Immunoreactivity of Phage Library-derived Human Single-Chain Antibodies to Amyloid Beta Conformers In Vitro

摘要

The pathogenesis of Alzheimer's disease involves conformational changes of Aβ. A series of antibodies recognizing a distinct conformation of Aβ (snapshot antibody) is useful for both understanding the mechanism of molecular conversion and identifying diagnostic and therapeutic reagents. As Aβ with various conformations can be prepared in vitro under varying physicochemical conditions, snapshot antibodies can be isolated by directly binding to target molecules with antibody-displaying phages. We tested the feasibility of this idea. We show a feature of several Aβ-reactive antibodies isolated from our human single-chain Fv antibody-phage library and particularly report the characteristics of an scFv clone, B6, selected from the fibrillar Aβ_1–42-coated biopanning. B6 bound to fibrillar Aβ_1–42 as well as globulomer Aβ_1–42 but not to soluble Aβ_1–42 or Aβ_1–40. B6 inhibited Aβ_1–42 fibril formation with 600 nM IC₅₀ in spite of being the monovalent scFv form. Epitope analysis suggested that the binding site might be located at the β2 sheet of the C-terminus of Aβ_1–42. Although it is believed that N-terminus-recognizing antibodies tend to show the capability to inhibit Aβ_1–42 fibrillation, B6 is the first human inhibitory antibody recognizing the C-terminus of Aβ_1–42.