RESUMO
Protective immunity in sheep with bluetongue virus (BTV) infection as well as the role of BTV-induced cytokines during immune response remains unclear. Understanding the basis immunological mechanisms in sheep experimentally infected with serotypes 1 and 8 (BTV-1 and -8) was the aim of this study. A time-course study was carried out in order to evaluate cell-mediated immune response and serum concentrations of cytokines (IL-1ß, TNFα, IL-12, IFNγ, IL-4 and IL-10) with inflammatory and immunological functions. Depletion of T cell subsets (mainly CD4(+), γδ and CD25(+)) together with the absence of cytokines (IFNγ and IL-12) involved in the regulation of cell-mediated antiviral immunity at the first stage of the disease suggested that both BTV-1 and BTV-8 might impair host's capability against primary infections which would favor viral replication and spreading. However, cellular immune response and cytokines elicited an immune response in sheep that efficiently reduced viremia in the final stage of the experiment. Recovery of T cell subsets (CD4(+) and CD25(+)) together with a significant increase of CD8(+) T lymphocytes in both infected groups were observed in parallel with the decrease of viremia. Additionally, the recovery of CD4(+) T lymphocytes together with the significant increase of IL-4 serum levels at the final stage of the experiment might contribute to humoral immune response activation and neutralizing antibodies production against BTV previously described in the course of this experiment. These results suggested that both cellular and humoral immune response may contribute to protective immunity against BTV-1 and BTV-8 in sheep. The possible role played by IL-10 and CD25(+) cells in controlling inflammatory and immune response in the final stage of the experiment has also been suggested.