MYCOPLASMA-SYNOVIAE HAS 2 DISTINCT PHASE VARIABLE MAJOR MEMBRANE-ANTIGENS, ONE OF WHICH IS A PUTATIVE HEMAGGLUTININ

Mycoplasma synoviae is a major pathogen of poultry, causing synovitis and respiratory infection, A cluster of 45- to 50-kDa membrane protein s is immunodominant in strain WVU-1853, Four distinct proteins were id entified in this cluster by high-pressure liquid chromatography, Monoc lonal antibodies and monospecific antisera against each established th at they fell into two groups, MSPA and MSPB, each containing two membe rs distinguishable by a difference in hydrophobicity. A 25- to 30-kDa membrane protein (MSPC) was shown to be antigenically related to the M SPB proteins. Considerable variation in the size and expression of MSP A and MSPB was observed among different strains of M. synoviae. Examin ation of expression in colonies of strain WVU-1853 established that bo th MSPA and MSPB (and MSPC) were phase variable, Immunostaining of MSP B (and MSPC) with monoclonal antibodies exhibited quantal variation, w ith three distinct levels observed between and within colonies. Hemads orption by M. synoviae colonies was also found to be phase variable, w ith some colonies exhibiting sectorial expression of hemadsorption. Mo nospecific antisera against MSPA inhibited hemagglutination, but neith er monoclonal antibodies nor monospecific antisera against MSPB could inhibit hemagglutination, However, loss of the capacity to hemadsorb b y individual clones was associated with loss of expression of both MSP A. and MSPB. These findings have elucidated the complexity of structur e, function, and expression of the 45- to 50-kDa membrane protein clus ter of M. synoviae, and they suggest that all members of the cluster m ay be involved in adhesion.