Anti-gliadin antibodies

Anti-gliadin antibodies are produced in response to gliadin, a prolamin found in the wheat. In bread wheat it is encoded by three different genomes, AA, BB, and DD. These genomes can produce slight different gliadins, which can cause the body to produce different antibodies. Some of these antibodies can detect proteins in specific grass taxa such as Triticeae (Triticeae glutens), while others react sporadically across with certain species in those taxa, or over many taxonomically defined grass tribes.

Anti-gliadin IgA
This antibody is found in ~80% of patients with Coeliac Disease. It is directed against the alpha/beta and gamma (α,β,γ) gliadins. It is also found in a number of patients who are not enteropathic. Some of these patients may have neuropathies that respond favorably to gluten elimination diet. This is referred to as gluten-sensitive idiopathic neuropathy. Clinically these antibodies and IgG antibodies to gliadin are abbreviated as AGA.

Anti-gliadin IgG
IgG antibodies is similar to AGA IgA, but is found at higher levels in patients with the IgA-less phenotype. It is also associated with coeliac disease and Idiopathic gluten sensitivity. and IgA-less is associated with Coeliac disease. Anti-gliadin antibodies are frequently found with anti-transglutaminase antibodies

Anti-gliadin IgE
The IgE antibodies are more typically found in allergy-related conditions such as urticaria, asthma, and wheat-dependent exercise-induced anaphylaxis. The target of the most allergenic antibodies are ω-5 gliadin, that is encoded by the Gli-1B gene found on the B haplome (Aegilops speltoides derived) of wheat.

Anti-gliadin antibodies and the gluten-free diet
What is the relationship of gluten and anti-gliadin antibodies?. In gluten-sensitive individuals AGA testing is a routinely used blood test for possible presence of coeliac disease, allergies or idiopathic phenomena. The measurement of AGA is done with ELISA or radioimmunoassay. Such test measure the level of AGA relative to a standard, such as a level of 10 = point in which 85% of normal population falls below. Greater than 10 equals disease and a value of 3 is expected (mean).

Individuals who have coeliac disease may have values in excess of 200. There is the common expectation that removal of gluten results in the loss of AGA, however since gluten is the target of the antibodies, that which would deplete them from the body, removal of gluten results in the benign circulation of antibodies. The half life of these antibodies is typically 120 days. Given an expected normal of 3 and assuming that the individual starts with a score of 203 we can predict the levels of AGA at various future time points. Based on these initial numbers, patients with very high AGA values may take 2 years to return to the normal range.

Refractory coeliac diease (RCD). RCD or non-strict gluten-free diet can be two cause of failure of AGA to return to normality on the GF diet. The first instance lymphocytes may remain stimulated even though the antigen that originally stimulated them was removed from the diet.

Diagnostic serology
Anti-gliadin antibodies were one of the first serological markers for coeliac disease. Problematic with AGA is the typical sensitivity and specificity was about 85%. Gliadin peptides which are senthesized as the deamidated form have much higher sensitivity and specificity, creating 2 serological tests for CD that approach biopsy diagnostic in performance.