described localization in SKI-II chemical information circulating immune cells. Immunoblotting of EGFP cell extracts with the P2Y14 antibody showed a predominant 50-KDa band and a weaker 40-kDa band. We then performed a radiolabeled UDP-glucose binding assay using total membranes separated from FACS isolated EGFP cells and EGFP cells. The UDP-glucose binding measured in EGFP cells was displaced PubMed ID:http://www.ncbi.nlm.nih.gov/pubmed/1975559 with a saturating concentration of cold UDP-glucose, but not with ATP, showing UDP-glucose-specific binding. In contrast, in EGFP cells no UDP- 10 / 24 Immune Role of P2Y14 in Intercalated Cells Fig 4. Expression 
of P2Y14 in EGFP cells. Representative immunoblot profile of P2Y14 in two EGFP cell samples isolated by FACS. Binding of UDP-glucose to total membranes prepared from FACS isolated EGFP and EGFP cells in the presence or absence of a saturating concentration of unlabeled UDP-glucose or ATP. Data are represented as fold changes compared to the binding measured in the presence of unlabeled UDP-glucose. Each bar represent the average of 3 independent experiments each performed in triplicate. Values are expressed as mean SEM, P<0.05. doi:10.1371/journal.pone.0121419.g004 glucose-specific binding was measured. Altogether, these data show that ICs are the only renal epithelial cells that express P2Y14. P2Y14 activation up-regulates pro-inflammatory chemokine mRNAs in intercalated cells To determine whether P2Y14 activation induces the upregulation of pro-inflammatory mRNAs in ICs in vivo, we injected B1-EGFP mice through the tail vein with either a saline solution or a solution containing 100 M UDP-glucose. Kidneys were harvested 4 h later and processed for FACS isolation of EGFP cells, mRNA extraction and real-time PCR to measure pro-inflammatory chemokine and cytokine expression. To avoid contamination of blood immune cells, which also express P2Y14, we flushed the blood out of the kidneys by perfusing mice with PBS through the cardiac left ventricle. In addition, maximum purity of EGFP cells was obtained by restricting the sorting parameters to isolate only the brightest EGFP cells. Cytospin smears of EGFP cells immunostained for CD45 did not show any contamination of the samples with leukocytes. We were thus confident that any changes in pro-inflammatory mediator expression following P2Y14 activation with UDP-glucose were attributed to the presence of the receptor in ICs uniquely. As shown in Fig. 5, the neutrophil chemo-attractants, CXCL1 and CXCL2 had significantly higher expression levels following UDP-glucose treatment in vivo for 4 hours. A significant increase was also observed for the monocyte chemo-attractant CCL2 and CCL3. No effect was observed after 2, 6, or 12 hours. In addition, no significant changes were observed for CCL4, CCL5, TNF, IL1, and IL6 expression at any time point. These results show that ICs produce pro-inflammatory mediators in vivo following activation by a pro-inflammatory agonist, and that this process can be efficiently promoted through UDP-glucose/P2Y14 signaling. 11 / 24 Immune Role of P2Y14 in Intercalated Cells Fig 5. Quantitative PCR detection of pro-inflammatory mediators in EGFP cells. EGFP cells were isolated by FACS from B1-EGFP mice 4h after an i.v. injection with saline or with saline containing 100 M UDP-glucose. All values are normalized to GAPDH. Data are represented as % changes relative to control. Values PubMed ID:http://www.ncbi.nlm.nih.gov/pubmed/19755711 are mean SEM, P<0.05, P<0.001. doi:10.1371/journal.pone.0121419.g005 Characterization of the P2Y14 signaling pathway i