gamma delta T cells in artiodactyls: Focus on swine

Vaccination is the most effective medical strategy for disease prevention but there is a need to improve livestock vaccine efficacy. Understanding the structure of the immune system of swine, which are considered a gamma delta T cell "high" species, and thus, particularly how to engage their gamma delta T cells for immune responses, may allow for development of vaccine optimization strategies. The propensity of gamma delta T cells to home to specific tissues, secrete pro-inflammatory and regulatory cytokines, exhibit memory or recall responses and even function as antigen presenting cells for alpha beta T cells supports the concept that they have enormous potential for priming by next generation vaccine constructs to contribute to protective immunity. gamma delta T cells exhibit several innate-like antigen recognition properties including the ability to recognize antigen in the absence of presentation via major histocompatibility complex (MHC) molecules enabling gamma delta T cells to recognize an array of peptides but also non peptide antigens in a T cell receptor-dependent manner. gamma delta T cell subpopulations in ruminants and swine can be distinguished based on differential expression of the hybrid co-receptor and pattern recognition receptors (PRR) known as workshop cluster 1 (WC1). Expression of various PRR and other innate-like immune receptors diversifies the antigen recognition potential of gamma delta T cells. Finally, gamma delta T cells in livestock are potent producers of critical master regulator cytokines such as interferon (IFN)-gamma and interleukin (IL)-17, whose production orchestrates downstream cytokine and chemokine production by other cells, thereby shaping the immune response as a whole. Our knowledge of the biology, receptor expression and response to infectious diseases by swine gamma delta T cells is reviewed here.