Expression of T-Bet, Eomesodermin, and GATA-3 Correlates With Distinct Phenotypes and Functional Properties in Porcine γδ T Cells.

Unlike mice and humans, porcine gamma delta T cells represent a prominent subset of T cells in blood and secondary lymphatic organs. GATA-3, T-bet and Eomesodermin (Eomes) are transcription factors with crucial functions in T-cell development and functional differentiation, but their expression has not been investigated in porcine gamma delta T cells so far. We analyzed the expression of these transcription factors in gamma delta thymocytes, mature gamma delta T cells from blood, spleen, lymph nodes, and lung tissue as well as in vitro stimulated gamma delta T cells on the protein level by flow cytometry. GATA-3 was present in more than 80% of all gamma delta-thymocytes. Extra-thymic CD2(-) gamma delta T cells expressed high levels of GATA-3 in all investigated organs and had a CD8 alpha(-/dim)CD27(+)perforin(-) phenotype. T-bet expression was mainly found in a subset of CD2(+) gamma delta T cells with an opposing CD8 alpha(high)CD27(dim/-)perforin(+) phenotype. Eomes(+) gamma delta T cells were also found within CD2(+) gamma delta T cells but were heterogeneous in regard to expression of CD8 alpha, CD27, and perforin. Eomes(+) gamma delta T cells frequently co-expressed T-bet and dominated in the spleen. During aging, CD2-GATA-3(+) gamma delta T cells strongly prevailed in young pigs up to an age of about 2 years but declined in older animals where CD2(+) T-bet(+) gamma delta T cells became more prominent. Despite high GATA-3 expression levels, IL-4 production could not be found in gamma delta T cells by intracellular cytokine staining. Experiments with sorted and ConA + IL-2 + IL-12 + IL-18-stimulated CD2(-) gamma delta T cells showed that proliferating cells start expressing CD2 and T-bet, produce IFN-gamma, but retain GATA-3 expression. In summary, our data suggest a role for GATA-3 in the development of gamma delta-thymocytes and in the function of peripheral CD2(-)CD8 alpha(-/dim)CD27(+)perforin(-) gamma delta T cells. In contrast, T-bet expression appears to be restricted to terminal differentiation stages of CD2(+) gamma delta T cells, frequently coinciding with perforin expression. The functional relevance of high GATA-3 expression levels in extra-thymic CD2(-) gamma delta T cells awaits further clarification. However, their unique phenotype suggests that they represent a thymus-derived separate lineage of gamma delta T cells in the pig for which currently no direct counterpart in rodents or humans has been described.