Studies On Immunological Characteristics Of Attenuated And Killed Vaccine Based On Highly Pathogenic Prrs

Porcine reproductive and respiratory syndrome (PRRS) was caused by porcine reproductive and respiratory syndrome virus (PRRSV), as it was first described in North America in 1987, PRRS had became one of the most economically important disease in swine industry worldwide. In 2006, a highly pathogenic PRRS (HP-PRRS) appeared in pigs in China, this disease spread quickly, was characterized by a prolonged fever, anorexia, red coloration of ears and body, diarrhea, associated with high morbidity and mortality, resulting in huge economic losses in pig industry of China. Later a highly pathogenic porcine reproductive and respiratory syndrome virus (HP-PRRSV) had been confirmed to be the main pathogen of HP-PRRS. To effectively prevent and control HP-PRRS, our country had focused on the researches on vaccines against PRRS. Currently, there were attenuated and killed vaccine to be used to the clinical, in this study, we studied the immunological characteristics induced by attenuated and killed vaccine based on HP-PRRSV, established a basis for further studying the immune mechanisms and immunological characteristics of vaccines based on HP-PRRSV, and provided experiment data for better preventing and controlling HP-PRRS.In this study, we studied immunological characteristics induced by HP-PRRS (HuN4) attenuated vaccine and HP-PRRS (JXA1) killed vaccine respectively, twenty-five 4 to 5-week-old healthy weaned piglets, PRRSV antigen and antibody free, were randomly assigned to three groups. Group 1(n=5) pigs were served as unimmunized controls, group 2 (n=10) pigs were immunized with HP-PRRS (HuN4) attenuated vaccine, group 3 (n=10) pigs were immunized with HP-PRRS (JXA1) killed vaccine, and all groups were challenged with HuN4 highly virulent strain on 21 day post vaccination (DPV). Pigs were slaughtered and taken blood samples at various points following vaccination or challenge, rectal temperatures and clinical signs were recorded every day, blood samples were collected for detecting viremia and the dynamic distribution of PRRSV in piglets by fluorogenetic quantitative RT-PCR, the PRRSV-special antibody and TNF-α, IFN-α, IL-1, IL-6, CRP in serum were detected by ELISA, tissue samples from main tissues were collected for histopathological testing.The results indicated that in group 2, PRRSV-special antibody could be detected on 14 dpv, viremia were cleared completely on 21 day post challenge (DPC), no obvious lesions were detected in most tissues throughout the vaccination periods, pigs developed mild clinical symptom and mild lesions in most tissues after challenge, in group 3, PRRSV-special antibody could not be detected throughout the vaccination periods, viremia existed in serum persistently after challenge, most tissues had mild lesions post vaccination, lesions in most tissues and the clinical symptom in group 3 were more serious than in group 2, but obviously milder than in group 1; In group 2, the replication of PRRSV was obviously inhibited in pigs after challenge, in group 3, the replication of PRRSV in pigs was similar but milder than in control group, and could be inhibited after challenge; all cytokine levels decreased in serum in group 2 and group 3 during the vaccination periods, indicated that immunization by PRRS vaccine might inhibite innate immune responses slightly. But all cytokine levels increased in serum in group 2 and group 3 after challenge, indicated that immunization by PRRS vaccine may elicite adaptive immune responses mainly, and piglets immunized with HuN4 atttenuated vaccine could develop more effective humoral response. Our studies showed that piglets immunized with HuN4 atttenuated vaccine could develop a rapid and effective humoral response, the clinical symptom of HuN4 atttenuated vaccine was obviously milder than JXA1 killed vaccine against HuN4 highly virulent strain.