Divergent IgE to IgG hypermutation is associated with allergic hypothermia in mice

Methods

A murine model of hen's egg allergy with the major allergens ovalbumin (OVA) and ovomucoid (OVO) was employed to investigate allergen-induced induced anaphylaxis (detected as hypothermia). Deep sequencing of IgE and IgG1 was used to identify IgE clones with divergent hypermutation profiles compared to their clonally related IgG progenitors. Binding to OVA and OVO was predicted by in silico analysis.

IgG-mediated blockade of IgE binding to OVA and OVO was tested by ELISA. Results: A small subset of IgE clones acquired somatic CDR3 hypermutations that were absent in their clonally related IgG1 progenitors, these clones were called "divergent" IgE. The presence and clonal expansion of highly mutated divergent IgE clonotypes correlated with the development of allergen-induced severe hypothermia.

In contrast and independent of their hypermutation rate, the presence of other IgE clones did not correlate with allergic hypothermia. Predictive analysis suggests that the relevant divergent IgE clonotypes predominantly reacted to OVO rather than OVA. Serum IgG from allergic mice could block binding of OVA-specific but not OVO-specific IgE.

Divergent IgE was also observed in the bone marrow (BM) of allergic patients. Conclusion: This study identifies a small subset of highly hypermutated “divergent IgE clonotypes” associated with severe anaphylaxis and provides a possible mechanism by which allergy-promoting IgE escape from competition by IgG progenitor clones.