Functionally active autoantibodies targeting G-protein-coupled receptors in patients with Long-COVID
Autoimmunity is a factor in the pathogenesis of neurodegenerative disorders (e.g. glaucoma). Our recent data showed that functional active (i.e. agonistic) autoantibodies targeting the ß2-adrenergic receptor (ß2-AAb) are present in sera and aqueous humor of patients with glaucoma, contrary not in controls. ß2-receptors (ß2-AR) are present on cells of the trabecular meshwork (TM) and the ciliary body (CB), both involved in the regulation of the main risk factor (intraocular pressure, IOP). A steady-state of production of the aqueous humor (CB) and its main outflow pathway (TM) determine the IOP. Binding of ß2-AAb to ß2-AR can lead to an overstimulation and loss of desensibilisation of the receptor, contrary to ß2-blocker, commonly used as antiglaucomatous therapy. Thus, stimulation of ß2-AAb results in a chronic stimulation of the ß2-AR. A clinical proof-of-principal study showed that IOP decreased and/or number of local antiglaucomatous eye drops decreased after an unspecific extracorporal immunoadsorption, which eliminated ß2-AAb. A third target of ß2-AAb might be seen in the microcirculation. ß2-AAb correlate with retinal vascular characteristics in patients with glaucoma, measured by non-invasive OCT-angiography (OCT-A) and Heidelberg Retina Flow Meter. This observation might argue for a link between an increased IOP and vascular dysregulation, both mediated by ß2-AAb, respectively.
This pathophysiological hypothesis was transferred interdisciplinary to Long-COVID (LC). SARS-CoV-2 triggers the immune and autoimmune system already during acute infection (COVID-19). Stimulation of autonomic receptors (e.g. adrenergic) can disturb cellular homeostasis. If this autonomic dysbalance passes a threshold, clinical symptoms can occur. The idea of an „imbalanced autonomic theory“ was already published for the β-receptor in asthma in 1968. It is known that pathogens (e.g. infections, cancer) can induce the generation of AAb. Especially, functional AAb targeting G-protein-coupled receptors (GPCR-AAb) are of interest, as GPCRs mediate diverse functions in the human body. Further on, GPCRs are found on blood and endothelial cells, thus, we assume a GPCR-AAb induced impairment of capillary microcirculation. Our recent research data showed that sera of patients after COVID-19 yielded a high seropositivity of GPCR-AAb. Microcirculation was observed to be impaired in patients after COVID-19, mapped in the retina by OCT-A. Blood rheology was altered after COVID-19. Based on these data, we did a successful healing attempt in a patient with glaucoma and LC with the aim to neutralize the GPCR-AAb (by BC 007, BerlinCures GmbH), consequently increasing the impaired microcirculation and improving the patient’s symptoms.
The basis of each therapeutic attempt aiming to neutralize GPCR-AAb is a method for detection of these specific agonistic AAbs. Up to date the only test system is a cardiomyocyte bioassay, which is available at BerlinCures GmbH (Berlin, Germany). Yet, this method has restricted access for academic clinical and research approaches, thus it is the aim of the first clinician scientist to establish an alternative method for detection of functional active GPCR-AAb, namely the ß2-AAb. Therefore, we plan to establish a reporter-cell-based and exosome-based assay for reproducible detection of activating and binding ß2-AAb, respectively. These methods will be validated with data of the cardiomyocyte bioassay, being established in cooperation with Dr. Kräter (Max-Plank-Institut for the Science of Light) and Dr. Wallukat (BerlinCures GmbH). A promoter-controlled regulation of the receptor expression might offer an additional option to establish an adjustable cell-based system. After establishment of this bioassay we plan to screen sera of patients with Long-COVID with the perspective to derive monoclonal antibodies with stimulatory capacity for ß2-AR. As the cardiomyocyte bioassay is limited in capacity, the establishment of a novel diagnostic method for detection of GPCR-AAb would offer an independent alternative for academics to screen in a fast and efficient way different disease entities with an involvement of GPCR-AAb. Subsequent clinician scientists will use the established assays to derive monoclonal antibodies from Long-COVID patients for functional analyses.
