Phenotypic and functional differentiation of porcine αß T cells: current knowledge and available tools.

Domestic pigs are considered as a valuable large animal model because of their close relation to humans in regard to anatomy, genetics and physiology. This includes their potential use as organ donors in xenotransplantation but also studies on various zoonotic infections affecting pigs and humans. Such work also requires a thorough understanding of the porcine immune system which was partially hampered in the past by restrictions on available immunological tools compared to rodent models. However, progress has been made during recent years in the study of both, the innate and the adaptive immune system of pigs. In this review we will summarize the current knowledge on porcine αß T cells, which comprise two major lymphocyte subsets of the adaptive immune system: CD4(+) T cells with important immunoregulatory functions and CD8(+) T cells, also designated as cytolytic T cells. Aspects on their functional and phenotypic differentiation are presented. In addition, we summarize currently available tools to study these subsets which may support a more widespread use of swine as a large animal model.

IL-12 and IL-18 induce interferon-γ production and de novo CD2 expression in porcine γδ T cells.

γδ T cells are highly abundant in the blood and spleen of pigs but little is known about their functional differentiation. In this study the potential of the type-1 polarizing cytokines IL-12 and IL-18 in combination with IL-2 and Concanavalin A (ConA) to stimulate porcine γδ T cells was investigated. Stimulation of purified γδ T cells with ConA and IL-2 induced a strong proliferation of CD2(-) γδ T cells, whereas additional stimulation with IL-12 and IL-18 caused a stronger proliferation of CD2(+) γδ T cells. IFN-γ could only be detected in supernatants of γδ T-cell cultures supplemented with IL-12 and IL-18. Experiments with sorted CD2/SWC5-defined γδ T-cell subsets revealed that CD2(+)SWC5(-) γδ T cells are the main producers of IFN-γ following stimulation with IL-2/IL-12/IL-18. Additional stimulation with ConA led to an upregulation of CD2 within the CD2(-) γδ T cell subsets, indicating a previously unnoticed plasticity of CD2-defined γδ T cell subsets.

CD2 and CD8α define porcine γδ T cells with distinct cytokine production profiles.

γδ T cells are a remarkably prominent T-cell subset in swine with a high prevalence in blood. Phenotypic analyses in this study showed that CD2(-) γδ T cells in their vast majority had a CD8α(-)SLA-DR(-)CD27(+) phenotype. CD2(+) γδ T cells dominated in spleen and lymph nodes and had a more heterogeneous phenotype. CD8α(+)SLA-DR(-)CD27(+) γδ T cells prevailed in blood, spleen and lymph nodes whereas in liver a CD8α(+)SLA-DR(+)CD27(-) phenotype dominated, indicating an enrichment of terminally differentiated γδ T cells. γδ T cells were also investigated for their potential to produce IFN-γ, TNF-α and IL-17A. Within CD2(+) γδ T cells, IFN-γ and TNF-α single-producers as well as IFN-γ/TNF-α double-producers dominated, which had a CD8α(+)CD27(+/-) phenotype. IL-17A-producing γδ T cells were only found within CD2(-) γδ T cells, mostly co-produced TNF-α and had a rare CD8α(+)CD27(-) phenotype. However, quantitatively TNF-α single-producers strongly dominated within CD2(-) γδ T cells. In summary, our data identify CD2 and CD8α as important molecules correlating with functional differentiation.

Phenotypic maturation of porcine NK- and T-cell subsets.

Detailed information concerning the development of the immune system in young pigs is still rudimental. In the present study, we analyzed changes in phenotype and absolute numbers of natural killer cells, γδ T cells, T helper cells, regulatory T cells and cytolytic T cells in the blood of pigs from birth to six months of age. For each lymphocyte subpopulation, a combination of lineage and differentiation markers was investigated by six-color flow cytometry. Major findings were: (i) absolute numbers of γδ T cells strongly increased from birth until 19-25 weeks of age, indicating an important role for these cells during adolescence; (ii) phenotype of T helper cells changed over time from CD8α(-)SLA-DR(-)CD27(+) towards CD8α(+)SLA-DR(+)CD27(-) but CD45RC(-) T helper cells were found immediately after birth, therefore questioning the role of this marker for the identification of T-helper memory cells; (iii) for cytolytic T cells, putative phenotypes for early effector (CD3(+)CD8αß(+)perforin(+)CD27(dim)) and late effector or memory cells (CD3(+)CD8αß(+)perforin(+)CD27(-)) could be identified.