Proteins and the immune system

The ways in which proteins develop and fold give them their structure; some protein structures allow them to resist degradation in the acidic environment of the digestive tract. Others, which might function as cell signal receptors, can be structurally changed by the attachment of other cells. In both cases, the addition of a cell to a protein, its partial degradation, or its survival of the digestive system causes the immune system to tag the cell as foreign and dangerous. This tagging causes an allergic response.[55]