Martelli Paolo, Cordioli Paolo, Alborali Loris Giovanni, Gozio Stefano, De Angelis Elena, Ferrari Luca, Lombardi Guerino, Borghetti Paolo
Department of Animal Health, University of Parma, Via del Taglio, 8, 43100 Parma, Italy.
Vaccine. 2007 Apr 30;25(17):3400-8. doi: 10.1016/j.vaccine.2006.12.050. Epub 2007 Jan 5.
The purpose of this study was to assess the immune response in pigs intradermally vaccinated with a commercially available attenuated porcine reproductive and respiratory virus (PRRSV) vaccine (Porcilis PRRS) and subsequently exposed to a heterologous (Italian cluster) field strain of virulent PRRSV. A total of 18, 4-week-old pigs seronegative for PRRSV were allocated to 1 of 3 groups (groups A, B, and C). At 5 weeks of age, pigs of groups A (n=6 pigs) and B (n=6 pigs) were vaccinated intramuscularly and intradermally, respectively, with Porcilis PRRS. The more conventional intramuscular route of vaccination was included for comparative purposes with the intradermal route of vaccination (performed with the I.D.A.L. vaccinator). Pigs of group C (n=6 pigs) were kept as nonvaccinated controls. At post-vaccination (PV) days 7, 14, 21, 28, and 35, blood samples were collected for detection of vaccine virus (PCR) and antibodies (ELISA), and for changes in PBMC (flow cytometry). At PV day 35, pigs of all groups were each exposed (challenged) intranasally to a heterologous field strain (78% ORF5 sequence homology between vaccine and field virus) belonging to the Italian cluster of the European genotype of PRRSV. At post-challenge (PC) days 0, 3, 7, 10, 13, and 17, blood samples were collected for detection and quantitation of virus and antibodies, and for changes in PBMC as described above for blood samples collected PV. Throughout the experiment all pigs were observed daily for clinical signs. At PC days 7 and 17, two pigs and four pigs, respectively, of each group were euthanized and examined for macroscopic lesions. Following vaccination some pigs of groups A and B had a detectable viremia that in two pigs (one pig of group A and one pig of group B) lasted until PV day 28. However, all pigs (groups A, B, and C) remained clinically normal. All vaccinated pigs developed a serological response (ELISA) to PRRSV. Presumptive evidence for vaccine-induced protective immunity against the heterologous challenge strain was provided by finding that viremia following challenge was generally less (incidence) and significantly less (titers) in vaccinated pigs than in nonvaccinated pigs. No differences were apparent between pigs vaccinated intramuscularly and those vaccinated intradermally. The absence of virulent-virus-induced clinical signs and macroscopic lesions in nonvaccinated as well as in vaccinated pigs precluded a more definitive evaluation of the magnitude of protective immunity provided by vaccination or by the route of vaccination. Some likely treatment-associated changes in lymphocyte subpopulations were observed among the three treatment groups. These changes and their potential relationship to protective immunity are discussed.
本研究的目的是评估用市售减毒猪繁殖与呼吸综合征病毒（PRRSV）疫苗（Porcilis PRRS）皮内接种猪，随后暴露于异源（意大利毒株群）强毒PRRSV田间毒株后的免疫反应。总共18头4周龄PRRSV血清阴性的猪被分配到3组中的1组（A组、B组和C组）。5周龄时，A组（n = 6头猪）和B组（n = 6头猪）的猪分别通过肌肉注射和皮内注射接种Porcilis PRRS。纳入更传统的肌肉注射接种途径是为了与皮内接种途径（使用I.D.A.L.接种器进行）作比较。C组（n = 6头猪）的猪作为未接种疫苗的对照。在接种疫苗后（PV）第7、14、21、28和35天，采集血样用于检测疫苗病毒（PCR）和抗体（ELISA），以及检测外周血单核细胞的变化（流式细胞术）。在PV第35天，所有组的猪均经鼻暴露（攻毒）于属于欧洲基因型PRRSV意大利毒株群的异源田间毒株（疫苗与田间病毒之间的ORF5序列同源性为78%）。在攻毒后（PC）第0、3、7、10、13和17天，采集血样用于检测和定量病毒及抗体，以及检测外周血单核细胞的变化，方法同接种疫苗后采集的血样。在整个实验过程中，每天观察所有猪的临床症状。在PC第7天和17天，每组分别对2头猪和4头猪实施安乐死并检查肉眼可见病变。接种疫苗后，A组和B组的一些猪出现了可检测到的病毒血症，其中2头猪（A组1头猪和B组1头猪）的病毒血症持续到PV第28天。然而，所有猪（A组、B组和C组）临床均正常。所有接种疫苗的猪均对PRRSV产生了血清学反应（ELISA）。通过发现攻毒后的病毒血症在接种疫苗的猪中通常比未接种疫苗的猪少（发生率）且显著少（滴度），提供了疫苗诱导的针对异源攻毒株的保护性免疫的推定证据。肌肉注射接种的猪和皮内注射接种的猪之间没有明显差异。未接种疫苗的猪和接种疫苗的猪均未出现强毒病毒诱导的临床症状和肉眼可见病变，这妨碍了对疫苗接种或接种途径所提供的保护性免疫程度进行更明确的评估。在三个治疗组中观察到了一些可能与治疗相关的淋巴细胞亚群变化。讨论了这些变化及其与保护性免疫的潜在关系。
