Autoantibodies in pernicious anemia type I patients recognize sequence 251-256 in human intrinsic factor.
Pernicious anemia is an organ-specific autoimmune disease characterized by cobalamin deficiency, megaloblastic anemia, neuropathy, and autoimmune gastritis with anti-intrinsic factor autoantibodies. Type 1 anti-intrinsic factor autoantibodies block the cobalamin binding site of the intrinsic factor, a gastric protein required for the assimilation of cobalamin. The aim of our study was to identify the epitope domain of type 1 antibodies. Different series of peptides derived from the intrinsic factor sequence were synthesized and tested for antibody binding in enzyme-linked immunosorbent assay, radioisotope assay, gel filtration, and SDS-PAGE autoradiography. One of these peptides, named IF-R7 (the intrinsic factor aminoacid sequence 251-265), showed a type 1 antibody binding activity and inhibited, in vitro, their blocking activity with Ki at 2.3 microM. The cross-linking of IF-R7 to beta-lactoglobulin 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. 256Ser, 258Lys, 262Tyr and 265Val of the IF-R7 were essential for the epitope recognition. Reactivity with type 1 antibodies was found in IF-R7 homologous peptides from herpesvirus Saimiri and from pathogenic Escherichia coli. In conclusion, the epitope of type 1 anti-intrinsic factor 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 study the pathogenesis of pernicious anemia.
Guéant
J L
JL
Department of Gastroenterology, Faculty of Medicine, Henri Poincaré University, Vandoeuvre-lès-Nancy, France.
Safi
A
A
Aimone-Gastin
I
I
Rabesona
H
H
Bronowicki
J P
JP
Plénat
F
F
Bigard
M A
MA
Haertlé
T
T
D000595:Amino Acid Sequence; D000752:Anemia, Pernicious / Q000145:classification / Q000276:immunology*; D000818:Animals; D000918:Antibody Specificity; D001323:Autoantibodies / Q000097:blood*; D001327:Autoimmune Diseases / Q000145:classification / Q000276:immunology*; D001667:Binding, Competitive; D000939:Epitopes / Q000276:immunology; D006168:Guinea Pigs; D006801:Humans; D007437:Intrinsic Factor / Q000276:immunology*; D008969:Molecular Sequence Data; D009842:Oligopeptides / Q000138:chemical synthesis / Q000276:immunology; D010446:Peptide Fragments / Q000138:chemical synthesis / Q000276:immunology; D011863:Radioimmunoassay; D012546:Schilling Test; D012756:Sheep; D014805:Vitamin B 12 / Q000378:metabolism
D001323:Autoantibodies; D000939:Epitopes; D009842:Oligopeptides; D010446:Peptide Fragments; D007437:Intrinsic Factor; D014805:Vitamin B 12