Differential mRNA expression in circulating γδ T lymphocyte subsets defines unique tissue‐specific functions

To elucidate the functions of circulating γδ T cells, in the absence of antigen stimulation, the differential gene expression of two circulating γδ T cell subsets was analyzed. The two subsets, with distinct trafficking phenotypes in young calves, were GD3.5 + , CD8 − , WC1 + or GD3.5 − , CD2 + , WC1 − , and 90–100% CD8 + and were sorted based on GD3.5 and γδ T cell receptor expression. Results from two different human arrays probed with cDNA from these γδ T cell subsets indicated that they have markedly different tissue‐specific functions. The genes preferentially expressed by GD3.5 + (CD8 − ) γδ T cells demonstrated that they were highly activated, proliferative, and inflammatory, whereas those expressed by GD3.5 − (primarily CD8 + ) γδ cells were involved in promoting quiescence, consistent with a role for γδ T cells as sentinel mucosal cells, and several were interferon‐regulated genes. Gene expression and phenotypic assays indicated that CD8 + γδ T cells were apoptotic, whereas CD8 − γδ T cells were apoptosis‐resistant. Differential expression of multiple genes was confirmed in both arrays: That of 14 genes was confirmed by quantitative reverse transcriptase‐polymerase chain reaction and that of seven proteins was confirmed by flow cytometry. This novel, genomic analysis of circulating γδ T cell subsets, without confounding effects of the tissue microenvironment, offers new insight into the biology and development of neonatal γδ T cells.