IGHE and Allergy: Mouse models of allergen immunotherapy are challenging for the following reasons: allergy mouse models rely on allergen application in context with Th2 adjuvants (often by nonphysiological routes) and thereby induce robust disease that is difficult to modulate; symptomatic allergy in mice is, unlike in humans, associated with IgE and IgG1; mice express Tregs, but do not harbor IgG4 antibodies which is an important biomarker in human allergen immunotherapy [1].