Intranasal vaccination of calves with Mannheimia haemolytica chimeric protein containing the major surface epitope of outer membrane lipoprotein PlpE, the neutralizing epitope of leukotoxin, and cholera toxin subunit B

This study was done to determine if intranasal vaccination of weaned beef calves with a chimeric protein containing the immunodominant surface epitope of Mannheimia haemolytica PlpE (R2) and the neutralizing epitope of leukotoxin (NLKT) covalently linked to truncated cholera toxin (CT) subunit B (CTB) could stimulate secretory and systemic antibodies against M. haemolytica while enhancing resistance of cattle against M. haemolytica intrabronchial challenge. Sixteen weaned beef calves were intranasally vaccinated with CTB-R2-NLKT chimeric (SAC102) or with R2-NLKT-R2-NLKT chimeric (SAC89) protein with or without native CT on days 0 and 14 and were challenged intrabronchially on day 28. In vitro, SAC102 bound the CT receptor molecule, GM1-ganglioside. Mean IgA antibodies to M. haemolytica whole cells (WC) and to LKT were high on day 0. A small, yet significant increase (p < 0.05) was found in mean nasal antibodies to M. haemolytica WC for the SAC89 + CT and SAC102 vaccinates after the second vaccination. SAC102 stimulated significant (p < 0.05) mean serum antibody responses to all three antigens by day 28. Following challenge, mean antibodies to WC and LKT significantly increased (p < 0.05) for the SAC102, SAC89 and SAC89 + CT groups with the mean antibody responses to rPlpE stimulated by SAC102 vaccination being significantly higher (p < 0.05) than for the other vaccinated and control groups. On day 1 after challenge, mean clinical score for the control group was significantly higher (p < 0.05) than for the SAC102 and SAC89 + CT vaccinates, and by day 2 after challenge, clinical score for the control group was significantly higher (p < 0.05) than for all three chimeric vaccinated groups. Therefore, intranasal vaccination with CTB-R2-NLKT (SAC102) and R2-NLKT-R2-NLKT (SAC89) chimeric proteins enhanced resistance against intrabronchial challenge with the bacterium as well as stimulating antibody responses to M. haemolytica antigens.