Cutting edge: Purinergic signaling regulates radical-mediated bacterial killing mechanisms in macrophages through a P2X₇-independent mechanism

Signaling by extracellular nucleotides through P2 purinergic receptors affects diverse macrophage functions; however, its role in regulating antimicrobial radicals during bacterial infection has not been investigated. Mycobacterium tuberculosis-infected macrophages released ATP in a dose- dependent manner, which correlated with nitrite accumulation. P2 receptor inhibitors, including oxidized ATP, blocked NO synthase (NOSII) up-regulation and NO production induced by infection with M. tuberculosis or bacille Calmette-Guerin, or treatment with LPS or TNF-α. Oxidized ATP also inhibited oxygen radical production and activation of NF-κB and AP-1 in response to infection and inhibited NO-dependent killing of bacille Calmette-Guerin by macrophages. Experiments using macrophages derived from P2X₇ gene-disrupted mice ruled out an essential role for P2X₇ in NOSII regulation. These data demonstrate that P2 receptors regulate macrophage activation in response to bacteria and proinflammatory stimuli, and suggest that extracellular nucleotides released from infected macrophages may enhance production of oxygen radicals and NO at sites of infection.