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 (WB) technique that utilized overexpressed recombinant human beta 2AR as antigen and also developed a control antisera in rabbits directed against the C-terminus of the receptor. beta 2AR autoantibodies were detected in approximately 5% of normal subjects and in approximately 40% of asthmatic subjects. Eighty-four percent of these antibodies were of the IgG class, with the remainder being IgM. Most (73%) of WB-positive sera inhibited [125I]cyanopindolol binding to recombinant solubilized receptors. The mean binding inhibition was 40.4 +/- 5.1% for WB-positive sera versus 7.6 +/- 1.2% for WB-negative sera. Binding of antibody to beta 2AR 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. WB-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 2AR with WB-positive sera for 18 h resulted in a 30.3 +/- 0.6% downregulation of receptor number, whereas WB-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.(ABSTRACT TRUNCATED AT 250 WORDS)
Turki
J
J
Department of Medicine (Pulmonary), University of Cincinnati College of Medicine, Ohio, USA.
Liggett
S B
SB
D000937:Antigen-Antibody Reactions; D001249:Asthma / Q000276:immunology*; D001323:Autoantibodies / Q000276:immunology*; D015153:Blotting, Western / Q000379:methods; D000242:Cyclic AMP / Q000378:metabolism; D015536:Down-Regulation; D006801:Humans; D011487:Protein Conformation; D011943:Receptors, Adrenergic, beta / Q000276:immunology*; D011994:Recombinant Proteins; D015398:Signal Transduction
D001323:Autoantibodies; D011943:Receptors, Adrenergic, beta; D011994:Recombinant Proteins; D000242:Cyclic AMP