Monitoring C5aR2 Expression Using a Floxed tdTomato-C5aR2 Knock-In Mouse.

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J Immunol. 2017 Nov 1;199(9):3234-3248. doi: 10.4049/jimmunol.1700710. Epub 2017 Sep 1.

Monitoring C5aR2 Expression Using a Floxed tdTomato-C5aR2 Knock-In Mouse.

CM Karsten;AV Wiese;F Mey;J Figge;TM Woodruff;T Reuter;O Scurtu;A Kordowski;LN Almeida;D Briukhovetska;KM Quell;J Sun;F Ender;I Schmudde;T Vollbrandt;Y Laumonnier;J Köhl

University of Lübeck, 23562, Germany. The University of Queensland, Brisbane, 4072, Australia. Cincinnati Children's Hospital and College of Medicine, University of Cincinnati, Cincinnati, OH 45229.

Service type: Knock-in mice


The biological significance of C5a receptor [(C5aR)2/C5L2], a seven-transmembrane receptor binding C5a and C5adesArg, remains ill-defined. Specific ligation of C5aR2 inhibits C5a-induced ERK1/2 activation, strengthening the view that C5aR2 regulates C5aR1-mediated effector functions. Although C5aR2 and C5aR1 are often coexpressed, a detailed picture of C5aR2 expression in murine cells and tissues is still lacking. To close this gap, we generated a floxed tandem dye (td)Tomato-C5aR2 knock-in mouse that we used to track C5aR2 expression in tissue-residing and circulating immune cells. We found the strongest C5aR2 expression in the brain, bone marrow, and airways. All myeloid-derived cells expressed C5aR2, although with different intensities. C5aR2 expression in blood and tissue neutrophils was strong and homogeneous. Specific ligation of C5aR2 in neutrophils from tdTomato-C5aR2 mice blocked C5a-driven ERK1/2 phosphorylation, demonstrating functionality of C5aR2 in the reporter mice. In contrast to neutrophils, we found tissue-specific differences in C5aR2 expression in eosinophils, macrophages, and dendritic cell subsets. Naive and activated T cells stained negative for C5aR2, whereas B cells from different tissues homogeneously expressed C5aR2. Also, NK cell subsets in blood and spleen strongly expressed C5aR2. Activation of C5aR2 in NK cells suppressed IL-12/IL-18-induced IFN-γ production. Intratracheal IL-33 challenge resulted in decreased C5aR2 expression in pulmonary eosinophils and monocyte-derived dendritic cells. In summary, we provide a detailed map of murine C5aR2 immune cell expression in different tissues under steady-state conditions and upon pulmonary inflammation. The C5aR2 knock-in mouse will help to reliably track and conditionally delete C5aR2 expression in experimental models of inflammation.

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