Autoimmune gastritis/ pernicious anaemia

Clinical information

Autoimmune gastritis (AIG) is a chronic inflammation of the mucous membranes that interferes with the absorption of iron and vitamin B12 and can lead to atrophic gastritis with malabsorption. The gastric mucosa is infiltrated by lymphocytes, plasma cells and granulocytes, the epithelial cells are necrotic and the main and parietal cells are replaced by mucoid cells. The final stage is atrophy, which develops over many years. AIG therefore leads to reduced production of pepsin, hydrochloric acid and intrinsic factor (IF). Over the years, the vitamin B12 deficiency develops into pernicious anaemia (PA). In most patients AIG progresses asymptomatically over many years until they reach the advanced stage of atrophy. Symptoms of PA are anaemia, fatigue, drowsiness and tachycardia. Vitamin B12 deficiency also inhibits DNA synthesis, leading to the development of megaloblasts, e. g. in the bone marrow and gastrointestinal epithelium. This results in malabsorption and diarrhoea with weight loss, anorexia, glossitis, jaundice and neurological abnormalities.

Diagnostics

AIG is characterised by the presence of autoantibodies against parietal cell antigens (APCA) and IF. The latter is a glycoprotein that is secreted by parietal cells. IF forms complexes with vitamin B12, the absorption of which in the ileum is impaired by anti-intrinsic factor antibodies (IFA). Sera from AIG and PA patients contain two types of IFA (both IgG): type 1 IFA react with the vitamin B12 binding site of IF, whereas type 2 IFA inhibit the binding of IF to the receptors in the ileum. IFA are characterised by a very high specificity for AIG. In PA, depending on the duration of the disease, IFA occur in 40 % to 80 % of patients.  

APCA can be detected in both AIG and PA patients. They are mainly of the IgG and IgA classes. The prevalence of APCA is very high – close to 100 % – in almost all patients with chronic atrophic gastritis. At the time of diagnosis, APCA also have a very high diagnostic specificity for PA of 80 % to 90 %. As the disease progresses, their prevalence continues to decrease because of the progressive destruction of parietal cells. With regard to the specificity of APCA, it should be noted that they can also be detected in patients with endocrinopathies and in healthy blood donors.  

As a new antigen for the highly specific determination of APCA, EUROIMMUN has developed the recombinant ATP4B antigen. 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 offers significantly improved specificity without loss of sensitivity compared to the Anti-PCA ELISA (IgG). 

Files

Autoimmune gastritis and pernicious anaemia - Differential diagnostics for an insidious disease