People with celiac disease (gluten-sensitive enteropathy) must avoid eating wheat, rye, and barley storage proteins in order to avoid adverse changes to their intestinal mucosa that can lead to serious malabsorption of almost all nutrients (Kasarda 2000 Feighery 1999 Maki and Collin 1997 Wieser 1995). The wheat, rye, and barley storage proteins are collectively called gluten proteins by celiac patients and their physicians, although, strictly speaking, gluten is derived only from the endosperm of wheat grain.
Both celiac disease and allergy can be triggered by gluten proteins although these responses involve different immunological mechanisms. Celiac disease is sometimes classified as a Type IV hypersensitivity mediated by T-cell responses whereas allergy is usually classed as a Type I hypersensitivity mediated by E-type immunoglobulins (IgE antibodies). In a very broad sense of `disease following a response by the immune system to an otherwise innocuous antigen,` however, both celiac disease and allergy could be accommodated under the definition of allergy (Janeway et al. 1999), but limitation of the term allergy to Type I hypersensitivy is the current, more usual practice.