Purinergic P2X7 receptor function in lung alveolar macrophages: Pharmacologic characterization and bidirectional regulation by Th1 and Th2 cytokines

Abstract

AbstractPurinergic P2X7 receptors have been shown in the lung, but little is known concerning P2X7 function in pulmonary macrophages. In this study we characterized P2X7‐dependent responses to extracellular ATP in resident and activated alveolar macrophages (AM) obtained by bronchoalveolar lavage of rats. Incubation of AM with high concentrations of ATP (5mM) or 3′‐O‐(4‐benzoyl)benzoyl‐ATP (BzATP) (0.5mM), a P2X7 agonist, induced: 1) rapid pore formation, 2) apoptosis, and 3) enhanced release of IL‐1α, IL‐1β, and IL‐6, but not TNF‐α following priming with lipopolysaccharide (LPS). Furthermore, higher expression of P2X7 receptor in AM was associated with increased formation of Type 2 multinucleated giant cells (Type 2 MGC) in response to GMCSF. Immunopharmacological analysis also showed that P2X7‐dependent pore formation in AM was significantly increased by LPS (1 µg/ml) and the T helper 1 (Th1) cytokines, interferon‐γ (100U/ml), and, to a lesser extent, TNF‐α (>20 ng/ml). In contrast, the T helper 2 (Th2) cytokines IL‐4 (1pg/ml) as well as IL‐10 (1ng/ml) significantly inhibited these P2X7 receptor functions. Transforming growth factor‐β (TGF‐β), a known deactivator of macrophages, had no significant effect. Our results demonstrate that AM exhibit all the characteristics of a functional P2X7 receptor which upon appropriate stimulation activates the proinflammatory IL‐1→IL‐6 cytokine cascade and the formation of MGC, a hallmark of granulomatous reactions. Moreover, Th1 and Th2 cytokines reciprocally regulate P2X7 function, suggesting a role for P2X7 in pulmonary diseases associated with chronic inflammatory responses. Drug Dev. Res. 59:118–127, 2003. © 2003 Wiley‐Liss, Inc.