The Research Of Recombinant Subunit Vaccine Against Porcine Contagious Pleuropneumonia

Porcine contagious pleuropneumonia (PCP) is a highly contagious disease which is causedby Actinobacillus pleuropneumoniae (APP) and characterized by severe fibrinous necrotizingand/or hemorrhagic pleuropneumonia in pigs. PCP can cause acute or chronic infection in any ageof pigs, morbidity and mortality of PCP is over 20%, mortality of the acutest type of infectionranges from 80% to 100%, chronic infection is inapparent, which compromised pig growth. Sincethis disease was discovered in 1957, it spread in the worldwide and caused enormous economiclosses in industrialized pig production. Because APP has resistance against many antibiotics,vaccination has been a main measure to prevent PCP. At present, an inactivated whole cell vaccineis mostly applied for PCP prevention and treatment in China. But APP has 15 serotypes, so theprotection efficacy of inactivated vaccines against different serotypes of APPs is unfavorable andthe development of novel vaccine has become a research hotspot. It had been proved that manyattenuated vaccines constructed by molecular biology methods and new ghost vaccine couldprovide effective protection. But along with the declined virulence of attenuated vaccines, theimmunogenicity was also decreased, and moreover, the reversion of virulence might be presented,and ghost vaccine might be inactivated incompletely. Subunit vaccines contain toxic factors hadno those disadvantage and could provide effective protection, but bacteriostasis of subunitvaccines is limited because of no whole bacteria contained, inapparent infected pigs could becarrier without any symptom.In order to research new vaccines, six toxic factors of APP, which were expressed byrecombinant technique, were added into APP7 inactivated vaccine, expected high crossingprotection efficacy against PCP provided by these novel kinds of vaccines.The BALB/C mice were immunized on days of 0, 14 and 28 in following groups:Groupâ… (inactivated vaccine), Groupâ…¡(inactivated vaccine, rApxâ… , rApxâ…¡, rApxâ…¢andrOMP), Groupâ…¢(inactivated vaccine, rApxâ… , rApxâ…¡, rApxâ…¢and rApxâ…£), Groupâ…£(inactivated vaccine, rApxâ… , rApxâ…¡, rApxâ…¢and rApfA) and Control group (PBS), andchallenged with APP1 (5×10⁹cfu) and APP7 (10¹¹cfu) on day 35. After detecting antibody titers,spleen lymphocyte proliferation (SLP), survival rates, lung pathological changes and indirectimmune fluorescence (IIF), the immune protection efficacy of recombinant subunit vaccine wasassessed. Results showed that antibody against OMP of Groupâ… , antibody against Apxâ… andOMP of Groupâ…¡, antibody against ApfA of Groupâ…£, were significantly higher than othergroups (p＜0.05) before challenge. SLP of Groupâ…¡was significantly higher than those of Groupâ… andâ…£(p＜0.01), and than that of Groupâ…¢(p＜0.05) before challenge. Groupâ…¡has the bestsurvival rates, lung pathological changes and indirect immune fluorescence, Groupâ…¢andâ…£were better than Groupâ… . These results indicated that the added recombinant proteins couldimprove crossing protection of inactivated vaccine indeed, antibody against Apxâ… and OMP ofGroupâ…¡was significantly higher than those of other groups, cellular immunity, survival rateagainst APP1 and APP7, lung pathological change and indirect immune fluorescence of Groupâ…¡were markedly superior than the other groups too. It illustrated that recombinant subunit vaccines can provide favorable cross-protection to challenge with different APP serotypes throughactivating and promoting humoral immunity and cellular immunity.