SERUM ANTIBODY-RESPONSES OF CATTLE TO IRON-REGULATED OUTER-MEMBRANE PROTEINS OF PASTEURELLA-HAEMOLYTICA A1

Serum antibody responses to the 70, 77, and 100 kDa iron-regulated out er membrane proteins (IROMPs) of Pasteurella haemolytica Al were studi ed in cattle vaccinated with outer membrane protein (OMP) enriched out er membrane fraction, IROMP-enriched outer membrane fraction or live P . haemolytica. Vaccination with an IROMP-enriched outer membrane fract ion stimulated antibodies to the 70 kDa IROMP, whereas vaccination wit h live P. haemolytica stimulated antibodies to the 70 and 77 kDa IROMP s. In a second experiment, sera were used from cattle vaccinated with live or killed P. haemolytica and subsequently challenged. Significant antibody responses to OMP- and IROMP-enriched outer membrane fraction s were detected by an enzyme-linked immunosorbent assay (ELISA) for ca ttle vaccinated with bacterins or live P. haemolytica. Regression anal ysis indicated significant correlations between high antibody response s to the OMP- or IROMP-enriched fraction and resistance to challenge. Antibody responses to the 70 and 77 kDa IROMPs were significantly grea ter for the live P. haemolytica vaccinates than for PBS control vaccin ates. There was no significant correlation between antibody responses to individual IROMPs and resistance or susceptibility to challenge. Th ese data suggest that antibodies to IROMPs alone are probably not resp onsible for protective immunity against pneumonic pasteurellosis. Anti bodies to IROMPs, however, in conjunction with antibodies to other sur face antigens probably enhance immunity to P. haemolytica challenge.