#$%^&*AU2016208334A120160811.pdf#####ABSTRACT A novel constrained peptide epitope derived from AP, related antibody compositions and methods of use. An isolated antibody that specifically binds to a cyclic peptide comprising the conformational epitope corresponding to a solvent-exposed, antibody accessible knuckle region of oligomeric As is described. An antigenic peptide comprising an epitope having a constrained cyclic configuration, corresponding to a solvent-exposed, antibody accessible knuckle region of oligomeric A is also described. Methods of treating, preventing, and diagnosing Alzheimers disease are also described.