ANTIBODY-RESPONSES OF CATTLE TO OUTER-MEMBRANE PROTEINS OF PASTEURELLA-MULTOCIDA A-3

Objective-To quantify the serum antibody responses to Pasteurella mult ocida A:3 outer membrane proteins (OMP) for cattle vaccinated with the homologous serogroup and to correlate those responses with the extent of experimentally induced pneumonia. Animals-29, 5- to 8-month-old be ef-type calves. Procedure-Calves were vaccinated SC or by aerosol expo sure on days 0 and 7 with live or killed P multocida or phosphate-buff ered saline solution (control) and subsequently challenge exposed with virulent P multocida. Antibody responses to P multocida A:3 outer mem branes were quantified, using an ELISA. Antibody responses to individu al OMP were detected by immunoblot analysis (western blot) and were qu antified by densitometry. Antibody responses were compared among group s of calves and for various times after vaccination. Regression analys es were used to determine whether significant correlations existed bet ween lesion scores and antibody responses to either whole outer membra nes or to individual OMP. Results-By ELISA, antibody responses to oute r membranes for calves aerosol vaccinated with live P multocida were s ignificantly (P < 0.05) greater than those for control calves or for k illed P multocida vaccinates. There was a significant (P < 0.05) corre lation between lesion score and antibody responses to outer membranes. By western blotting and densitometry, antibodies to 11 prominent OMP (100, 97, 90, 85, 74, 53, 46, 35, 32, 21, and 16 kd) were identified a nd quantified. In experiment 1, SC vaccination with live P multocida i ncreased antibody binding to all protein bands except 85-, 74-, and 35 -kd bands, Aerosol vaccination with live P multocida stimulated increa ses in antibody binding to all bands except 100 and 16 kd. Antibody re sponses to the 97-, 90-, 74-, and 35- kd bands were significantly (P < 0.05) greater for live aerosol vaccinates than for control carves. In experiment 2, antibody responses were not different between the kille d P multocida vaccinates or control calves. Antibody responses for liv e P multocida aerosol vaccinates were significantly (P < 0.05) greater than those for control calves for the 100-, 90-, 85-, 74-, 53-, 35-, and 16-kd bands. Regression analyses indicated significant correlation s (P < 0.05) between lesion score and antibody responses to the 100-, 90-, 53-, 46-, 35-, and 32-kd OMP. Conclusions-Several OMP of P multoc ida type A:3 may be important for stimulating immunity to the organism in cattle.