CLINICAL AND SEROLOGICAL EVALUATION OF A PASTEURELLA-HAEMOLYTICA A1 CAPSULAR POLYSACCHARIDE VACCINE

The purified capsular polysaccharide (CPS) of Pasteurella haemolytica Al was examined for its ability to protect cattle from experimental ch allenge with logarithmic-phase P. haemolytica. Several preparations of P. haemolytica antigens were utilized in the experiment including CPS , log-phase P. haemolytica culture supernatant, P. haemolytica recombi nant leucotoxin (rLKt) and various combinations of the above. CPS alon e or in combination with culture supernatant or rLkt elicited no prote ction; rather, administration of CPS was associated with a high incide nce of anaphylaxis (36% of calves). Although a classical biphasic humo ral immune response to CPS could be detected in all calves that receiv ed this compound, this T-dependent response was not correlated with re sistance to experimental challenge. The complexity of protective immun ity in pneumonic pasteurellosis is emphasized by this study, and clini cal anaphylaxis associated with response to CPS may be implicated in t he pathogenesis of disease.