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Chuan-Hui Kuo, Andrea Collins, Masaharu Ohbayashi, Santa Ono; Chemokine C-C motif ligand 7 as a Costimulatory Signal on Mast Cell Activation and Motility. Invest. Ophthalmol. Vis. Sci. 2013;54(15):2046.
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Molecules that are necessary for ocular hypersensitivity reactions include the chemokine receptors CCR1 and CCR3; CC chemokine ligand (CCL) 7 is a genetic target and ligand for these receptors. The goal of this study is to explore the role of CCL7 in mast cell activity and motility response to costimulation via FcεRI and CCR1 engagements.
BALB/c mice were sensitized with OVA/alum intraperitoneally and subjected to OVA-induced ocular anaphylaxis via eye drops. Gene expressions in the conjunctival tissue were examined using RT-qPCR. Rat basophilic leukemia-2H3 cells expressing human CCR1 (RBL-CCR1) and bone marrow derived mast cell (BMMC) were sensitized and activated with antigen and/or recombinant human CCL7. β-hexosaminidase activity was measured by incubating the supernatants with p-nitrophenyl N-acetyl-β-D-glucosamide. The chemotaxis assay was performed using TranswellTM chambers with 8µm diameter membrane pores. Morphological changes were observed through immunostaining; cells were fixed and processed for polymerized actin staining with TRITC-conjugated phalloidin.
CCL7 was upregulated in coujunctiva tissue in OVA-induced anaphylaxis compared to controls. The presence of recombinant human CCL7, combined with IgE and antigen treatment, synergistically enhanced degranulation when compared to cells treated with only IgE and its respective antigen in RBL-CCR1 and BMMC. RBL-CCR1 cells stimulated with CCL7 showed chemotactic increase in a dose dependent manner and dramatic membrane ruffling. In contrast, RBL-CCR1 cells costimulated with antigen and CCL7 exhibited less membrane ruffling and inhibited chemotaxis when compared with CCL7-stimulated cells.
Our results demonstrate that the chemokine CCL7 is upregulated in OVA-induced ocular anaphylaxis in vivo and can enhance mast cell chemotaxis in vitro. The cross-talk between FcεRI- mediated and CCR-mediated signaling pathway induces activation and arrested chemotaxis of mast cells, thus contributing to allergic inflammation. Combined treatment with antigen and CCL7 decreases membrane ruffle formation in RBL-CCR1 cells, suggesting that the decreased ruffling response involves the inhibition of chemotaxis due to the costimulation. A better understanding of the roles played by CCL7 will provide insights into mast cell function and ideas for novel treatments for allergic ocular diseases.
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