Intrinsic Factor (IF) is a glycoprotein of the stomach’s parietal cells and it is in charge of binding and transport of vitamin B12.
Intrinsic Factor antibodies (IFA) are highly specific of Pernicious Anemia. Two types of IFA have been described. The first one are the blocking antibodies (type 1) which are directed against the binding site of vitamin B12 to IF and prevent the formation of B12-IF complexes. The second one (type 2), recognize a non-catalytic epitope and may bind indifferently to free Intrinsic Factor molecules or B12-IF complexes.
RadioImmunoAssays (RIA) has been for a long time the reference technique for the detection of anti-IF antibodies, but the Enzyme ImmunoAssays (EIA) are now recognized as more sensitive and specific. In fact RIA uses radio-labelled vitamin B12 in the test as a competitor for the binding of autoantibodies to IF and therefore is only able to detect Type I (blocking) antibodies. Moreover RIA results may be seriously impaired by the interfering presence in the sample of high levels of unlabeled vitamin B12 (e.g. upon treatment of the patient) or B12-transport proteins (e.g. Transcobalamin II) which lead to false positive results. Contrarily EIA methods, which are based on a classical non-competitive detection of IF-bound autoantibodies, are able to detect both type I and type II antibodies (increased sensitivity) and are not influenced by the presence in the serum of unlabeled vitamin B12 or B12-absorbing proteins (increased specificity).
Purified from porcine stomach (for more information on our antigens click here)