Patterns of A(2A) extracellular adenosine receptor expression in differentfunctional subsets of human peripheral T cells. Flow cytometry studies with anti-A(2A) receptor monoclonal antibodies

Signaling through A(2A) adenosine receptors (A(2A)R) regulates T lymphocyte expansion and modulates T cell receptor (TCR)mediated effector functions i n vitro. To understand the role of A(2A)Rs in the regulation of immune resp onse, we investigated the expression levels of this receptor in different f unctional lymphocyte subsets. Monoclonal anti-A(2A)R antibody was used to d evelop a flow cytometric assay to quantify the expression A(2A)Rs on lympho cytes. We report that detectable levels of expression of A(2A)Rs are much h igher among T cells than B cells. More CD4(+) than CD8(+) T cells express A (2A)Rs, but activation of T cells increases A(2A)R expression, predominantl y in CD8(+) T cells. No significant differences were found in the proportio n of A(2A)R(+) cells between CD8(low) and CD8(high) T cells or between TCR/ CD3(low) and TCR/CD3(high) T cells. Studies of T helper cell subsets (T(H)1 and T(H)2) reveal that lymphokine-producing cells are much more likely to express A(2A)Rs than are cells that do not produce lymphokines. These resul ts suggest that A(2A)Rs are variably expressed on T cell subsets and may re gulate cytokine production in activated T lymphocytes.