Studies on Antibody to Intrinsic Factor *

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Abstract
Sera from a group of 79 patients with pernicious anemia were studied for the presence of antibody to intrinsic factor. Two general types of antibody activity were found, and it was possible to distinguish three groups of pernicious anemia sera on the basis of their content of these types. Type I antibody blocks the binding of radioactive vitamin B12 to intrinsic factor when added to intrinsic factor before the B12; it is not detected on intrinsic factor when added after B12. This antibody blocks intrinsic factor-mediated B12 absorption in vivo when mixed in the sequence intrinsic factor + antibody I + B12, but not when mixed in the sequence intrinsic factor + B12 + antibody I. Type II antibody reacts with intrinsic factor when B12 is attached. This antibody prevents the absorption of B12 from intrinsic factor in pernicious anemia patients when mixed in the sequence intrinsic factor + B12 + antibody II, and is thereby distinguished from antibody I.