Immunogenicity of highly conserved recombinant VacJ outer membrane lipoprotein of Pasteurella multocida

Bacterial lipoproteins are emerging targets for inducing protective immunity against many infectious diseases. VacJ is a highly conserved and widely distributed outer membrane lipoprotein of Pasteurella multocida strains, which are known to affect a wide range of domestic as well as wild animals and birds. In the present study, the gene encoding for mature VacJ outer membrane lipoprotein of P. multocida serogroup B:2 strain P52 was cloned and over-expressed in Escherichia coli as a fusion protein. The purified recombinant VacJ protein (∼44 kDa) was used for immunizing mice (6/group) along with adjuvants (FCA and alum) in two experiments. Immunization of mice with rVacJ (30 μg and 75 μg/mice) elicited humoral immune response with significant (P < 0.01) rise in antigen-specific titers of IgG and its subtypes (IgG1 and IgG2a). No protection was noticed in mice immunized with rVacJ (30 μg) along with FCA followed by challenge with 100 LD50 of the homologous strain. On the contrary, higher rVacJ dose (75 μg) along with FCA and alum provided 66.7% and 50% protection respectively, at reduced challenge dose (8 LD50). The study indicated that a lipidated recombinant VacJ lipoprotein with suitable adjuvants could potentially act as candidate antigen for vaccine development against pasteurellosis in livestock.