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Autoimmune gastritis (AIG) is a chronic inflammation of the mucous membranes in the fundus and corpus of the stomach. Immune cells attack the oxyntic mucosa, resulting in the destruction of the parietal cells. After an asymptomatic course of many years, AIG can develop into chronic atrophic gastritis, which may manifest as iron deficiency anaemia or pernicious anaemia (PA). The cause of AIG is unknown.
The destruction of the parietal cells leads to hypo- or achlorhydria. However, gastric acid is a necessary factor, especially for the absorption of iron. Young patients in particular therefore often develop iron deficiency anaemia, which cannot be treated by additional oral administration of iron. Due to the progressive loss of parietal cells, the production of intrinsic factor decreases, which is essential for the absorption of B12 in the terminal small intestine. In the long term, this leads to a vitamin B12 deficit and thus to PA. The typical symptoms of anaemia such as fatigue, drowsiness, pale skin and tachycardia are accompanied by diarrhoea, anorexia, glossitis, jaundice and neurological symptoms.
Antibodies against parietal cells (APCA) are considered the most sensitive biomarker for AIG. They can be detected in 80% to 90% of patients. They mainly occur in the early stages of the disease and often several years before the onset of the first symptoms. In advanced gastritis, APCA are less frequently found because the reduction in the number of parietal cells is accompanied by a decrease in the antigen. Due to the fact that APCA are also associated with other autoimmune diseases, e.g. Hashimoto’s thyroiditis, diabetes mellitus type I or coeliac disease, they have limited specificity. For this reason EUROIMMUN has developed the novel recombinant ATP4B antigen for a particularly specific determination of APCA. ATP4B stands for the extracellular domain of the β subunit of H+/ K+ ATPase and is the main antigen of APCA. The Anti-ATP4B ELISA (IgG) thus yields a significantly higher specificity without a loss in sensitivity compared to the Anti-PCA ELISA (IgG). APCA are rarely found in the healthy population, although their prevalence increases with age.
Antibodies against intrinsic factor are highly specific for AIG/PA, although their prevalence is lower than that of APCA. Whereas anti-intrinsic factor antibodies can be detected in the gastric juice of 80% of PA patients, they are only found in the serum of 40% to 60% of patients, increasing to 80% in long-term illness.
EUROIMMUN offers different ELISA, EUROLINE and IIFT test systems for the detection of antibodies against parietal cells, ATP4B and intrinsic factor.