Evaluation Of The Immunoprotective Efficacy Of Subunit Vaccine Candidates Of Haemophilus Parasuis Serovar 5

Haemophilus parasuis(H. parasuis) is a conditioned pathogen of swine upper respiratory tract, and able to cause severe systemic disease, called Haemophilus parasuis disease or Gl?sser ’ s disease, pathologically characterized by arthritis, pneumonia, serositis and meningitis. It’s one of the most severe bacterial infectious diseases and causes great economic losses to world pig industry.Based on agar diffusion test and indirect hemagglutination test, H. parasuis can be divided into at least 15 serovars, but about 20% of the strains cannot be typed. Currently, there are no commercially available vaccine confers effective immune protection to all serovars of H. parasuis infection. Some of the secretory proteins and outer membrane proteins are supposed to be effective protective antigens and have the potential as candidate antigens to develop effective vaccines. Currently, 7 secretory proteins(CdtB, CdtC, AfuA, HbpA, OppA, HktE, HPS-04307) of H. parasuis serovar 5 Nagasaki reference strain have been screened by proteomic technology in our laboratory. To evaluate the potential of these 7 proteins to develop recombinant subunit vaccine, the cdtB and cdtC were cloned(the recombinant plasmids of other 5 proteins have been completed in our laboratory), expressed and purified as His fusion proteins in this study. Initially, the mice were immuned with individual proteins and challenged with H. parasuis. 5 fusion proteins rCdtB, rCdtC, rAfuA, rOppA, rHPS-04307 out of these 7 secretory proteins were found to be protective. We further evaluated the immunoprotective efficacy of the mixed proteins in a mouse model of H. parasuis infection. All 7 proteins elicited humoral antibody responses and conferred different levels of protection against challenge with a lethal dose of H. parasuis serovar 5 HN10 strain and serovar 13 ZD12 strain in mouse models. The mixed proteins conferred highest protection rate to mice(The protection rate to mice against a lethal dose of H. parasuis serovar 5 HN10 strain and serovar 13 ZD12 strain infection was 85% and 60%, respectively). In addition, results of whole blood killing bacteria assay demonstrated that the antisera against the 7 individual proteins efficiently inhibited H. parasuis growth. Each individual proteins efficiently stimulated T lymphocyte proliferation in mice in a lymphocyte proliferation test. Our results indicated that rCdtB, rCdtC, rAfuA, rOppA, rHPS-04307 induced effective protection against a lethal dose of H. parasuis serovar 5 HN10 strain and serovar 13 ZD12 strain infection, which may facilitate the development of a new generation of multi-component vaccine.