Am. J. Respir. Cell Mol. Biol., Vol 12, No. 5, May 1995, 531-539.
Receptor-specific functional properties of beta 2-adrenergic receptor autoantibodies in asthma
J Turki and SB Liggett
Department of Medicine (Pulmonary), University of Cincinnati College of Medicine, Ohio, USA.
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)
