A Monoclonal Antibody Directed Against an Autoimmune Epitope on the Human β1-Adrenergic Receptor Recognized in Idiopathic Dilated Cardiomyopathy

Abstract

A monoclonal antibody (MAb M16) was obtained by immunizing Balb/C mice with free peptide H26R, corresponding to the second extracellular loop of the human β₁-adrenergic receptor (β₁AR), against which functional autoantibodies have been detected in patients with idiopathic dilated cardiomyopathy. The MAb was found to be of IgG2b type and directed against a conformational epitope, encompassing the sequence recognized by the human autoantibodies. BIAcore measurements yielded an equilibrium constant of 6.5 X 10⁷ M¹ with an association rate constant (k_on) of 6.5 X 10⁴M^-1 sec^-1 and a dissociation rate constant (k_off) of 1.0 X 10^-3 sec^-1. It immunoprecipitated only poorly the solubilized beta ₁AR of Sf9 cell membranes. Functionally, the MAb was capable of not only reducing the number of the maximal binding sites to the β₁-adrenergic receptor of transfected Sf9 cell membranes, but also of displaying a positive chronotropic effect on cultured neonatal rat cardiomyocytes. These properties, which the MAb shares with the human autoantibodies, makes it an interesting tool for passive transfer studies in mice.