Antibodies to the Muscarinic Acetylcholine Receptor M3 in Primary Biliary Cholangitis Inhibit Receptor Function on Cholangiocytes

Abstract

Background and Aims: In primary biliary cholangitis (PBC), antibodies to a peptide of the muscarinic acetylcholine receptor 3 (mAChR3) have been described. Since the mAChR3 is expressed on cholangiocytes and mAChR3-signaling is involved in the pathogenesis of chronic inflammatory biliary diseases, we wanted to investigate whether anti-mAChR3-antibodies influence the function of the receptor and the proliferative response of cholangiocytes. Methods: Immunoglobulins were isolated by ammonium sulfate precipitation using sera from patients with PBC ( n = 63) and with other chronic liver disorders ( n = 150). All immunoglobulins were analyzed by a luminometric assay using Chinese hamster ovary (CHO) cells overexpressing the mAChR3 and cholangiocytes (TFK-1-cells) expressing the receptor constitutively. Cell proliferation was measured by 3 H-thymidine assay. PBC patients were also analyzed in the follow-up. Results: Antibodies inhibiting the mAChR3 were found in 49 and 79% of PBC patients using CHO-cells or TFK-1-cells, respectively, but only in up to 26% of controls ( p < 0.01). Stimulatory antibodies were hardly detected. Antibody reactivity only marginally changed during the course of the disease, independently of the choice of treatment (ursodeoxycholic acid, immunosuppressive therapy, or no medication). There was no correlation with laboratory, clinical or histological parameters, but the antibodies were more frequently found in PBC patients with a benign course (96%) than in patients with active disease progressing to late stages within 10 years (57%; p < 0.01). Proliferation of cells was not influenced by immunoglobulins from PBC-patients. Conclusion: Sera from patients with PBC contain inhibitory antibodies to the mAChR3 on cholangiocytes (TFK-1 cells) without influencing TFK-1-cell proliferation. These antibodies were predominantly observed in patients with non-progressing PBC.

Functionally Active Antibodies to the Angiotensin II Type 1-Receptor Measured by a Luminometric Bioassay Do Not Correlate With Clinical Manifestations in Systemic Sclerosis: A Comparison With Antibodies to Vascular Receptors and Topoisomerase I Detected by ELISA

“…We, therefore, wanted to see whether functionally active anti-AT 1 R may occur also in another disease complex and selected patients with chronic liver disorders in which we had observed another functional antibody directed against the muscarinic receptor type 3 in a previous study ( 11 , 34 ). Indeed, up to 50% of patients with autoimmune liver disorders and even up to 70% of patients with toxic or viral hepatitis had stimulatory or inhibitory anti-AT 1 R antibodies.…”

Potential Role for Combined Subtype-Selective Targeting of M1 and M3 Muscarinic Receptors in Gastrointestinal and Liver Diseases

“…PBC is more commonly associated with anti-M 3 R antibodies than other liver diseases ( Tsuboi et al, 2014 ); those with anti-M 3 R antibodies are more likely to have a benign disease course. Nonetheless, M 3 R antibody levels do not correlate with treatment responses or serological markers either at baseline or during the disease course ( Mayer et al, 2020 ). A subset of patients with PBC develop Sjogren’s syndrome; the shared increase in anti-M 3 R antibody levels in both conditions suggests overlapping features could form the basis for a mutual treatment.…”

Evaluation of Inhibitory Antibodies against the Muscarinic Acetylcholine Receptor Type 3 in Patients with Primary Biliary Cholangitis and Primary Sclerosing Cholangitis

“…We were able to show a potential inhibitory function of these mAChR3 auto-ab in vitro [26] and, moreover, we have recently shown that isolated mAChR3inh+ auto-ab inhibit mAChR3 function in BECs in vitro [27].…”