xpression. This variability may function as a crucial adaptive mechani sm, enabling the organism to escape from the host immune defense and t o adapt to the changing host environment at different stages of a natu ral infection.