P135 Association of Serum Anti-Muscarinic 3 Antibodies with Gastrointestinal Disease in Systemic Sclerosis
Authors: Roblin Elen , Beesley Claire , Maclean Rory , Ahmed Fiza , Murray Charles , Ong Voon H , Denton Christopher 
Published: April 2024

Abstract

Background/Aims
Gastrointestinal (GI) complications of systemic sclerosis (SSc) are frequent and debilitating with symptoms ranging from reflux to faecal soilage. The pathogenesis of GI disease in SSc is poorly understood. Circulating antibodies against Muscarinic type 3 Receptors (anti-M3R) have been implicated in GI smooth muscle dysfunction and neural activation impairment. We examine whether anti-M3R antibodies associate with objective measures of gastrointestinal symptoms.

Methods
Sera were collected from SSc patients fulfilling the American College of Rheumatology (ACR) classification criteria for SSc. Healthy control (HC) sera were obtained from age-matched volunteers. SSc patients completed the UCLA GIT 2.0 (UCLA GIT) questionnaire. Serum anti-M3R antibodies were measured using specific enzyme-linked immunosorbent assay (ELISA)(CellTrend GmbH, Germany). SSc sera had elevated anti-M3R antibodies if the concentration exceeded two standard deviations above the mean of HC sera. Statistical comparisons were made using Fisher’s exact test and two sample t-test.

Results
Sera from 40 SSc patients and five HC were assayed for anti-M3R antibodies. Anti-M3R antibody was higher in SSc patients in comparison to HC (1547 vs 1183U/ml, p = 0.33). Anti-M3R antibody levels were significantly elevated in nine (23%) SSc patients. Cohort characteristics were compared based on anti-M3R antibody levels for SSc patients (Table 1). Group demographics were similar in gender, age and disease duration. There was a trend for higher anti-M3R antibodies in limited compared with diffuse cutaneous SSc subset (66.7 vs 32.2, p = 0.12). Although there was no significant association between Anti-M3R antibody level and GIT score (r = 0.014 p = 0.51), SSc patients with elevated anti-M3R antibody did report numerically more severe reflux symptoms (1.24 vs 0.8, p = 0.23) and fewer lower GI domains of severe soilage (0.56 vs 0.87, p = 0.37) and constipation (0.28 vs 0.52, p = 0.2).

Conclusion
These results show that there is a subset of SSc patients with elevated anti-M3R antibodies which could be pathogenic by perturbing cholinergic neurotransmission in the GI tract. The trend observed of elevated anti-M3R antibodies with more severe GI symptoms warrants further exploration in a larger cohort of SSc. If confirmed, our findings provide mechanistic rationale for reported benefit from intravenous immunoglobulin on symptom severity in SSc GI disease.

Disclosure
E. Roblin: None. C. Beesley: None. R. Maclean: None. F. Ahmed: None. C. Murray: None. V.H. Ong: None. C. Denton: Consultancies; C.P.D. has received consulting fees from Arxx Therapeutics, Roche, Janssen, GlaxoSmithKline, Bayer, Sanofi, Galapagos, Boehringer Ingelheim, CSL Behring and Acceleron. Honoraria; C.P.D. has received honoraria from Janssen, Boehringer Ingelheim, and Corbus. Grants/research support; C.P.D. has received research grants to the institution from Servier, Horizon, Arxx Therapeutics and GlaxoSmithKline.