Abstract: Though phase I clinical trial of immunotherapy for Alzheimer’s disease(AD) with inoculated Aβ42 in humans had been proven to be effective, phase II immunotherapy trial was discontinued in 2002 because a few patients developed significant inflammatory reactions caused by C-terminal domain of Aβ42. The aim of the study was to investigate the levels and the abilities of antibodies induced by C-terminal truncated Aβ species to inhibit Aβ42 aggregation and cytotoxity in vitro. 46-week-old male BALB/c mice, Aβ42 and Aβ28/Aβ35/Aβ42 with a C-terminal eight-histidine tag(Aβ28H8, Aβ35H8, and Aβ42H8) were applied in the present study. The mice were randomly divided into 5 groups(n=8), control mice immunized with the normal saline, Aβ42-immunized mice and Aβ42H-/Aβ35H-/Aβ28H-immunized mice. All the serum antibodies were evaluated by measuring their abilities to inhibit Aβ42 aggregation and cytotoxity in vitro. Each mouse was vaccinated with purified Aβ peptide emulsified with Freund’s adjuvant(volume ratio 1:1). Titers, concentrations and isotypes of serum antibodies against Aβ42 were measured by indirect ELISA. Effects of serum antibodies on Aβ42 aggregation and disassembly of Aβ42 fibrils in vitro were observed by electron microscopy. Effects of serum antibodies on Aβ42 cytotoxicity were determined by MTT assay. Aβ42 or Aβ28 could induce higher anti-Aβ42 antibody titer(1:6400) than Aβ35(1:3200). Significantly, Aβ28 induced more IgG1 and IgG2b isotype antibodies and less IgG2b isotype antibody than other Aβ species though all the induced serum antibodies could inhibit Aβ42 aggregation or fibrillogenesis, could induce the disassembly of Aβ42 aggregates, and neutralized or inhibited the cytotoxicity of Aβ42 in vitro. C-Terminal truncated Aβ28 could induce the same effective but safer serum antibodies against Aβ42 than full length Aβ42 by eliciting more Th2-type immune responses.

Key words: Alzheimer’s disease, Amyloid peptide, Antibody, Epitope, Immunization