Intrinsic factor

Intrinsic factor is a protein that is produced by the parietal cells of the stomach. It binds to vitamin B12, thereby allowing absorption of the vitamin by intestinal cells. In pernicious anemia, an autoimmune disorder, autoantibodies are formed against intrinsic factor leading to its deficiency. The lack of intrinsic factor then causes malabsorption of vitamin B12 and subsequent anemia. Autoantibodies can also be formed directly against the parietal cells which similarly leads to inadequate intrinsic factor activity and vitamin B12 deficiency. A positive IFAB test result indicates the presence of circulating autoantibodies to intrinsic factor. The combination of megaloblastic anemia, low serum vitamin B12, and the presence of serum IFAB strongly supports the diagnosis of pernicious anemia. Positive IFAB test results are also observed in some patients with other autoimmune disorders such as autoimmune thyroid disease and rheumatoid arthritis. These patients may be at risk for developing pernicious anemia at a later date. The IFAB test is a competitive binding immunoassay employing an antibody that is specific to the B12 binding site on intrinsic factor. A high vitamin B12 concentration in the patient’s serum may interfere with the assay and cause a false-positive result. Thus, a patient receiving a vitamin B12 injection 1 to 2 weeks prior to testing may have a false-positive IFAB result. Conversely, a patient with a previously negative IFAB result may have a positive resul...

Intrinsic factor is a glycoprotein secreted by the gastric mucosa's parietal (human) or chief (rodent) cells. It is important in the absorption of vitamin B 12 (cobalamin) in the intestine in humans, and failure to produce or utilise intrinsic factor results in the condition pernicious anaemia. The action of pepsin and acid in the stomach releases dietary vitamin B 12 from ingested 12 -binding proteins found in the gastric juice present; at low pH, these binding proteins have a higher affinity for the vitamin than intrinsic factor. Pancreatic proteases digest the binding proteins in the small intestine, releasing vitamin B 12 , which then binds to intrinsic factor. Finally, intrinsic factor 12 to be absorbed into portal blood. Vitamin B 12 is required for the maturation of erythrocytes in all mammals, and a lack of this vitamin results in anaemia. Because efficient vitamin B 12 absorption in humans is dependent on intrinsic factor, diseases that reduce intrinsic factor secretion (e.g., atrophic gastritis), interfere with cleavage of the binding proteins (e.g., pancreatic exocrine insufficiency), or decrease binding and absorption of the intrinsic factor-vitamin B 12 complex (e.g., ileal disease or resection) can result in this type of anaemia. A lack of cobalt, a necessary component of vitamin B 12 , can cause anaemia in cattle and sheep, among other symptoms of disease. What is the Function of Castle Intrinsic Factor? The other name for Intrinsic factor (IF) is a gastric ...

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In PA patients, antibodies form and attack either the intrinsic factor (IF), a protein in the stomach needed for the absorption of B12, or the gastric parietal cells, which produce IF in first place. Thus, the two types of pernicious anemia antibodies are the gastric parietal cell antibodies (GPCAs, or just PCAs) and the intrinsic factor antibodies (IFAs). Let’s have a look at both. Parietal Cell Antibodies (PCA) The gastric parietal cells line the wall of our stomach. They specialize in secreting intrinsic factor, and creating gastric acid to help with food digestion. When you digest food, the acid produced by those cells separates the B12 from it. The free B12 then binds to IF to form a unique complex that can now move to the small intestine. When the immune system is producing antibodies to parietal cells (by error, of course), the inevitable destruction of the cells sets in. This results in diminished (or completely absent) gastric acid and IF production, and thus the impaired ability to absorb B12. Since B12 is vital for making red blood cells, anemia soon takes place. Parietal cell antibodies exist in decrease as a result of the progressive loss of parietal cell mass. Only around 55% of people with advanced PA show any anti gastric parietal cell antibodies. Thus, the absence of PCAs doesn’t omit PA. But, if you test positive for these auto gastric parietal cell antibodies, what does it suggest? Not necessarily that you have PA. That’s because PCAs are unspecific to P...