怀孕后期感染PRRS病毒母猪所产新生仔猪的免疫反应

将PRRS病毒BJ－4株感染怀孕后期（约90天）的抗体阴性和阳性母猪，待自然分娩后，观察新生仔猪的免疫应答。结果显示，接种PRRS病毒BJ－4的母猪没有表现出明显的临床症状，没有出现流产死产。新生仔猪浦被子前血清中PRRS病毒核酸TR－PCR检测和ELISA抗体阴性，哺乳后特异性抗体出现，5－6周母源抗体逐渐下降；20日龄猪瘟疫苗免疫后疫苗抗体维持时间短，仔猪在40日龄后进入野毒感染的危险期。RT－nested PCR检测血清中PRRS病毒核酸和易感仔猪病毒特异性抗体监测的结果提示仔猪群内可能存在水平传播。流式细胞术检测外周血淋巴细胞亚群发现CD3^ 细胞减少，CD4^ 细胞显著下降，CD8^ ，CD4^ CD8^ 和SLA－DR^ 表达细胞升高。以上结果表明在感染后病毒能够长期持续性存在，猪场内新生仔猪母源抗体逐渐下降后，通过水平传播受到感染，感染后免疫应答受到不利影响。

Immune Responses of Newborn Piglets from Sows Infected with Porcine Reproductive and Respiratory Syndrome Virus at Late-Pregnancy

The late_pregnant sows (about 90 days)were inoculated porcine reproductive and respiratory syndrome virus BJ_4 strain to observe effects of infection on immune responses of newborn piglets under normal environments instead of experimental conditions.No specific antibody and virus could be detected in serum of newborn piglets,but specific antibody appeared after sucking colostrums.It was about 6 weeks later when the maternal antibody declined.Results also showed antibodies against hog cholera vaccine in newborn piglets from infected sows had shortened time of persistence compared with controls when vaccinated at 20_day_old.Piglets may be infected by field strain at 40_day_old detection of ORF_7 gene in serum of piglets from sows infected BJ_4 strain by RT_nested PCR and specific antibody turned out in serum of sentinel piglets indicated the existence of PRRSV horizontal transmisson.The percentage of CD3 and CD4 cells in peripheral bloods was decreased while that of CD8 ,CD4 CD8 ,SLA_DR was increased after PRRSV infection.All these suggested newborn piglets may be infected once maternal antibody declined ,which lead to infected piglets may have lower level of immune response to other pathogens or vaccines.