Acute toxicity and immunoprotection of recombinant apxI toxin of Actinobacillus pleuropneumoniae in mice / 生物工程学报

Acute toxicity and immunoprotection of Actinobacillus pleuropneumoniae (APP) ApxI toxin recombinant proteins (include crude inclusion bodies and refolded recombinant protein) were evaluated in mice, and compared with the natural ApxI extracted from culture supernatant of APP serotype 10. In the acute toxicity experiment, the three proteins were intraperitoneally injected into Kunming mice in a dose of 200microg per mouse. The body and organ weight, heamatological and biochemical indexes were examined at 24h, 7 days and 14 days post administration. There was no death after the intraperitoneal administration of the three proteins, and no significant change was found in the body weight, organ indexes, heamatological and biochemical indexes. To study their immunoprotection, the three proteins were emulsified with Freund's adjuvant respectively and vaccinated the mice twice with a 2-week of interval. Two weeks after the second vaccination, the mice were challenged intraperitoneally with a lethal dose of APP serotype 10 (1.09 x 10(8) cfu), and serums were examined by an ApxI-specific ELISA. The results revealed that the recombinant protein had a good immunogenicity and could induce protection immune reaction.

Cloning and expression of the Apx IVA gene of Actionbacillus pleuroneumoniae and development of an indirect ApxIVA-ELISA / 生物工程学报

Apx IV, a forth RTX toxin indentified in Actionbacillus pleuropneumoniae recently, is expressed by all A. pleuropneumoniae regardless the serotypes and inducible only in vivo toxin, so it is the optimal to develop species-specific and differentiated diagnostic assay. Here the 2445bp DNA fragment of apxIVA gene of A. pleuroneumoniae was amplified and fused in-frame to the downstream of the T7 promoter and 6 His Tag of the prokaryotic expression vector pET-28b. The construct was transformed into E. coli BL21(DE3). After induction by 1.0 mol/L IPTG, a recombinant protein about 90 kD in size, designed as ApxIVAN, was detected, which was present as inclusion bodies and reacted specifically with swine antisera to the APP-serotype-1 by dot-blot. An indirect ELISA (ApxIVA-ELISA) was developed using purified recombinant ApxIVAN from the inclusion bodies as described previously, which had excellent specificity to A. pleuroneunoniae. Using the ApxIVA-ELISA, the ApxIV antibodies were not detected in the inactivated APP bacterins vaccinated pigs, but were detected in A. pleuropneumoniae serotype 1, 2 and 7 infected pigs and mice. These results suggested that ApxIVA-ELISA can be used not only to detect all serotypes of APP, but also to differentiate the naturally infected and inactivated vaccine immunized pigs.