Journal of Translational Autoimmunity (Dec 2019)
A functional cell-based bioassay for assessing adrenergic autoantibody activity in postural tachycardia syndrome
Abstract
Background: Activating autoantibodies (AAb) to adrenergic receptors (AR) have previously been reported in patients with postural tachycardia syndrome (POTS). These AAb may contribute to a final common pathway for overlapping disease processes, reflecting a possible autoimmune contribution to POTS pathophysiology. In prior studies, measurement of AAb activity was inferred from costly, low-throughput, and laborious physiological assays. In the present study, we developed and validated an alternative cell-based bioassay for measuring AAb activity in serum by means of pre-treatment with monoamine oxidase (MAO). Methods: A total of 37 POTS patients and 61 sex-matched healthy control participants were included. Serum was pre-treated with MAO to remove endogenous catecholamines that could falsely inflate AR activation by AAb. A receptor-transfected cell-based bioassay was used to detect presence of α1AR-AAb and β1AR-AAb in serum. Results: MAO effectively degraded catecholamines as demonstrated by suppression of norepinephrine-induced α1AR activation in POTS (6.4 ± 0.7 vs. 5.5 ± 0.9; P = 0.044) and in controls (4.1 ± 0.5 vs. 3.9 ± 0.6; P = 0.001). Mean activity values were greater in the POTS vs. Controls for α1AR-AAb (6.2 ± 1.2 vs. 5.3 ± 1.0; P < 0.001) and β1AR-AAb (5.7 ± 1.8 vs. 4.1 ± 0.9; P < 0.001). Compared to controls, more POTS patients were positive for α1AR-AAb activity (22% vs 4%; P = 0.007) and β1AR-AAb activity (52% vs. 2%; P < 0.001). Conclusions: The co-presence of norepinephrine in serum samples can artifactually elevate α1AR and β1AR activity, which can be avoided by serum pre-treatment with MAO. Using this novel bioassay, we show that POTS patients have increased α1AR-AAb and β1AR-AAb activity compared to healthy controls in the largest POTS cohort reported to-date. Keywords: Postural tachycardia syndrome, Orthostatic tachycardia, Heart rate, Autoantibody, Adrenergic receptor
