SIALOGLYCOPROTEASE OF PASTEURELLA-HAEMOLYTICA A1 - DETECTION OF ANTISIALOGLYCOPROTEASE ANTIBODIES IN SERA OF CALVES

Log phase culture supernate from Pasteurella haemolytica biotype A, se rotype 1 contains a proteolytic enzyme specific for O-sialoglycoprotei ns. Using two methods, Western immunoblotting and enzyme neutralizatio n assay, it was demonstrated that certain bovine sera from two previou s P. haemolytica A1 vaccination and challenge trials contained antibod ies (Ab) (isotypes IgG(1) and IgG(2) on Western immunoblot) to the sia loglycoprotease (Gcp). In these trials, selected calves were vaccinate d twice with either the commercial culture supernate vaccine Presponse (R) or given phosphate-buffered saline (PBS). One trial was conducted during spring, P. haem XIX, and the other during the winter, P. haem X XI. Although there was no clear evidence for induction of anti-Gcp in response to vaccination, several calves seroconverted following intrap ulmonary challenge with live P. haemolytica A1. This is the first repo rt of anti-Gcp Ah in bovine sera. The results indicated that the Gcp i s immunogenic and that the bacterium produces the enzyme in vivo. Furt her, animals with an anti-Gcp response had less pneumonia at necropsy, suggesting the Gcp may induce protective immunity.