The present invention is directed to an immunizing composition containing an antigenic product such as a multiple antigen peptide system (MAPS) or a filamentous bacteriophage displaying an A.beta.PP epitope spanning the .beta.-secretase cleavage site of A.beta.PP and a method for inducing an immune response against the .beta.-secretase cleavage site of A.beta.PP using this immunizing composition. The present invention is also directed to antibodies against the .beta.-secretase cleavage site of A.beta.PP and their use in a method for inhibiting the formation of amyloid .beta..