A peptide having an ED50 of less than 500 nm, in particular 10 nM to an antibody which recognizes an epitope on an extracellular α1 loop 2 or β2 loop 1 of a human adrenoceptor wherein the antibody's binding to the epitope results in an increase of γ-secretase activity, an increased release of β-amyolid molecules and/or cellular dysfunction of cerebral blood vessel cells, glia cells or neurons, wherein the ED50 value is measured by bioassay.