A novel role for the C5a/C5aR1 axis in food allergy.

In a joint effort, the Köhl lab at the University of Lübeck and the Hogan lab at Cincinnati Children's Hospital uncovered a novel role for the C5a/C5aR1 axis in food allergy.

Food-induced anaphylaxis is a serious allergic reaction caused by Fce-receptor activation on mast cells (MCs).The exact mechanisms breaking oral tolerance and the effector pathways driving food allergy remain elusive. As complement is activated in food-induced anaphylaxis, the researchers aimed to assess the role of C5a in disease pathogenesis. Oral antigen-induced food-induced anaphylaxis was induced in BALB/c wildtype (wt) and C5ar1^-/- mice. Readouts included diarrhea development, changes in rectal temperature, hematocrit, antigen-specific serum IgE, MCPT-1 and intestinal MC numbers as well as FcεR1-mediated MC functions including C5a receptor 1 (C5aR1) regulation. Further, histamine-mediated hypothermia and regulation of endothelial tight junctions were determined. 

Repeated oral OVA challenge resulted in diarrhea, hypothermia, increased hematocrit, high OVA-specific serum IgE and MCPT-1 levelsin wt mice. Male C5ar1-/-mice were completely whereas female C5ar1^-/- were partially protected from anaphylaxis development. Serum MCPT-1 levels were reduced gender-independent, whereas IgE levels were reduced in male but not in female C5ar1^-/- mice. Mechanistically, IgE-mediated degranulation and IL-6 production from C5ar1^-/- BMMCs of both sexes were significantly reduced. Importantly, FcεR1 cross-linking strongly upregulated C5aR1 MC expression in vitroand in vivo. Finally, C5ar1^-/- male mice were largely protected from histamine-induced hypovolemic shock, which was associated with protection from histamine-induced barrier dysfunction in vitrofollowing C5aR targeting. Thesefindings identify C5aR1 activation as an important driver of IgE-mediated food allergy through regulation of allergen specific IgE production, FcεR1-mediated MC degranulation and histamine-driven effector functions preferentially in male mice. They suggest that C5aR1 may serve as potential new therapeutic target in this emerging disease.