A monoclonal antibody directed against an autoimmune epitope on the human beta 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 h uman beta(1)-adrenergic receptor (beta(1)AR), against which functional auto antibodies have been detected in patients with idiopathic dilated cardiomyo pathy, The MAb was found to be of IgG2b type and directed against a conform ational epitope, encompassing the sequence recognized by the human autoanti bodies. 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 immun oprecipitated only poorly the solubilized beta(1)AR of Sf9 cell membranes. Functionally, the MAb was capable of not only reducing the number of the ma ximal binding sites to the beta(1)-adrenergic receptor of transfected Sf9 c ell membranes, but also of displaying a positive chronotropic effect on cul tured neonatal rat cardiomyocytes, These properties, which the MAb shares w ith the human autoantibodies, makes it an interesting tool for passive tran sfer studies in mice.