Serum IgG response to putative virulence factor Gs60 of Mannheimia haemolytica
Many bovine pneumonic pasteurellosis vaccines incorporate ' Mannheimia haemolytica' antigens, including the acknowledged virulence factor, leukotoxin (Lkt), and Gs60, a surface lipoprotein. To examine the role of antibodies to Gs60 in protection, an ELISA was developed for retrospective analysis of sera from previous trials where vaccines containing native or recombinant Gs60 were administered parenterally or via the oral route. This revealed a positive correlation between titer to Gs60 and protection against experimental challenge in both vaccinates and naturally exposed controls, although for one experimental edible vaccine the slope of regression fines suggested diminished protection if antibodies were induced by vaccination. There was a strong correlation between production of IgG to Gs60 and Lkt neutralizing antibodies. Including titers to Lkt and Gs60 in a linear model revealed higher impact for Lkt in protection; however, further analysis showed that antibodies against Gs60 were particularly beneficial when Lkt neutralizing titers were low.