Comparison of IgG Fc receptors from clinical isolates of Streptococcus zooepidemicus

Department of Veterinary Microbiology and Pathology, Washington State University, Pullman, Washington 99164-7040, USA Received May 26, 1988 Accepted July 25, 1988 A receptor binding the Fc region of equine immunoglobulin G (IgG) has been isolated from a heat-extracted preparation of a clinical isolate of Streptococcus zooepidemicus . This Fc receptor has a M r of 45 x 10 3 and was occasionally seen as an apparent trimer of M r 130 x 10 3 . Antibodies prepared in horses against the receptor could be adsorbed to and eluted from whole live bacteria, confirming the surface location of this protein. Another 11 isolates of S. zooepidemicus from horses with pneumonia, abscesses or endometritis were tested for Fc-receptor activity. Although the M r of the Fc receptors varied among isolates, their antigenicity was conserved. Thus, the Fc receptor is an attractive candidate for application in the diagnosis of, or protection against, infections with S. zooepidemicus .