RECEPTOR-SPECIFIC FUNCTIONAL-PROPERTIES OF BETA(2)-ADRENERGIC RECEPTOR AUTOANTIBODIES IN ASTHMA

beta(2)-Adrenergic receptor (beta(2)AR) autoantibodies have been reported in the serum from subjects with asthma but the functional significance of such antibodies is not known, To characterize these antibodies, we developed a Western blot (WE) technique that utilized overexpressed recombinant human beta(2)AR as antigen and also developed a control antisera in rabbits directed against the C-terminus of the receptor. beta(2)AR autoantibodies were detected in similar to 5% of normal subjects and in similar to 40% of asthmatic subjects. Eighty-four percent of these antibodies were of the IgG class, with the remainder being IgM. Most (73%) of WE-positive sera inhibited [I-125]cyanopindolol binding to recombinant solubilized receptors. The mean binding inhibition was 40.4 +/- 5.1% for WE-positive sera versus 7.6 +/- 1.2% for WB-negative sera, Binding of antibody to beta(2)AR expressed on intact cells significantly depressed receptor function, with a > 50% attenuation of isoproterenol-stimulated cAMP production. This effect was receptor specific, as forskolin-stimulated cAMP accumulation was not affected by exposure to sera, WE-positive sera that did not inhibit radioligand binding had no effect on receptor function, Thus, some antibodies appear to bind near the ligand binding pocket and act as functional antagonists. In addition, incubation of intact cells expressing beta(2)AR with WB-positive sera for 18 h resulted in a 30.3 +/- 0.6% downregulation of receptor number, whereas WE-negative sera induced no downregulation. This downregulation response with WB-positive sera was not affected by coincubation with the antagonist propranolol and was apparently not dependent upon whether the antibody interacted with ligand binding pocket. Thus, autoantibodies to beta(2)AR in the serum of asthmatic subjects are directed to an extracellular or transmembrane spanning domain of the protein and can act to antagonize functional activation of the receptor by agonist and/or to downregulate receptor expression, These beta(2)AR antibodies share certain properties with autoantibodies against other types of receptors such as those found in myasthenia gravis and insulin resistance.