A Monoclonal Antibody Directed Against an Autoimmune Epitope on the Human 1-Adrenergic Receptor Recognized in Idiopathic Dilated Cardiomyopathy

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 beta(1)-adrenergic receptor (beta(1)AR), 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 10(7) M-1 with an association rate constant (k(on)) of 6.5 x 10(4)M(-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(1)AR of Sf9 cell membranes. Functionally, the MAb was capable of not only reducing the number of the maximal binding sites to the beta(1)-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.