Phosphate is essential for stimulation of Vγ9Vδ2 T lymphocytes by mycobacterial low molecular weight ligand

Abstract

T lymphocytes are divided into two subsets which express different T cell receptor heterodimers. In the peripheral blood of healthy individuals, the majority of T cells express the α/β T cell receptor (> 90%) while a minority have the γ/δ T cell receptor (< 10%). The γ/δ T cells of adults use preferentially the Vγ9Vδ2 chain combination. Although the stimulation requirements for γ/δ T lymphocytes are still undetermined, it has been reported that γ/δ T cells are not only stimulated, like α/β T cells, by conventional protein antigens and superantigens, but also by unusual ligands. Mycobacteria selectively stimulate Vγ9Vδ2 T cells, and a nonproteinacious low molecular weight fraction of 1–3 kDa has been identified as the tentative active component. Here, we confirm the nonproteinacious nature of this ligand, and show that it is comprised of unusual carbohydrate and phosphate. Importantly, cleavage of the terminal phosphate by alkaline phosphatase completely abrogates the stimulatory activity of the low molecular weight ligand for Vγ9Vδ2 T cells. Even mycobacterial whole lysate loses its stimulatory activity, for this T cell subset, after dephosphorylation with alkaline phosphatase. These findings identify phosphocarbohydrates as a novel molecular entity with selective stimlatory activity for a defined T cell subset.