Discovery and characterization of dietary antigens in oral tolerance.

Food antigens elicit immune tolerance through the action of regulatory T cells (Tregs) in the intestine. Although antigens that trigger common food allergies are known, the epitopes that mediate tolerance to most foods have not been described. Here, we identified murine T cell receptors specific for maize, wheat, and soy, and used expression cloning to de-orphan their cognate epitopes. All of the epitopes derive from seed storage proteins that are resistant to degradation and abundant in the edible portion of the plant. Multiple unrelated T cell clones were specific for an epitope at the C-terminus of 19 kDa alpha-zein, a protein from maize kernel. An MHC tetramer loaded with this antigen revealed that zein-specific T cells are predominantly Tregs localized to the intestine. These cells, which develop concurrently with weaning, constitute up to 2% of the peripheral Treg pool. Bulk and single-cell RNA sequencing revealed that these cells express higher levels of immunosuppressive markers and chemokines compared to other Tregs. These data suggest that immune tolerance to plant-derived foods is focused on a specific class of antigens with common features, and they reveal the functional properties of naturally occurring food-specific Tregs.