Abstract
Although swine are natural hosts for influenza A viruses, the porcine T-cell response to swine influenza A virus (FLUAVsw) infection has been poorly characterized so far. We have studied Ki-67 expression and FLUAVsw-specific production of IFN-γ, TNF-α and IL-2 in CD4(+) and CD8β(+) T cells isolated from piglets that had been intratracheally infected with a H1N2 FLUAVsw isolate. IFN-γ(+)TNF-α(+)IL-2(+) multifunctional CD4(+) T cells were present in the blood of all infected animals at one or two weeks after primary infection and their frequency increased in four out of six animals after homologous secondary infection. These cells produced higher amounts of IFN-γ, TNF-α and IL-2 than did CD4(+) T cells that only produced a single cytokine. The vast majority of cytokine-producing CD4(+) T cells expressed CD8α, a marker associated with activation and memory formation in porcine CD4(+) T cells. Analysis of CD27 expression suggested that FLUAVsw-specific CD4(+) T cells included both central memory and effector memory populations. Three out of six animals showed a strong increase of Ki-67(+)perforin(+) CD8β(+) T cells in blood one week post infection. Blood-derived FLUAVsw-specific CD8β(+) T cells could be identified after an in vitro expansion phase and were multifunctional in terms of CD107a expression and co-production of IFN-γ and TNF-α. These data show that multifunctional T cells are generated in response to FLUAVsw infection of pigs, supporting the idea that T cells contribute to the efficient control of infection.