Immunological Identification and Characterization of Extracellular Serine Protease-Like Protein Encoded in a Putative espP2 Gene of Haemophilus parasuis

抄録

Haemophius parasuis is known to produce a group of virulence-associated autotransporter (AT) proteins, VtaAs; however, no other ATs have been characterized yet. On the basis of reported sequence of a putative espP2 gene for extracellular serine protease (ESP)-like protein of H. parasuis, this putative AT gene was successfully amplified from H. parasuis serotype 5 field strain HPS0819, cloned and sequenced. The confirmed ORF sequence showed 100% identity with the reported putative espP2 gene. The recombinant ESP-like protein purified from Escherichia coli with pET expression system was used for immunological characterization. An approximately 85 kDa antigen was detected in cultured H. parasuis by using antiserum to the purified ESP-like protein and antibodies against the recombinant ESP-like protein was detected in a selected serum from pigs with experimental H. parasuis infection. The results indicated that H. parasuis could produce ESP-like protein in vitro and in vivo. In an immune protection study using guinea pigs, 6 out of 10 animals immunized with the recombinant ESP-like protein survived after challenge with 5×10⁹ bacteria of strain HPS0819 whereas 7 out of 10 animals immunized with formalin-inactivated H0819 bacterin survived after challenge. The results suggest that ESP-like protein could be one of vaccine antigen candidates for H. parasuis infection.