CD27 expression discriminates porcine T helper cells with functionally distinct properties

Differentiation of porcine T helper cells is still poorly investigated, partly due to a lack of monoclonal antibodies (mAbs) specific for molecules involved in this process. Recently, we identified a mAb specific for porcine CD27 and showed that CD27 is expressed by all naïve CD8α(-) T helper cells but divides CD8α(+) T helper cells into a CD27(+) and a CD27(-) subset. In the present study, detailed phenotypical and functional analyses of these T-helper cell subpopulations were performed. Naïve CD8α(-)CD27(+) T helper cells predominantly resided in various lymph nodes, whereas higher proportions of CD8α(+)CD27(+) and CD8α(+)CD27(-) T helper cells were found in blood, spleen and liver. Both CD8α(+)CD27(+) and CD8α(+)CD27(-) T helper cells were capable of producing IFN-γ upon in vitro polyclonal stimulation and antigen-specific restimulation. Experiments with sorted CD8α(-)CD27(+), CD8α(+)CD27(+) and CD8α(+)CD27(-) T-helper cell subsets following polyclonal stimulation revealed the lowest proliferative response but the highest ability for IFN-γ and TNF-α production in the CD8α(+)CD27(-) subset. Therefore, these cells resembled terminally differentiated effector memory cells as described in human. This was supported by analyses of CCR7 and CD62L expression. CD8α(+)CD27(-) T helper cells were mostly CCR7(-) and had considerably reduced CD62L mRNA levels. In contrast, expression of both homing-receptors was increased on CD8α(+)CD27(+) T helper cells, which also had a proliferation rate similar to naïve CD8α(-)CD27(+) T helper cells and showed intermediate levels of cytokine production. Therefore, similar to human, CD8α(+)CD27(+) T helper cells displayed a phenotype and functional properties of central memory cells.