[The difference in specific humoral immune responses induced with the attenuated equine infectious anemia vaccine strain and virulent strain.].

Abstract: To disclose the potential roles of humoral immune response in the EIAV vaccine-induced protective immunity. In this study, major parameters of humoral immunity be compared between horses inoculated with the EIAV vaccine strain and the pathogenic virulent strain. Methods: Experimental horses were randomly assigned into the group inoculated with the vaccine strain EIAV(DLV); (the vaccinated group) and the group inoculated with sub-morbigenous dose of virulent strain EIAV(Liao); (the inapparent infection group). Humoral immunity parameters, including binding endpoint titer and avidity index of antibodies to the envelop protein (Env) and the capsid protein (P26), and the conformation-dependent index of the Env antibody, were assayed and compared between these two groups by using ELISA. Neutralizing antibodies to the EIAV vaccine strain and a pathogenic strain were simultaneously detected by using plaque forming unite assay (PFU) and reverse transcriptase activity assay, respectively. Results: In general, all humoral parameters increased with a time-dependent manner in both the vaccinated and the inapparent infection group. However, significantly higher antibody activities for P26 binding endpoint titer and Env avidity index were detected in the vaccinated group within 2 months post infection (P<0.05). Furthermore, the conformation-dependent index of the Env antibody in the vaccinated group was significantly higher than that in the inapparent infection group throughout the entire observation period (P<0.05). The most dramatic difference between these experimental groups was in the raise of the neutralizing antibody. The antibody neutralizing both the vaccine strain EIAV(DLV); and a virulent strain EIAV(DLV34); was detected significantly earlier and in higher titers in vaccinated horses than in virulent strain-infected horses (P<0.01 for EIAV(FDDV); and P<0.05 for EIAV(DLV34);). Conclusions: Statistically significant differences in EIAV-specific binding antibodies and the neutralizing antibody are detected between animals induced with the EIAV vaccine strain and the virulent strain. Importantly, the significantly early and strong responses in the neutralizing antibody and the conformation-dependent Env antibody induced by the vaccine implicate special roles these antibodies playing in EIAV vaccine-induced immune protection.