Porcine γδ T cells: Possible roles on the innate and adaptive immune responses following virus infection

γδ T cells recognise different types of antigen in alternative ways to αβ T cells, and thus appear to play a complementary role in the immune response. However, unlike αβ T cells, the role or function of γδ T cells is still unclear. As pigs possess a high proportion of circulating γδ T cells, they are suitable large animal model to study γδ T cell functions. This as yet has not been fully exploited, leaving porcine γδ T cell biology and its role in immunity in its infancy. Foot-and-mouth disease (FMD) high potency “emergency” vaccines are able to induce early protection from challenge and it has been suggested that, in part, there is some involvement of innate immune responses. The antigen component of the vaccine is able to stimulate purified naïve pig γδ T cells and induce the mRNA of various cytokines and chemokines. This observation suggests that γδ T cells probably contribute to the early phase of the immune responses to FMD vaccination, and perhaps infection. A subset of these circulating γδ T cells display a phenotype similar to professional antigen presenting cells and are able to take up and present soluble antigen to CD4+ T cells in a direct cell–cell interaction via MHC class II. This direct interaction between γδ T cells and CD4+ T cells is likely to have a significant influence on the out come of the adaptive immune response.