The present invention provides a recombinant immunogenic obtained by tandem multimerization of a B-cell epitope bearing fragment of A.beta.42, within the active loop site of a carrier (display site), preferably bacterial thioredoxin (Yrx). Polypeptides bearing multiple copies of A.beta.42 fragments, preferably with an interposed amino acid linker, were constructed and injected into mice in combination with an adjuvant. Elicited antibodies were found to selectively bind to fibrillar and/or oligomers A.beta. within neuritic AD plaques.