Functional autoantibodies against G-protein coupled receptors in patients with persistent Long-COVID-19 symptoms

Abstract

Impairment of health after overcoming the acute phase of COVID-19 is being observed more and more frequently. Here different symptoms of neurological and/or cardiological origin have been reported. With symptoms, which are very similar to the ones reported but are not caused by SARS-CoV-2, the occurrence of functionally active autoantibodies (_fAABs) targeting G-protein coupled receptors (GPCR-_fAABs) has been discussed to be involved. We, therefore investigated, whether GPCR-_fAABs are detectable in 31 patients suffering from different Long-COVID-19 symptoms after recovery from the acute phase of the disease. The spectrum of symptoms was mostly of neurological origin (29/31 patients), including post-COVID-19 fatigue, alopecia, attention deficit, tremor and others. Combined neurological and cardiovascular disorders were reported in 17 of the 31 patients. Two recovered COVID-19 patients were free of follow-up symptoms. All 31 former COVID-19 patients had between 2 and 7 different GPCR-_fAABs that acted as receptor agonists. Some of those GPCR-_fAABs activate their target receptors which cause a positive chronotropic effect in neonatal rat cardiomyocytes, the read-out in the test system for their detection (bioassay for GPCR-_fAAB detection). Other GPCR-_fAABs, in opposite, cause a negative chronotropic effect on those cells. The positive chronotropic GPCR-_fAABs identified in the blood of Long-COVID patients targeted the β₂-adrenoceptor (β₂-_fAAB), the α₁-adrenoceptor (α₁-_fAAB), the angiotensin II AT1-receptor (AT1-_fAAB), and the nociceptin-like opioid receptor (NOC-_fAAB). The negative chronotropic GPCR-_fAABs identified targeted the muscarinic M₂-receptor (M₂-_fAAB), the MAS-receptor (MAS-_fAAB), and the ETA-receptor (ETA-_fAAB). It was analysed which of the extracellular receptor loops was targeted by the autoantibodies.

Keywords: ACE2, Angiotensin-converting enzyme 2 receptors; AT1-fAAB, Autoantibody targeting the angiotensin II AT1 receptor; Autoantibody; Autoimmunity; COVID-19; CRPS, Complex regional pain syndrome; ETA-fAAB, Autoantibody targeting the endothelin receptor; Fatigue; GPCR, G-protein coupled receptors; Long-COVID; M2-fAAB, Autoantibody targeting the muscarinic receptor; MAS-fAAB, Autoantibody targeting the MAS receptor; NOC-fAAB, Functionally active autoantibody against the nociceptin receptor; PoTS, Postural orthostatic tachycardia syndrome; Post-covid-19 symptom; RAS, Renin angiotensin system; SARS, Severe acute respiratory syndrome; fAAB, Functional autoantibody; α1-fAAB, Autoantibody targeting the alpha1-adrenoceptor; β2-fAAB, Autoantibody targeting the beta2-adrenoceptor.

Fig. 1

Loop analysis of selected GPCR-_fAAB positive samples. A: positive chronotropic GPCR-_fABBs: α₁-_fAAB, β₂-_fAAB and NOC-_fAAB and B: negative chronotropic GPCR-_fABBs: ETA-1-_fAAB, MAS-_fAAB samples were preincubated with 0.2 ​μg of the corresponding competing loop peptides as indicated under Material and methods for 30 ​min before the mixture was added to the cells for the recording of the corresponding GPCR-_fAAB effect. In the case of competition, the chronotropic response was abolished, which was achieved in four cases by the loop peptides specific to the 2nd extracellular loops. Only the α₁-_fAAB targeted the 1^st extracellular loop.