The etiology and the pathogenesis of Alzheimer's disease (AD) have not been clearly delineated. Similarly, the complete molecular composition of the neurofibrillary tangle (NFT) and the amyloid plaque, the pathological hallmarks of AD remain to be determined. During the past several years, evidence has been accumulated to support the thesis that immunological factors may play some role in this disease. We are characterizing the reactive antigens (Ags) detected by monoclonal autoantibodies (auto-Abs) secreted by cell lines established by EBV-transformation of peripheral blood B cells of patients with AD and related disorders. Auto-Abs against beta-amyloid protein (beta-AP) in the amyloid plaques and in vitro have been identified from four cell lines derived from an AD patient (MRE). In addition, it was shown by sequencing the cDNA encoding the V/H and V/L of these auto-Abs that three of them are related because they have identical coding sequences. Thus, they are secreted by B cells from a common progenitor. The corresponding germ line genes of the heavy and light chain V regions have been identified and many nucleotide substitutions have been demonstrated in the cDNA encoding these V regions. The presence of multiple circulating B cells secreting the same auto-Ab and the highly mutated V regions add support to the thesis that the auto-Ab response to beta-AP was an Ag-driven process although it is not certain whether the beta-AP or another Ag with a similar structure is the inciting immunogen.
Specific Aims are 1: To sequence the cDNA encoding for the V/H and V/L of Abs from patient MRE, which are reactive with the beta-AP protein in ELISA but non-reactive with the amyloid plaques in situ. 2: To sequence the cDNA encoding auto-Abs reactive with NFT and other neural structures. 3: To identify a 34kD protein reactive with JGR80 and to document that the protein is over-expressed in AD brain. 4: To determine whether auto-Abs against other epitopes of amyloid precursor protein (APP) which are not present in beta-AP, and against the newly described non APP component of amyloid fibrils are present in supernatants of EBV-transformed B cell lines from AD patients and controls, and to develop the CD-40 system further to culture peripheral blood B cells of AD patients and controls to determine whether the presence of circulating B cells secreting IgG and IgM reactive with beta-AP and other auto-Ag of interest is more prevalent in AD patients. The proposed studies will provide new information regarding the composition of the NFT and the amyloid plaque and insights into the immunological factors in the pathogenesis of AD.
