Cloning, expression and characterization of a cell wall surface protein, 6-phosphogluconate dehydrogenase, of Haemophilus parasuis.

Haemophilus parasuis (H. parasuis) is a swine pathogen responsible for the Glässer's disease. In order to understand the pathogenesis of the H. parasuis infection, the gnd gene encoding a cell surface protein, 6-phosphogluconate-dehydrogenase (6PGD) of H. parasuis was inducibly expressed in Escherichia coli BL21 with a hexahistidyl N-terminus to permit its purification. Western blotting using the r6PGD-specific antiserum showed that the 6PGD protein is on the cell surface of H. parasuis. The characterization of 6PGD in H. parasuis pathogenesis involved as an adhesion and its immunogenicity in mice was further investigated. The adherence assay with H. parasuis and swine alveolar epithelial cells (SJPLC) pre-incubated with (His)(6)6PGD and non-incubated SJPLC showed a noticeable reduction in the adhesion of H. parasuis in the (His)(6)6PGD pre-incubated SJPLC compared to the non-incubated SJPLC. Further, the r6PGD protein induces the production of IL-8 and IL-6 by SJPLC. Furthermore, immunization with the r6PGD protein can provide the protective efficacy by 75% following intraperitoneal administration of a 5×LD(50) dose of H. parasuis SH0165, and elicited a good protective immune response, which demonstrated the importance of 6PGD to bacterial pathogenesis. Identification and characterization of the role of H. parasuis 6PGD in adhesion and immunogenicity will allow us to use this protein to develop new antimicrobial therapies and/or vaccines.