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Correlation between the induction of Th1 cytokines by an attenuated equine infectious anemia virus vaccine and protection against disease progression
Abstract
The equine infectious anemia virus (EIAV) donkey-leukocyte attenuated vaccine (DLV) has been used to protect against equine infectious anaemia (EIA) disease for several decades in China. The attenuated mechanism and immunological protective mechanisms remain to be elucidated. To identify responses that correlate with the protection against disease, we immunized horses with DLV, followed by challenge with an EIAV wild-type strain LN. All vaccinated horses were asymptomatic and had a low level of virus replication (<10 copies ml−1). The expression level of cytokines including gamma interferon, interleukin 2 and 12 in DLV immunized horses was 5–100-fold higher than that in non-vaccinated controls (n=4, P<0.01). After challenge with virulent LN, horses vaccinated with DLV showed lower viral loads (<103 copies ml−1) with no temperature increase, except for one transient febrile episode in one animal. In contrast, horses in the non-vaccinated control group experienced much higher viral loads (>107 copies ml−1) and intermittent febrile episodes. Cytokine production in the DLV-vaccinated horses increased and attained a plateau level at approximately 50 days post-vaccination, and exceeded 107 copies per 107 peripheral blood mononuclear cells (PBMCs) 1–3 months post-challenge. However, non-vaccinated control horses died after several fever episodes (⩾39 °C), which coincided with higher viral load (106–107 copies ml−1) and lower cytokine production (<104 copies per 107 PBMCs). The results indicate that high levels of EIAV-specific cytokines induced by the attenuated EIAV vaccine may contribute to the protective immune response against EIA disease.
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