CD39⁺ is expressed by a subset of CD45RO⁺CCR6⁺ T_REM cells. Cell-surface expression is shown for PBMCs gated for CD4⁺CD25^high, CD4⁺CD25^low and CD4⁺CD25^neg cells. Cells were stained with α-CD39 and counterstained with α-CD45RO, α-CCR6, α-CD49d, and with antibodies directed against the class II MHC molecules HLA-DR, HLA-DQ, and HLA-DP. Numbers in each quadrant indicate percentage of total cells.