Haemorrhagic septicaemia: correlation of vaccinal antibody responses in mice with protection against Pasteurella multocida strain M1404.

This study examined the protection induced by oil adjuvant vaccine and broth bacterin in mice. Protective immunity was induced by both oil adjuvant and bacterin vaccination procedures. Oil adjuvant vaccination induced a 10(5)-fold increase for lethal challenge over control mice, while secondary vaccination induced a further 10-fold increase in resistance to lethal challenge. Broth bacterin induced a slightly weaker protective response with 10(4)- and 10(5)-fold increases in resistance to lethal challenge following primary and secondary vaccination, respectively. There was a significant relationship between IgG antibody levels and resistance to challenge (P = 0.026). Protection lasted for at least 20 weeks after a primary oil adjuvant vaccination. There was also a strong and significant relationship between IgG antibody levels and the passive protection afforded by serum transfer in each experiment within this study and the overall correlation was highly significant (P = 0.00001). There appeared to be a relationship between protection and the antibody response to major protein bands with the apparent molecular mass Mr. 94,000; 80,000; 67,000; 35,000 and 32,000 as well as to the bands in the region of the lipopolysaccharide components of P. multocida (approximately Mr, 14-15,000). Whether protection resulted from recognition of specific antigens or was a result of both antibody levels and antibody specificity remains to be defined.