猪繁殖与呼吸综合征病毒强弱毒株感染对仔猪免疫机能影响的差异

Variance influence of immunity function of piglets infected by the high and the low virulent strains of porcine reproductive and respiratory syndro

20日龄猪繁殖与呼吸综合征(PRRS)阴性健康仔猪滴鼻感染猪繁殖与呼吸综合征病毒(PRRSV)Hn-1/06强毒株和BJ-4弱毒株,于接种后0、5、11、18、30、405、0 d无菌采血,制备血清和分离白细胞,并在感染猪发病死亡或第50天后分别剖杀取各器官组织。经RT-PCR方法检测,强弱毒株在血清、白细胞和各组织器官内分布基本一致;经ELISA方法和免疫荧光抑制试验及IFA流式细胞术检测,强弱毒株感染均诱导机体产生抗N蛋白抗体,强毒株的抗N蛋白抗体产生早于弱毒株;强毒株感染未能诱导产生中和抗体,弱毒株感染后第30天诱导产生了较低水平的中和抗体,随后逐步升高;在整个感染过程中,强毒感染猪CD3+T淋巴细胞及CD4+和CD8+T淋巴细胞亚群均下降,CD4+/CD8+比值远远小于对照组,弱毒感染猪CD3+T淋巴细胞及CD4+和CD8+T淋巴细胞亚群先下降,40 d后逐渐恢复正常水平,CD4+/CD8+比值先下降,11 d后开始逐步上升,18 d后超过对照组,近50 d恢复到正常水平。结果说明,在强毒株感染过程中,细胞免疫被抑制,不能产生有效的体液免疫,导致病毒快速增殖复制;在弱毒株感染过程中,细胞免疫和体液免疫先被抑制,后免疫功能逐步恢复正常水平,使体内病毒进一步被清除。

The PRRS negative healthy piglets of 20 days-old were inoculated by intranasal with the high virulent PRRSV Hwl/06 strain or the low virulent PRRSV BJ-4 strain respectively. At 0,5,11,18,30,40 and 50 d post-in- oculation, the sera and leucocytes were separated aseptically,and the tissues were collected from the died piglets in- fected high virulent strain or the anatomical piglets infected low virulent strain at 50 d post inoculation. The PRRSV in the sera,the leucocytes,and the tissues of the infected piglets was detected by the RT-PCR. The results indicated that the distribution of PRRSV was consistent in all tissues of the piglets infected high virulent and the low virulent strain. The immunity function of the infected piglets was analyzed by ELISA and flow cytometry. The results indicated that the anti-N protein antibody were induced by high virulent and the low virulent strain, and that the anti-N protein antibody of high virulent strain emerged earlier than the low virulent strains. The neutralizing antibody was not produced until high virulent strain infected piglets died,and that the neutralizing antibody was induced at 30 d post-infection by low virulent strain and elevated gradually. In the piglets infected high virulent strain, the CD3^＋ , CD4^＋ ,and CD8^＋ T cells dropped graduallY,and the CD4^＋/CD8^＋ ratio was much smaller than the control group. In the piglets infected low virulent strain, the CD3^＋, the CD4^＋ , and the CD8^＋ T cells decreased, and then increased to normal level at 40 d post-infection（p, i）, and CD4^＋/CD8^＋ ratio decreased before 11 day,and then increased gradually,and exceled control group after 18 day p. i. ,and rebounded to normal level near 50 d p. i. The study results sug- gested that the cellular immunity was suppressed and the effective neutralization antibody could not be induced dur- ing infection of the high virulent strain, and that the cellular immunity and the humoral immunity was both suppressed during infection of the low virulent strains, and then recovered gradually, and viral replication reduced gradually to vanish.