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

Abstract

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.