AUTOANTIBODIES IN PERNICIOUS-ANEMIA TYPE-I PATIENTS RECOGNIZE SEQUENCE 251-256 IN HUMAN INTRINSIC-FACTOR

Pernicious anemia is an organ-specific autoimmune disease characterize d by cobalamin deficiency, megaloblastic anemia, neuropathy, and autoi mmune gastritis with anti-intrinsic factor autoantibodies. Type 1 anti -intrinsic factor autoantibodies block the cobalamin binding site of t he intrinsic factor, a gastric protein required for the assimilation o f cobalamin. The aim of our study was to identify the epitope domain o f type 1 antibodies. Different series of peptides derived from the int rinsic factor sequence were synthesized and tested for antibody bindin g in enzyme-linked immunosorbent assay, radioisotope assay, gel filtra tion, and SDS-PAGE autoradiography. One of these peptides, named IF-R7 (the intrinsic factor aminoacid sequence 251-265), showed a type 1 an tibody binding activity and inhibited, in vitro, their blocking activi ty with Ki at 2.3 mu M. The cross-linking of IF-R7 to beta-lactoglobul in produced type 1 anti-intrinsic factor antibodies in immunized sheep . In vivo Schilling tests performed on guinea pigs also revealed IF-R7 peptide inhibition of type 1 antibody blocking activity. (256)Ser, (2 58)Lys, (262)Tyr and (265)Val Of th, IF-R7 were essential for the epit ope recognition. Reactivity with type 1 antibodies was found in IF-R7 homologous peptides from herpesvirus Saimiri and from pathogenic Esche richia coli. In conclusion, the epitope of type 1 anti-intrinsic facto r autoantibodies is located in the 251-265 amino acid sequence of the protein. The identification of this epitope will enable the definition of an experimental animal model of anti-IF autoimmunity in order to s tudy the pathogenesis of pernicious anemia.