Abstract: Objective To clone and express the recombinant amyloid beta-protein(Aβ₄₂) antigen and develop a method for detecting Aβ antibody. Methods Two partially complementary fragments of Aβ₄₂ gene were chemically synthesized for constructing the Aβ₄₂ gene by PCR. The resultant Aβ₄₂ gene fragment was subcloned into pGEX-2T expression vector for inducing the expression of GST-Aβ₄₂ fusion protein, which was purified by affinity chromatography. The antigen specificity and reactivity of the purified GST-Aβ₄₂ fusion protein to Aβ monoclonal antibody were identified with Western blotting. Using either GST-Aβ₄₂ fusion protein or Aβ₄₂ peptide as the coating antigen, an indirect enzyme-linked immunosorbent assay(ELISA) was established for detecting Aβ antibodies in the serum of Aβ₄₂ polypeptide-immunized SD rats. Results GST-Aβ₄₂ fusion protein was successfully expressed as an soluble protein, which, after purification, was found to have a relative molecular mass of 31 kD. About 800 mg of GST-Aβ₄₂ fusion protein were obtained from l L cell culture with a purity over 95%. Western blotting demonstrated specific reaction of this purified GST-Aβ₄₂ fusion protein with Aβ monoclonal antibody. The sensitivity of the indirect ELISA for detecting Aβ antibody was about 2 ng/ml using GST-Aβ₄₂ fusion protein as the coating antigen. There was no significant difference in the results of Aβ antibody detection using either GST-Aβ₄₂ or Aβ₄₂ as the coating antigen(P>0.05). Conclusion GST-Aβ₄₂ fusion protein may serve as a substitute for the expensive Aβ₄₂ peptide for detecting Aβ antibody.