Antigenic analysis of iron-regulated proteins in Pasteurella haemolytica A and T biotypes by immunoblotting reveals biotype-specific epitopes.

The antigenic relationships of the iron-regulated proteins (IRPs) in Pasteurella haemolytica A and T biotype strains were examined by SDS-PAGE and immunoblotting. P. haemolytica cells of the A biotype, grown under conditions of iron-limitation, expressed two IRPs, of 35 and 70 kDa. All T biotype strains expressed IRPs with slightly different molecular masses of 37 and 78 kDa. Immunoblotting of all 16 P. haemolytica serotypes was carried out using a panel of polyclonal and monoclonal antibodies raised against serotype A2 antigens. Polyclonal antibodies revealed inter-serotype cross-reactivity towards the 35 and 70 kDa IRPs within the A biotype but no cross-reactivity against a T biotype protein in the 78 kDa region. Monoclonal antibody against the 35 kDa antigen reacted only with the A biotype 35 kDa IRP. Identical profiles were obtained for 10 field isolates of serotype A2, further emphasizing the antigen conservation within the A biotype. These findings reinforce the view that the A and T biotypes of P. haemolytica should be considered as separate species and suggest that IRPs from single A and T biotype strains incorporated into a vaccine might provide cross-protection against all P. haemolytica serotypable strains. Similar studies on the IRPs of 10 untypable strains revealed some of these to have different antigenic reactivities from those observed within the A and T biotypes.