Recent evidence has highlighted the critical role of memory cells in maintaining lifelong food allergies, thereby identifying these cells as therapeutic targets. IgG⁺ memory B cells replenish pools of IgE-secreting cells upon allergen exposure, which contract thereafter due to the short lifespan of tightly regulated IgE-expressing cells. Advances in the detection and highly dimensional analysis of allergen-specific B and T cells from allergic patients have provided insight on their phenotype and function. The newly identified Th2A and Tfh13 populations represent a leap in our understanding of allergen-specific T cell phenotypes, though how these populations contribute to IgE memory responses remains poorly understood. Within, we discuss the mechanisms by which memory B and T cells are activated, integrating knowledge from human systems and fundamental research. We then focus on memory reactivation; specifically, on the pathways of secondary IgE responses. Throughout, we identify areas of future research which will help identify immunotargets for a transformative therapy for food allergy.

In contrast to Th1 immune responses against pathogenic viruses and bacteria, the incipient events that generate Th2 responses remain less understood. Part of the difficulty in identifying universal operating principles stems from the diversity of entities against which cellular and molecular Th2 responses are produced. Indeed, such responses are launched towards harmful macroscopic parasites and noxious substances such as venoms but also against largely innocuous allergens. This suggests that the canonical understanding about sensing and recognition applied to Th1 responses may not be translatable to Th2 responses. This review will discuss processes and signals known to occur in Th2 responses, particularly in the context of food allergy. We propose that perturbations of homeostasis at barrier sites induced by external or internal subverters that either activate the immune system or lower its threshold activation are the major requirement for allergic sensitization. Innate signals produced in the tissue under these conditions equip dendritic cells with a program that shapes an adaptive Th2 response.