**2.2 Intrinsic factor antibodies (IFA)**

Intrinsic factor antibodies are IgG autoantibodies that attack a 60-Kd intrinsic factor glycoprotein secreted by parietal cells that bind to vitamin B-12 and allow for its absorption. There are two types of those autoantibodies, the first is called Type I, which targets cobalamin binding sites and prevents the combination of IF and vitamin B-12. The other type is called Type 2, which targets ileal mucosa receptor and prevents IF-vitamin B-12 complex attachment to it [13, 14]. In addition to H+/K+ ATPase, intrinsic factor (IF) is also a crucial autoantigen in pernicious anemia [15]. IFA have been detected in 13 to 60% of patients with pernicious anemia [16–19] Type I IFA is found to be the predominant type in those cases. While Type II is only found in about half of those cases, Type II IFA is rarely detected in the absence of Type I IFA [14]. IFA has also been associated with autoimmune body gastritis. For instance, Lahner states that intrinsic factor autoantibodies are 100% specific for biopsy-proven autoimmune body gastritis. Moreover, they detected IFA in 27% of patients with ABG and none in healthy controls. Finally, Lahner et al. concluded that testing patients for IFA along with APCA can significantly increase the diagnostic accuracy for atrophic body gastritis and pernicious anemia [20].
