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

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 Aβ₁₋₄₂-coated biopanning. B6 bound to fibrillar Aβ₁₋₄₂ as well as globulomer Aβ₁₋₄₂ but not to soluble Aβ₁₋₄₂ or Aβ₁₋₄₀. B6 inhibited Aβ₁₋₄₂ 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 Aβ₁₋₄₂. Although it is believed that N-terminus-recognizing antibodies tend to show the capability to inhibit Aβ₁₋₄₂ fibrillation, B6 is the first human inhibitory antibody recognizing the C-terminus of Aβ₁₋₄₂.