Chemotactic activity of extracellular nucleotideson human immune cells.

Purinergic P2 receptors are a class of plasma membrane receptors that are express in many tissues and are ligated by extracellular nucleotides [such as adenosine triphosphate (ATP), adenosine diphosphate (ADP), uridine 5–triphosphate (UTP) and uridine 5–diphosphate (UDP)], which are released as a consequence of cell damage, cell stress, bacterial infection or other noxious stimuli. According to the molecular structure, P2 receptors are divided into two subfamilies: P2X and P2Y receptors. The P2X receptors are ligand-gated channels, whereas P2Y receptors are G-protein-coupled seven-membrane-spanning receptors. Several studies indicate that nucleotides play an important role in immune response modulation through their action on multiple cell types, including monocytes, mast cells, dendritic cells, neutrophils, and eosinophils. Recent work by our group and others identified extracellular nucleotides as chemotaxins for various human immune cells, including eosinophils, neutrophils and dendritic cells. In this review, we summarise recent findings in this field and put forward a hypothesis on the role of P2 receptors in the early recruitment of human immune cells to the site of inflammation

The P2Y14 receptor of airway epithelial cells coupling to intracellular Ca2+and IL-8 secretion

Uridine nucleotides and UDP-glucose are endogenous molecules, which are released into the extracellular environment in a lytic manner after cell damage, as well as by regulated nonlytic mechanisms. Recently, a UDP-glucose-specific d protein-coupled P2Y receptor, namely P2Y14, has been cloned. In this study, we demonstrated expression of the P2Y14mRNA in human lung epithelial cells and in the epithelial cell lines A549 and BEAS-2B. Evidence of functional expression of the P2Y14receptor in these cell lines was provided by calcium measurements after stimulation with uridine 5â\u80²-diphosphoglucose (UDP-glc). Experiments with pertussis toxin and the Ca2+-chelator ECTA revealed participation of pertussis toxin-sensitive Gi/o-proteins in the mobilization of Ca2+-ions from intracellular stores by UDP-glc. Moreover, UDP-glc increased secretion of the potent neutrophil chemoattractant CXCL8/IL-8 in A549 and BEAS-2B cells in a pertussis toxin-sensitive manner. Moreover, reverse transcription and quantitative polymerase chain reaction revealed that UDP-glc modulated mRNA levels of IL-8/CXCL8. However, stimulation of A549 and BEAS-2B cells with UDP-glc neither modified basal nor cytokine-induced secretion of the CXC-chemokines CXCL9/MIG, CXCL10/IP-10, and CXCL11/I-TAC. In addition, UDP-glc did not affect proliferation of the two cell lines. In summary, our data provide evidence for a distinct physiologic role of P2Y14in the selective release of specific chemokines from human airway epithelial cells

Expression of interleukin-13 receptor α 1-subunit on peripheral blood eosinophils is regulated by cytokines

Interleukin-13 (IL-13) is critical for the development of allergic asthma and is involved in the activation of eosinophils within the airways. IL-13 exerts its activity on target cells via the dimeric IL-13 receptor (IL-13R), which comprises the IL-13 receptor α1-chain (IL-13Rα1) as a specific component. The aim of this study was to investigate the expression of the IL-13Rα1-chain on primary human eosinophilic granulocytes. Furthermore, it addresses the regulatory influence of cytokines on the level of surface abundance of this receptor subunit. Expression of IL-13- and IL-4-receptor subunits in purified primary human eosinophils was monitored at the messenger RNA level by reverse transcription polymerase chain reaction and at the protein level by flow cytometry. For the analysis of IL-13Rα1 surface expression, a new monoclonal antibody, which was generated using genetic immunization, was employed. Different cytokines with established activity on eosinophils were studied with regard to their influence on IL-13Rα1 in vitro by flow cytometry. Whereas IL-13 and IL-4 had inhibitory effects on IL-13Rα1 expression on eosinophils, interferon-γ, tumour necrosis factor-α, and, to the largest extent, transforming growth factor-β, enhanced the expression of this receptor subunit. A positive regulatory response evoked by transforming growth factor-β and interferon-γ does not prevent inhibitory effects caused by IL-13. These findings suggest a regulatory cytokine network influencing the reactivity of eosinophils to IL-13