Antibody responses of cattle to outer membrane proteins of Pasteurella multocida A:3

OBJECTIVE: To quantify the serum antibody responses to Pasteurella multocida 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 beef-type calves. PROCEDURE: Calves were vaccinated SC or by aerosal exposure on days 0 and 7 with live or killed P multocida or phosphate-buffered saline solution (control) and subsequently challenge exposed with virulent P multocida. Antibody responses to P multocida A:3 outer membranes were quantified, using an ELISA. Antibody responses to individual OMP were detected by immunoblot analysis (western blot) and were quantified by densitometry. Antibody responses were compared among groups of calves and for various times after vaccination. Regression analyses were used to determine whether significant correlations existed between lesion scores and antibody responses to either whole outer membranes or to individual OMP. RESULTS: By ELISA, antibody responses to outer membranes for calves aerosol vaccinated with live P multocida were significantly (P < 0.05) greater than those for control calves or for killed P multocida vaccinates. There was a significant (P < 0.05) correlation 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 and quantified. In experiment 1, SC vaccination with live P multocida increased antibody binding to all protein bands except 85-, 74-, and 35-kd bands. Aerosol vaccination with live P multocida stimulated increases in antibody binding to all bands except 100 and 16 kd. Antibody responses to the 97-, 90-, 74-, and 35- kd bands were significantly (P < 0.05; greater for live aerosol vaccinates than for control calves. In experiment 2, antibody responses were not different between the killed P multocida vaccinates or control calves Antibody responses for live 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 correlations (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 multocida type A:3 may be important for stimulating immunity to the organism in cattle.