Evidence of bovine immunoglobulin G sub(1) (IgG sub(1)) protease activity in partially purified culture supernate of Pasteurella haemolytica A1

In the bovine respiratory tract, IgG sub(1) is a major secretory immunoglobulin (Ig), and both IgG sub(1) and IgG sub(2) are believed to be important in defense against pneumonic pasteurellosis (shipping fever) in calves. Here we provide evidence for hydrolysis of IgG sub(1) in the presence of partially purified culture supernate (ppCS) from the respiratory pathogen Pasteurella haemolytica A1. Bovine IgG sub(1) was hydrolysed sequentially into three distinct bands (approximately 39, 12, and 7 kDa respectively). Furthermore, partial hydrolysis of bovine IgG sub(2) was observed, but neither bovine IgA nor IgM were affected by incubation with ppCS. These findings suggest that the production of an IgG sub(1)-specific protease by P. haemolytica A1 may be a virulence mechanism contributing to the pathogenesis of bovine pneumonic pasteurellosis.