The stomach is exposed to large quantities of foreign proteins daily. Most protein is broken down by stomach acid and digestive enzymes into lessantigenic peptides or is bound by secretory immunoglobulin A (IgA), which prevents it from being absorbed. The epithelial cells lining the stomach do not allow large molecules to pass easily.
For these reasons, less than 2% of the protein in food is absorbed in an allergenic form. The reason food allergies are more prevalent in children is most likely that children have an immature stomach barrier.
When dietary proteins do cross the stomach barrier, the immune system normally suppresses the allergic response. Regulatory T cells, dendritic cells, and local immune responses play critical roles in the development of tolerance. Several types of regulatory T and suppressor cells can all contribute to suppressing allergic responses.
