Rapid and Transient Activation of gd T Cells to IFN-g Production, NK Cell-Like Killing, and Antigen Processing during Acute Virus Infection

gd T cells are the majority peripheral blood T cells in young cattle. The role of gd T cells in innate responses against infection with foot-and-mouth disease virus was analyzed on consecutive 5 d following infection. Before infection, bovine WC1 gd T cells expressed a nonactivated phenotype relative to CD62L, CD45RO, and CD25 expression and did not produce IFN-g ex vivo. Additionally, CD335 expression was lacking and no spontaneous target cell lysis could be detected in vitro, although perforin was detectable at a very low level. MHC class II and CD13 expression were also lacking. Following infection with foot-and-mouth disease virus, expression of CD62L and CD45RO was greatly reduced on WC1 gd T cells, and unexpectedly, CD45RO expression did not recover. A transient increase in expression of CD25 correlated with production of IFN-g. Expression of CD335 and production of perforin were detected on a subset of gd T cells, and this correlated with an increased spontaneous killing of xenogeneic target cells. Furthermore, increased MHC class II expression was detected on WC1 gd T cells, and these cells processed protein Ags. These activities are rapidly induced, within 3 d, and wane by 5 d following infection. All of these functions, NK-like killing, Ag processing, and IFN-g production, have been demonstrated for these cells in various species. However, these results are unique in that all these functions are detected in the same samples of WC1 gd T cells, suggesting a pivotal role of these cells in controlling virus infection. The Journal of Immunology, 2011, 186: 4853–4861.