Characterization of Antigenic Determinants in ApxIIA Exotoxin Capable of Inducing Protective Immunity to Actinobacillus pleuropneumoniae Challenge

Abstract

Actinobacillus pleuropneumoniae is the causative agent of porcine pleuropneumonia. Among the virulence factors of the pathogen, ApxIIA, a bacterial exotoxin, is expressed by many serotypes and presents a plausible target for vaccine development. We characterized the region within ApxIIA that induces a protective immune response against bacterial infection using mouse challenge model. Recombinant proteins spanning the length of ApxIIA were produced and antiserum to the full-length ApxIIA was induced in mice. This antiserum recognized fragments #2, #3 and #5 with high binding specificity, but showed poor recognition for fragments #1 and #4. Of the antisera induced in mice by injection of each fragments, only the antiserum to fragment #4 failed to efficiently recognize the full-length antigen, although the individual antisera recognized their cognate antigens with almost equal efficiency. The protective potency of the immunogenic proteins against a challenge injection of bacteria in vivo correlated well with the antibody titer. Fragment #5 induced the highest level of protective activity, comparable to that by the full-length protein. These results support the use of fragment #5 to produce a vaccine against A. pleuropneumoniae challenge, since the small antigen peptide is easier to handle than is the full-length protein and can be expressed efficiently in heterologous expression systems.

• Actinobacillus pleuropneumoniae
• Epitope
• Immune response
• Vaccine

ACKNOWLEDGMENT

This work was supported by a grant from the BioGreen 21 Program (No. PJ007044), Rural Development Administration, Republic of Korea. Dr. Y.-S. Jang was supported by research fund of Chonbuk National University in 2010. We would like to express our sincere thanks to the Center for University-Wide Research Facilities of the Chonbuk National University for providing the facility for this study.

Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.