Escherichia coli -derived outer membrane vesicles deliver galactose-1-phosphate uridyltransferase and yield partial protection against Actinobacillus pleuropneumoniae in mice.

In our previous studies, we have identified several in vivo -induced antigens and evaluated their potential as subunit vaccine candidates in a murine model, in which the recombinant protein GalT showed the most potent immunogenicity and immunoprotective efficacy against Actinobacillus pleuropneumoniae . To exploit a more efficient way of delivering GalT proteins, in this study, we employed the widely studied E. coli outer membrane vesicles (OMVs) as a platform to deliver GalT protein and performed the vaccine trial using the recombinant GalT-OMVs in murine model. Results revealed that GalT-OMVs could elicit highly specific IgG antibody titer that was comparable with adjuvant GalT group. Significantly higher lymphocyte proliferation and cytokines secretion level were observed in GalT-OMVs group. 87.5% and 50% of mice were protected from lethal dose challenge of A.pleuropneumoniae in active or passive immunization, respectively. Histopathologic and immunohistochemical analysis showed remarkably reduced pathological changes and infiltration of neutrophils in the lungs of mice immunized with GalT-OMVs after challenge. Taken together, these findings confirm that OMVs can be used as a platform to deliver GalT protein and enhance its immunogenicity to induce both humoral and cellular immune responses in mice.