MAbs 3C6, 4B5, and 6E10 exhibit differential binding to amyloidogenic conformers. and 4B5, which preferentially bind assemblies formed from covalent A dimers, but do not bind to amyloid -protein monomer, amyloid precursor protein, or aggregates formed by other amyloidogenic proteins. Monoclonal antibody 3C6, but not an IgM isotype-matched control antibody, ameliorated the plasticity-disrupting effects of A extracted from the aqueous phase of Alzheimers disease brain, thus suggesting that 3C6 targets pathogenically relevant amyloid -protein assemblies. These data prove the usefulness of covalent dimers and their assemblies as immunogens and recommend further investigation of the therapeutic and diagnostic utility of monoclonal antibodies raised to such assemblies. == Introduction == The abnormal accumulation of misfolded, -sheet-rich, protein aggregates is associated with at least 25 disorders (Stefani, 2004;Westermark et al., 2005). Among these maladies, Alzheimers disease (AD) is the most common and because age is a risk factor and life expectancy is constantly increasing, so too Rabbit Polyclonal to XRCC2 are the number of AD cases (Davies et al., 1988;Selkoe, 2001;Ferri et al., 2005;Querfurth and LaFerla, 2010). Pathologically, AD is characterized by the presence of extracellular amyloid plaques, intraneuronal neurofibrillary tangles and synaptic loss throughout the limbic and association cortices (Alzheimer, 1906;Kidd, 1964;Khachaturian, 1985;Hardy and Allsop, 1991;Selkoe, 1991). The amyloid -protein (A) is the primary constituent of amyloid plaques and a Palosuran plethora of genetic, animal modeling and biochemical data indicate that A plays a central role in AD pathogenesis (Walsh and Selkoe, 2007). Numerous studies have shown that water-soluble non-fibrillar A assemblies are toxic and impair disease-relevant models of synaptic form and function (Lambert et al., 1998;Walsh et al., 1999;Walsh et al., 2002;Barghorn et al., 2005;Cleary et al., 2005;Lesne et al., 2006;Lacor et al., 2007;Martins et al., 2008;Shankar et al., 2008;Noguchi et al., 2009). Although, it is not yet known which assembly form(s) of A are the proximate pathogens, recent attention has focused on various forms of A dimers (Shankar et al., 2008;Kok et al., 2009;Sandberg et al., 2010). Highly stable A dimers are specifically found in AD brain and blood (Kuo et al., 1996;Roher et al., 1996;Mc Donald et al., 2010;Villemagne et al., 2010), and brain-derived dimers have been shown to block long-term potentiation Palosuran (LTP), inhibit synapse remodeling, and impair memory consolidation (Klyubin et al., 2008;Shankar et al., 2008;Freir et al., 2011). Moreover, we have recently shown that synthetic A dimers designed to mimic natural dimers can rapidly form meta-stable protofibrils that persist for prolonged Palosuran intervals and potently impair synaptic plasticity (O’Nuallain et al., 2010). Similar structures are also formed by A monomer, but the amount formed and the time over which they exist is dramatically extended for Palosuran dimer, thus suggesting that A dimers aggregate by a process distinct from monomer. A large number of studies have demonstrated that both the active generation or passive transfer of anti-A antibodies can prevent or reverse A-induced cognitive impairment in APP transgenic mice (Games et al., 2006) and this has prompted several clinical trials in humans (Schenk, 2002;Gilman et al., 2005). Most forms of immunotherapy employ antibodies that recognize multiple different assembly forms of A, including monomer. This approach suffers from the loss of antibody capacity due to binding to non-pathogenic forms of A and removal of Palosuran useful A (Arancio and Chao, 2007;Puzzo et al., 2008). An alternate approach would be to develop antibodies that specifically recognize pathogenic forms of A dimers and ameliorate their toxic activity. To address this we used a preparation of covalently stabilized A (140)Cys26 dimers free of A monomer or fibrils as an immunogen and screened hybridomas for their ability to produce antibodies that discriminate between reduced non-cross-linked monomer and covalently linked dimers. Two murine mAbs IgMs, referred to as 3C6 and 4B5, preferentially bind covalent A dimer assemblies, but not A monomer or fibrils formed by other amyloidogenic proteins. Notably, mAb 3C6, but not.