Immune response of rabbits against liposome conjugate of outer membrane protein from Pasteurella multocida serotype 8:A

Abstract

Liposome containing outer membrane protein (OMP) of Pasteurella multocida 8:A was studied on the physicochemical properties, immunogenicity to induce immune response and the in vitro bactericidal effect of immune sera. The particle size of liposome was 3.86, 3.90, 3.99 and 3.42 micro m and the percent protein entrapment of liposime was 83.3, 81.5, 80.5 and 78.6 at week 0, 4, 8 and 12, respectively. The immunogenicity of a vaccine containing P. multocida OMP was investigated. Each group of rabbits was immunized with formalin killed whole cell, liposome OMP, OMP emulsified with Freund's adjuvant, alum OMP and OMP. The ghost liposome and PBS were used as the immunizing a gents for control groups. The results indicated that liposome OMP and OMP freund's adjuvant significantly elicited the highest antibody titers (p<0.05), as shown by ELISA titers a gainst whole cell and OMP of P. multocida. The liposome OMP and OMP emulsified with Freund's adjuvant also significantly produced higher bactericidal activity than other vaccines used (p<0.05). There was correlation between antibody titer against both whole cell and OMP and bactericidal activity of antisera against P. multocida 8:A. The analysis by SDS-PAGE of OMP from Pasteurella multocida 8:A indicated the major band of 37.5 kDa and the minor bands of 23, 27.5, 45 and 97.4 kDa. The same protein bands were observed in both OMP from liposome vaccine and OMP freshly prepared. The study of specificity of rabbit immune sera by western blot showed that all immune sera strongly reacted to major protein band, 37.5 kDa