We investigated the therapeutic effects of two different versions of A␤ 1-15 (16) liposome-based vaccines. Inoculation of APP-V717IxPS-1 (APPxPS-1) double-transgenic mice with tetrapalmitoylated amyloid 1-15 peptide (palmA␤ 1-15), or with amyloid 1-16 peptide (PEG-A␤ 1-16) linked to a polyethyleneglycol spacer at each end, and embedded within a liposome membrane, elicited fast immune responses with identical binding epitopes. PalmA␤ 1-15 liposomal vaccine elicited an immune response that restored the memory defect of the mice, whereas that of PEG-A␤ 1-16 had no such effect. Immunoglobulins that were generated were predominantly of the IgG class with palmA␤ 1-15, whereas those elicited by PEG-A␤ 1-16 were primarily of the IgM class. The IgG subclasses of the antibodies generated by both vaccines were mostly IgG2b indicating noninflammatory Th2 isotype. CD and NMR revealed predominantly ␤-sheet conformation of palmA␤1-15 and random coil of PEG-A␤ 1-16. We conclude that the association with liposomes induced a variation of the immunogenic structures and thereby different immunogenicities. This finding supports the hypothesis that Alzheimer's disease is a ''conformational'' disease, implying that antibodies against amyloid sequences in the ␤-sheet conformation are preferred as potential therapeutic agents.Alzheimer's disease ͉ ␤-amyloid ͉ vaccine C linical manifestations of Alzheimer's disease (AD) include progressive memory loss, cognitive impairment, confusion, and personality changes. The major neuropathological changes in the brains of AD patients are senile plaques and neurofibrillar tangles causing progressive neuronal dysfunction. These pathological alterations are likely causally involved in eventual neuronal death, particularly in brain regions related to memory and cognition (1-4). Senile plaques are formed predominantly by the ␤-amyloid peptide A␤ 1-42 that is coiled and ␣-helical in its soluble form but, upon conformational transition, aggregates into ␤-sheeted multimers. The monomeric A␤ peptide is a physiological metabolite of the large amyloid precursor protein (APP, 695-770 aa) that undergoes processing by several sequential proteolytic steps (5). The A␤ 1-42 aggregates are proposed to play the key role in the pathogenesis of AD (6). In transgenic animals that overexpress mutant human APP, anti-A␤-specific antibodies decreased the A␤ burden and improved memory after either passive (7-11) or active (12-18) immunization.We previously demonstrated that i.p. inoculation of tetrapalmitoylated A␤1-16 reconstituted in liposomes to transgenic NORBA mice elicited significant titers of anti-A␤ antibodies, that solubilized amyloid fibers in vitro and pancreatic A␤ plaques in vivo (19). To circumvent T cell-mediated immune responses known to be causatively involved in the adverse events of meningoencephalitis of AD patients immunized with A␤1-42 (20-22), the A␤1-16 and 1-15 sequences were used for immunization of APPxPS1 double-transgenic mice (23) because strong T cell epitopes are located more toward the C-te...

Viroids are single-stranded, circular RNAs of 250 to 400 bases, that replicate autonomously in their host plants but do not code for a protein. Viroids of the family Pospiviroidae, of which potato spindle tuber viroid (PSTVd) is the type strain, are replicated by the host's DNA-dependent RNA polymerase II in the nucleus. To analyze the initiation site of transcription from the (+)-stranded circles into (-)-stranded replication intermediates, we used a nuclear extract from a non-infected cell culture of the host plant S. tuberosum. The (-)-strands, which were de novo-synthesized in the extract upon addition of circular (+)-PSTVd, were purified by affinity chromatography. This purification avoided contamination by host nucleic acids that had resulted in a misassignment of the start site in an earlier study. Primer-extension analysis of the de novo-synthesized (-)-strands revealed a single start site located in the hairpin loop of the left terminal region in circular PSTVd's secondary structure. This start site is supported further by analysis of the infectivity and replication behavior of site-directed mutants in planta.