Profile Of Food Allergen-Specific T Cells In Allergic and Clinically Tolerant Individuals

The interplay between antigen-specific T-effector and T-regulatory cells in food allergy and tolerance is poorly understood in humans. Using blood from children allergic to peanut and/or egg versus clinically tolerant controls (including healthy, outgrown food allergy, or allergic to other foods), we designed 13-color flow cytometry panels to profile peanut or egg-specific T cell responses 6-18h after stimulation. Antigen-specific cells were identified as live/CD3+/CD4+/CD40L+, and profiled for regulatory markers (CD25/CD127/Foxp3), cytokines (IL-4/IL-13/IL-10/IFN-g), and homing markers (CCR6/CCR4/CXCR5/CCR9). Allergic subjects had detectable peanut-responsive CD40L+ T cells above background (median 206 per million CD4 vs. 37 at 6h and 408 vs 56 at 18h, n=20 and 13, p<0.0001 and p=0.0002). In healthy controls, there were few detectable peanut-responsive cells above background at 6hrs (84 vs. 66, n=3). Similar responses were observed in egg-stimulated samples from children allergic (n=13) or clinically tolerant (n=6) to egg. Egg and peanut-specific T cells in allergic subjects co-expressed IL-4 and IL-13, but little or no IFNg or IL-10. In control subjects TH2 cytokine expression was absent with minimal IFN-g or IL-10. Antigen-specific “Tregs”, defined as CD40L+/CD25+/CD127-/FoxP3+, were significantly increased beginning 18h after allergen stimulation, were present in both allergic and tolerant individuals, and were enriched for skin-homing (CCR4) and mucosal-homing (CCR6) receptor expression. Antigen-specific “Tregs” with tissue homing phenotypes are detectable in both allergic and tolerant subjects, while antigen-specific Th2-effector cells are unique to allergic individuals. These results suggest that food allergy is not due to a quantitative deficiency in allergen-specific Tregs; regulatory function remains to be addressed.