The role of the anaphylatoxin C5a in intestinal immune responses
Zusammenfassung der Projektergebnisse
The anaphylatoxins C3a and C5a and their cognate anaphylatoxin receptors play important roles in the activation and regulation of innate immune cells. While a body of data has accumulated showing critical roles of C5a-mediated activation of C5aR and C5aR2 on macrophages and dendritic cells (DC) in the airway and the lung for the development of pulmonary allergy, less is known about anaphylatoxin receptor expression in intestinal phagocytes and DCs and the functional impact of their activation. We generated floxed anaphylatoxin receptor reporter mice that we used to monitor C3aR, C5aR1 and C5aR2 expression in phagocytes and conventional DCs (cDC) from the lamina propria (LP) of the small intestine. We found that CD11b+F4/80+MHCII+ phagocytes strongly expressed all three anaphylatoxin receptors. In contrast, C5aR1 was absent in CD103+ or CD11bhi cDCs from LP and C5aR2 was only marginally expressed in such cDC subsets. About 10% of CD103+ and 20% of CD11bhi cDCs expressed C3aR. Given that several subsets of antigen-presenting cells in the LP express anaphylatoxin receptors, we determined the potential impact of the C5a/C5aR1 axis on the composition and diversity of the gut microbiota. Our results demonstrate a significant influence of the C5ar1 genotype on numerous aspects of microbial community composition and structure at several different anatomical locations, in addition to influences of sex at some locations. This includes differences in the abundance of Firmicutes and Proteobacteria in the cecum and colon and Actinobacteria in the jejunum. Alpha diversity analyses revealed corresponding differences in evenness (Shannon index) with respect to the C5ar1 genotype in the jejunum. Further, beta diversity analyses also showed significant differences between genotypes in the cecum. Taken together, we uncovered a novel role for the C5a/C5aR1 axis on microbiota composition and diversity of the intestine. Food allergy is associated with changes in the intestinal microbiota or dysbiosis early in life. Further, decreased bacterial diversity is one important factor that predisposes to food allergy. Our findings regarding the impact of the C5a/C5aR1 axis on microbiota composition and diversity of the intestine suggest that the C5a/C5aR1 axis may have an impact on the development of food allergy. So far, the involvement of the C5a/C5aR1 axis in the development of food allergy has not been assessed. Thus, we determined the role of C5a for the development of food allergy in vivo and in vitro. We subjected C5ar1-/- and wild-type (wt) BALB/c mice to oral ovalbumin (OVA)- induced anaphylaxis. We observed that 78% of wt but only 9% of C5ar1-/- mice suffered from diarrhea and hypothermia after the 7th oral OVA challenge. Importantly, peritoneal MCs strongly expressed C5aR1 after the 7th oral OVA treatment. OVA-specific serum IgE and MCPT-1 levels were significantly decreased in C5aR1-deficient as compared with wt mice. To directly examine the impact of the C5a/C5aR1 axis on MC function, we generated bone marrow-derived MCs (BMMCs) and tested their activation and degranulation potency in response to FcεR1 cross-linking. Degranulation of C5ar1-/- BMMCs was reduced by 50% and IL-6 production was decreased by 35% as compared with wt cells. Also, FcεR1 cross-linking markedly upregulated C5aR1 MC expression. Further, in contrast to wt mice, C5ar1-/- mice were largely protected from histamine-induced temperature drop in vivo. In line with this finding, C5aR-targeting protected human endothelial cells from histamine-induced barrier dysfunction and disruption of tight junction proteins in vitro. Our findings identify a critical role of the C5a/C5aR1 axis in IgE-mediated oral antigen-induced anaphylaxis. C5aR1 may serve as a novel therapeutic target to suppress the inflammatory response in food-induced anaphylaxis.
Projektbezogene Publikationen (Auswahl)
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C5aR-dependent cell activation by physiological concentrations of C5adesArg: insights from a novel label-free cellular assay. 2012 J. Immunol. 189:4797-4805
Reis S.E., Chen H., Sfyroera G., Monk P.N., Köhl J., Ricklin D., Lambris J.D.
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C3a modulates IL-1ß secretion in human monocytes by regulating ATP efflux and subsequent NLRP3 inflammasome activation. 2013 Blood 122:3473-3481
Asgari E., Le Friec G., Yamamoto, H., Perucha E., Sacks S.S., Köhl J., Cook H.T., Kemper C.
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Functional analysis of C5a effector responses in vitro and in vivo. Methods Mol. Biol. 2014 1100:291-304
Karsten C.M., Laumonnier Y., Köhl J.
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Monitoring and cell-specific deletion of C5aR1 using a novel floxed GFP-C5aR1 reporter knockin mouse. 2015 J. Immunol. 194:1841-1855
Karsten C.M., Laumonnier Y., Eurich B., Ender F., Bröker K., Roy S., Czabanska A., Vollbrandt T., Figge J., Köhl J.
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(2016): Autocrine NLPR3 inflammasome activity is critical to normal adaptive immunity via regulation of IFN-γ in CD4+ T cells. In: The Journal of Immunology 196 (1 Supplement), 58.6-58.6
Arbore G, West EE, Robertson AAB, Klos A, Rheinheimer C, Dutow P, Woodruff TM, O’Neill LA, Coll RC
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Monitoring C3aR expression using a novel floxed tdTomato-C3aR knock-in mouse. 2017 J. Immunol.
Quell KM, Karsten CM, Kordowski A, Almeida L, Briukhovetska D, Wiese AV, Sun J, Ender F, Antoniou K, Schröder T, Schmudde I, Berger JL, König P, Vollbrandt T, Laumonnier Y, Köhl J
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Novel insights into the expression pattern of anaphylatoxin receptors in mice and men. Mol. Immunol. 2017
Laumonnier Y, Karsten CMK, Köhl J
