Abstract 215: An Agonistic Human Monoclonal Autoantibody to the β2-adrenergic Receptor: Implications in Postural Hypotension
Functional autoantibodies directed to the autonomic receptors have been increasingly recognized to contribute to the pathophysiology of various cardiovascular diseases. However, to date, no human monoclonal autoantibodies to these receptors with agonist activity have been available. We have recently reported a subgroup of patients with idiopathic postural hypotension who have no known etiology are associated with vasodilatory autoantibodies to the β2-adrenergic receptor (β2AR). Using standard hybridoma techniques, we produced a β2AR-activating monoclonal autoantibody C5F2 from the peripheral blood lymphocytes of a patient with idiopathic postural hypotension and high ELISA antibody titers to a peptide corresponding to the second extracellular loop (ECL2) of β2AR. C5F2 was of the IgG3 isotype and recognized an epitope located at the N-terminus of β2AR ECL2 as determined by epitope mapping using multipin peptide synthesis. Confocal immunofluorescence revealed C5F2 binding to the β2AR in Chinese hamster ovary (CHO) cells transfected with human β2AR and rat cremaster arterioles, both of which were inhibited by presabsorption with the β2AR ECL2 peptide. Functionally, the C5F2 IgG stimulated cyclic AMP production in β2AR-expressing CHO cells in a dose-dependent manner (0.005-5 mg/ml). C5F2-induced cyclic AMP activation was specifically blocked by both the β2AR ECL2 peptide and β2AR selective antagonist ICI-118551. In an isolated rat cremaster arteriole assay, infusion of the C5F2 IgG produced a potent vasodilation which was inhibited by the β2AR ECL2 peptide and β2AR blocker ICI-118551 (from 67.8±5.8% to 9.3±5.1% and 4.4±2.1% of maximal dilatory response, respectively), indicating that antibody activation of vascular β2AR may contribute to systemic vasodilation. These data support the concept that circulating agonistic autoantibodies serve as vasodilators and may cause or exacerbate orthostasis by altering the compensatory postural vascular response. The availability of this first human monoclonal autoantibody to the β2AR provides opportunities to identify previously unrecognized causes and new pharmacological management of postural hypotension.
- © 2012 by American Heart Association, Inc.