Adenosine production by human B cells and B cell-mediated suppression of activated T cells

Antibody-independent role of B cells in modulating T-cell responses is incompletely understood. Freshly isolated or cultured B cells isolated from the peripheral blood of 30 normal donors were evaluated for CD39 and CD73 coexpression, the ability to produce adenosine 5'-monophosphate (AMP) and adenosine (ADO) in the presence of exogenous adenosine triphosphate (ATP) as well as A(1), A(2A), A(2B), and A(3) adenosine receptor (ADOR) expression. Human circulating B cells coexpress ectonucleotidases CD39 and CD73, hydrolyze exogenous ATP to 5'-AMP and ADO, and express messenger RNA for A(1)R, A(2A)R, and A(3)R. 2-chloroadenosine inhibited B-cell proliferation and cytokine expression, and only A(3)R selective antagonist restored B-cell functions. This suggested that B cells use the A(3)R for autocrine signaling and self-regulation. Mediated effects on B-cell growth +/- ADOR antagonists or agonists were tested in carboxyfluorescein diacetate succinimidyl ester assays. In cocultures, resting B cells upregulated functions of CD4(+) and CD8(+) T cells. However, in vitro-activated B cells downregulated CD73 expression, mainly produced 5'-AMP, and inhibited T-cell proliferation and cytokine production. These B cells acquire the ability to restrict potentially harmful effects of activated T cells. Thus, B cells emerge as a key regulatory component of T cell-B cell interactions, and their dual regulatory activity is mediated by the products of ATP hydrolysis, 5'-AMP, and ADO.