Journal ofNeurotmmunology, 48 (1993) 199-204 199 © 1993 Elsevier Science Publishers B.V. AII rights reserved 0165-5728/93/$06.00 JNI 02468 Binding of IgG to amyloid/3A4 peptide via the heavy-chain hinge region with preservation of antigen binding David Huang a, Margaret Martin b, Danny Hu c, Allen D. Roses a,b, Dmitry Goldgaber d and Warren J. Strittmatter *'a'b a Department of Neurobiology, Duke Unwersity Medical Center, Durham, NC 27710, USA b Department of Medicine (Neurology) Box 2900, Joseph and Kathleen Bryan Neurobiology Buildmg, Duke University Medical Center, Durham, NC 27710, USA c Duke Untversity, Durham, NC 27710, USA d Department of Psychiatry and Behavioural Science, State University of New York at Stony Brook, NYl1794-8101, USA (Received 5 April 1993) (Revision received 30 June 1993) (Accepted 1 July 1993) Key words: Alzheimer's Disease; IgG; Senile plaque; /3A4 amyloid peptide Summary Amyloid /3A4 peptide is found in the extracellular region of the senile plaque and in the angiopathy of Alzheimer's disease. Several other proteins, including IgG, also reside in these abnormal structures. In an attempt to understand how these structures are assembled and to determine how proteins are recruited, interactions of various proteins with synthetic /3A4 peptide have been examined in vitro. Purified IgG binds directly to synthetic /3A4 peptide with high avidity. The domain between amino acids 12-28 of/3A4 binds IgG. /3A4 peptide binds the hinge region of the immunoglobulin heavy chain, and preserves the ability of the immunoglobulin to bind antigen. A protein which does not bind directly to/3A4 peptide can be targetted to the senile plaque and angiopathy by binding to IgG, which avidly binds/3A4 peptide. Introduction The senile plaque and congophilic angiopathy are abundant lesions in the brains of patients with Alzheimer's disease (Selkoe, 1991). They both contain complex extracellular structures whose biochemical composition and mechanism of assembly have been characterized only partially. Their role in the patho- genesis of the disease is not known. A prominent constituent of the senile plaque and angiopathy is amyloid /3A4 peptide. /3A4 peptide is produced by proteolytic processing of the amyloid precursor protein (APP) (Younkin, 1991), and contains 39-43 amino acids. Several additional proteins have been localized to the plaque and angiopathy, including apolipoprotein E (Namba et al., 1991; Wisniewski et al., 1992; * Corresponding author. Phone (919) 684 5963, Fax (919) 684 6514. Strittmatter et al., 1993a), a-l-antichymotrypsin (Abraham et al., 1988), complement factors Clq and C3q (Eikelenboom et al., 1982; McGeer, 1989), APP (Beyreuther et al., 1991) and lgG (Ishii et al., 1975, 1976; Ihara et al., 1981). The functional interactions of plaque proteins in either the pathogenesis of the dis- ease or in the response to the disease are not known. Alternatively the presence of IgG in senile plaques could result from extravasation post mortem. To study the binding of proteins to the /3A4 peptide we devel- oped an in vitro assay in which synthetic /3A4 peptide is covalently immobilized to a membrane matrix (Strit- tmatter et al., 1993a). Using this assay we have previ- ously characterized the binding of apolipoprotein E and amyloid precursor protein to synthetic /3A4 pep- tide (Strittmatter et al., 1993a,b). Here we demonstrate that IgG directly and avidly binds synthetic /3A4 amy- loid, resisting dissociation by either sodium dodecyl sulfate or guanidine hydrochloride. Binding of the IgG heavy chain to /3A4 peptide occurs through the IgG