免疫抑制对EIAV弱毒疫苗免疫马体内疫苗弱毒株载量的影响

The Plasma Load of Inoculated EIAV Vaccine Strain EIAV_(FDDV) Was Not Boosted by Immune Suppression

为了研究马传染性贫血弱毒疫苗EIAVFDDV在体内的生物学特性,特别是在免疫马血浆中低拷贝存在状态的形成原因,使用连续给予地塞米松的方法,对EIAVFDDV免疫马匹进行了免疫功能抑制.连续给药10天后,以植物血凝素(PHA)作为刺激原的淋巴细胞非特异性增殖实验表明,实验马匹的免疫系统功能受到了明显抑制.使用实时RT-PCR对免疫抑制前后实验马匹体内EIAVFDDV的载量进行了定量检测.结果显示,EIAVFDDV免疫马匹体内的病毒载量在2匹马中未见升高,1匹马体内略有增高,但仍处于EIAVFDDV在免疫马匹体内载量的正常范围.作为对照,强毒株隐性携带马的病毒载量提高了约25000倍,并出现了典型的临床症状.实验结果提示,致弱后病毒特有的生物学特性,而非免疫压力,是EIAV疫苗株在宿主血浆中低拷贝存在的主要原因.同时,在免疫系统功能受抑制状态下,疫苗株在免疫马体内仍然表现出了相对稳定的低拷贝复制状态,进一步显示了EIAVFDDV在应用中的安全性.

The attenuated Chinese equine infectious anemia virus （EIAV） vaccine is the first lentiviral vaccine that provides solid protective immunities to vaccinated horses. To investigate properties of EIAV vaccine, especially the relationship between its replication and the immunity, viral plasma loads of an EIAV vaccine strain EIAVFDDV in immune suppressed horses were detected. Three horses, which were immunized with EIAVFDDV for 16 months, were treated with dexamethasone for 14 days to suppress their immunities. Reduced immune response in these animals was confirmed by significantly declined lymphocyte proliferation rate detected after 10 days of the drug treatment. The plasma viral loads of EIAVFDDV, which was indicated by the genomic RNA copy numbers, in horses before and after the treatment of dexamethasone were monitored by real time RT-PCR. Results revealed that the viral plasma loads in two of three immune-suppressed horses were kept a steady low level around 10^3 -10^4 copies/ml. The load was increased by 10 folds in the third horse, but was still among the standard levels for EIAVFDDV vaccinated horses. As a positive control, the viral copy number of an asymptomatic carrier of EIAV virulent strain EIAVLiao was jumped nearly 25 000-fold higher after being treated with dexamethasone. The typical clinical symptoms of EIA, characterized by febrile episodes and thrombocytopenia, were also appeared in this horse. These results clearly indicate that it is the unique biological feature of the attenuated EIAV vaccine, but not the immunity, resulted in EIAVFDDV remaining in low levels in the body harmlessly. In addition, the steady low level of viremia and the inability to cause clinical symptoms of EIAVFDDV in immune-suppressed hosts further demonstrated the safety of attenuated Chinese EIAV vaccines. The data provide a new sight for studies on the immunity to lentiviruses.