Natural IgE promotes epithelial hyperplasia and inflammation-driven tumour growth

IgE is the least abundant circulating antibody class but is constitutively present in healthy tissues bound to resident cells via its high-affinity receptor, Fc{varepsilon}RI. The physiological role of endogenous IgE is unclear but it is suggested to provide host protection against a variety of noxious environmental substances and parasitic infections at epithelial barrier surfaces. Here we show that skin inflammation enhances levels of IgE with natural specificities and with a similar repertoire, VDJ rearrangements and CDRH3 characteristics as in healthy tissue. IgE-bearing basophils are recruited to inflamed skin via CXCL12 and TSLP/IL-3-dependent upregulation of CXCR4. In the inflamed skin, IgE/Fc{varepsilon}RI-signalling in basophils promotes epithelial cell growth and differentiation, partly through histamine engagement of H1R and H4R. Furthermore, this natural IgE response strongly drives tumour outgrowth of epithelial cells harbouring oncogenic mutation. These findings indicate that natural IgE support skin barrier defences however during chronic tissue inflammation this may be subverted to promote tumour growth.