IgE Production Beyond Classical T-Cell Help

IgE plays a central role in allergic diseases by binding to specific allergens and triggering the release of inflammatory mediators from mast cells and basophils. Conventionally, allergen-specific IgE is generated by T-cell-dependent mechanisms in which IL-4-producing CD4⁺ T helper cells, including Th2 cells and T follicular helper cells, orchestrate B cell class switch recombination to IgE. However, elevated IgE levels are also observed in diverse contexts, including primary immunodeficiencies and inflammatory conditions, where allergen involvement is less clear, suggesting the existence of additional pathways for IgE biogenesis. Supporting this notion, recent studies have identified alternative routes in which innate immune cells such as basophils or group 2 innate lymphoid cells provide bystander IL-4 to drive the production of IgE. In this review, we provide a comprehensive overview of IgE production pathways and examine how they operate across physiological and pathological conditions. Recognizing this mechanistic diversity will deepen our understanding of IgE biology beyond its role in allergy, highlighting its multifaceted contributions to barrier defense, protective immunity, and the pathogenesis of various inflammatory disorders.