Optimal TH2A effector function requires local epithelial cytokine signaling

Allergen-reactive TH2A cells are identified as a pathogenic subpopulation in allergic inflammation. We hypothesized TH2A cells would confer susceptibility to the effects of the epithelial cytokine IL-33 due to selective expression of the IL-33 receptor ST2. We sought to determine whether expression of the IL-33 receptor ST2 was unique to TH2A cells and to determine the role of IL-33 in modulating human allergen-specific T cell responses. We recruited seasonal (pollen), perennial (dust mite), or food (peanut) allergic individuals on the basis of clinical history and serum IgE > 0.35 kU/L. Allergen-reactive CD4+ T cells were tracked using the CD154 assay following short-term stimulation with either peanut, pollen or house dust mite allergen crude extract in the presence or absence of IL-33. The CD154+ cells were stained with various combinations of surface marker antibodies for phenotyping using flow cytometry. Cytokine profiles were determined using intracellular staining. Total TH2A (CD4+CRTH2+CD27-CD161+) and type 2 innate lymphoid cells (Lineage-CD127+CRTH2+CD161+) were used as control populations. We found that ST2 expression within allergen-specific T cells is restricted to allergic patients and is most highly expressed in the TH2A subset. This phenomenon appears to be consistent in our seasonal, perennial, and food allergy models. Although not completely absent from resting TH2A cells, ST2 expression is lower in these cells suggesting TCR-triggering is needed for ST2 expression. Our data reveals that IL-33 selectively amplifies allergen specific TH2A cell responses, increasing IL-4 and IL-5 pro-inflammatory cytokine levels following activation. Overall, we have found core similarities between TH2A cells and ILC2s, notably that both cell types are capable of sensing locally elicited tissue cytokines. However, TH2A cells require TCR stimulation to upregulate ST2 expression whereas IL-33 alone is sufficient to activate ILC2s Like ILC2s, activated allergen-specific TH2 cells are capable of sensing locally elicited tissue cytokines suggesting a checkpoint that regulates both innate and adaptive allergic immunity. Our findings validate the strategy of blockade of tissue signals for treating allergic disease during allergen-specific immunotherapy.