An attenuated EIAV vaccine strain induces significantly different immune responses from its pathogenic parental strain although with similar in vivo replication pattern.

The EIAV (equine infectious anemia virus) multi-species attenuated vaccine EIAV(DLV121) successfully prevented the spread of equine infectious anemia (EIA) in China in the 1970s and provided an excellent model for the study of protective immunity to lentiviruses. In this study, we compared immune responses induced by EIAV(DLV121) to immunity elicited by the virulent EIAV(LN40) strain and correlated immune responses to protection from infection. Horses were randomly grouped and inoculated with either EIAV(DLV121) (Vaccinees, Vac) or a sublethal dose of EIAV(LN40) (asymptomatic carriers, Car). Car horses became EIAV(LN40) carriers without disease symptoms. Two of the four Vac horses were protected against infection and the other two had delayed onset or reduced severity of EIA with a lethal EIAV(LN40) challenge 5.5 months post initial inoculation. In contrast, all three Car animals developed acute EIA and two succumbed to death. Specific humoral and cellular immune responses in both Vac and Car groups were evaluated for potential correlations with protection. These analyses revealed that although plasma viral loads remained between 10(3) and 10(5)copies/ml for both groups before EIAV(LN40) challenge, Vac-treated animals developed significantly higher levels of conformational dependent, Env-specific antibody, neutralizing antibody as well as significantly elevated CD4(+) T cell proliferation and IFN-γ-secreting CD8(+) T cells than those observed in EIAV(LN40) asymptomatic carriers. Further analysis of protected and unprotected cases in vaccinated horses identified that cellular response parameters and the reciprocal anti-p26-specific antibody titers closely correlated with protection against infection with the pathogenic EIAV(LN40). These data provide a better understanding of protective immunity to lentiviruses.

[Development of a CFSE-based flow cytometry for evaluating EIAV-stimulated proliferation of T lymphocytes].

AIM: To develop a flow cytometry using (5-carboxyfluorescein diacetate succinmidyl ester, CFSE) to detect the proliferation of specific T lymphocytes from equine infectious anemia virus (EIAV). METHODS: Peripheral blood mononuclear cells (PBMC) were isolated, stained with CFSE and incubated with EIAV for 5 days. After interacted with either CD4(+) or CD8(+) antibody, the cells were detected for proliferated population, which contained serially 2-fold reduced CFSE in CD4(+) and CD8(+) T lymphocytes. RESULTS: The concentration of CFSE, and the type, concentration and reaction time of EIAV-specific antigens were tested and optimized to improve the sensitivity and specificity of this flow cytometry-based assay. PBMCs isolated from the horses infected with either virulent or vaccine strains of EIAV and health controls were analyzed to evaluate this technique. The proliferation rates of CD4(+) and CD8(+) T lymphocytes were observed in the cells from differently treated horses. CONCLUSION: The CFSE-based flow cytometry is a reliable tool to analyze antigen-specific proliferation of lymphocytes, which plays an important role in evaluating the immune responses induced by EIAV and other viruses.

[A flow cytometric assay for the expression of interferon gamma in T lymphocytes and its application in the study of EIAV-induced immune response].

OBJECTIVE: The attenuated vaccine of equine infectious anemia virus (EIAV) is the first lentiviral vaccine that provides solid protection against the infection of EIAV virulent strains. Study of the immune response induced by EIAV vaccine is an important approach to understand the immunity to other lentiviruses. IFN-gamma expressed by specifically stimulated lymphocytes is an important indicator for the evaluation of T cell-mediated immunity. A flow cytometry based assay was established in this study to accurately and effectively detect IFN-gamma expression in different subtypes of T lymphocytes in EIAV-infected horses. METHODS: Peripheral blood mononuclear cells (PBMC) were prepared from horses inoculated with EIAV vaccine stain FDDV (fetal donkey dermal-attenuated virus vaccine), virulent strain LV or saline (health control), were stimulated in vitro with FDDV or PMA + Inomycin. Brefeldin A was added into the cell culture to block protein secretions. Stimulated cells were then labeled with monoclonal antibodies specific for equine CD4 and CD8 surface markers, as well as an IFN-gammaspecific monoclonal antibody. Flow cytometry was applied to detect CD4+ and CD8+ lymphocytes expressing IFN-gamma. RESULTS: IFN-gamma positive cell population isolated from FDDV-immunized horses was 1.7 +/- 0.9% in CD4+ T cells and 6.1 +/- 1.2% in CD8+ T cells (n=4). In contrast, only 0.6 +/- 0.1% of IFN-gamma positive cells in CD4+ subset and 2.4 +/- 0.9% of IFN-gamma positive cells in CD8+ subset of T cells were detected for PBMC isolated from LV-infected horses (n=4). CONCLUSION: The multi-fluorescence cell flowmetry detecting both the IFN-gamma expressing cells and subsets of T lymphocytes simultaneously, is specific, stable and reproducible in evaluating antigen-specific response of IFN-gamma-producing lymphocytes. This is an essential approach to study the protective immunity induced by EIAV vaccine.