Background & Aims
We have recently shown that either all, or a majority of patients with severe fibromyalgia syndrome (FMS) harbour immunoglobulin G autoantibodies which can explain FMS core phenotypic features. Upon injection to rodents, patients’ purified serum-IgG trigger pertinent disease features, meeting Witebsky-Rose criteria of direct proof for autoimmunity (1).
Increased binding to satellite glial cells was identified, but further cellular binding targets and downstream mechanisms of antibody binding have remained unknown. In historical studies increased densities of tissue resident mast cells were demonstrated in FMS skin, and a correlation between skin mast cell activation and protein extravasation (2,3).
We wished to clarify skin mast cell density in a cohort of UK patients with severe FMS.
Methods
Skin tissue sections were processed from patients with FMS (n=20) and controls (C) (n=16) on an automated immunohistochemistry platform and visualised using a 3,3′-Diaminobenzidine (DAB) detection kit. The study quantified anti-tryptase 1 (AA1) positive mast cells within 4µm paraffin-embedded tissue sections. Sections were imaged using an automated slide scanner. QuPath (Version 0.5.1) was used to identify mast cells positively stained with haematoxylin and AA1 using DAB in a standard research protocol for cell detection with a single gated threshold of 0.3 to categorise positive and negative cells. All statistical summaries and tests were conducted in Rstudio (Version 4.0.2). The total detections per mm2 (detections/area), total positive cells per mm2 (DAB positive/area) and cumulative positive percentage (total positive:total detections x 100) were calculated.
Results
There is a wide range in the data in the FMS group indicating variable mast cell density. Levene’s test of variances found a significant difference in variability (p=0.00018) indicative of within-FMS-group heterogeneity. There were increased mast cell densities in FMS relative to C (median [IQR]; FMS = 107.1 [66.7-138] cells/mm², C = 46.4 [43.5, 62.6] cells/mm²; p = 0.00060) and higher positive percentage in FMS compared to C (median [IQR]; FMS = 14.60% [9.1, 18.6], HV = 9.3% [7.5, 11.2]; p = 0.042). There were no differences in total cell detections.
Conclusions
We show that FMS skin mast cell density is increased vs HC by >100%, with strong variability between patients. We previously demonstrated that skin mast cells density in patients with severe CRPS is normal, suggesting that these FMS results are disorder-specific (4). We propose that the expansion and accumulation of dermal mast cells may be involved in autoimmune-mediated sensitisation of dermal nerve fibres in FMS. The degree of mast cell activity in the skin, the microenvironment of neuro-immune cell signalling and the role of mast cells in the generation and maintenance of pain in FMS warrants further study in both pre-clinical models and human skin. These results provide for a first time a rationale for the investigation of therapeutic pathways addressing the FMS autoimmune pathology downstream of FMS-IgG binding, i.e. beyond methods that reduce serum immunoglobulin.
The detected substantially abnormal FMS skin mast cell density, which sets FMS apart from other severe chronic pains may indicate abnormal release of pro-algetic mediators contributing to the FMS phenotype and might potentially explain effects downstream from binding of pro-algetic serum IgG. The strong and specific difference with HCs, in keeping with earlier studies, justifies citation of these findings by clinicians as supplementary evidence to better inform their patients about the FMS causes, who have been told that all their pain is centrally mediated or ‘in their head’. These findings open new avenues for the development of diagnostic tests and treatments.
References
(1) Goebel et al., JCI 2021
(2) Eneström et al., ScandJRheum 1997
(3) Blanco et al., ClinRheumat 2010
(4) Morellini et al., Pain, 2018
Presenting Author
Andreas Goebel
Poster Authors
Andreas Goebel MD, PhD
MD
University of Liverpool
Lead Author
Uazman Alam
Pain Research Institute, University of Liverpool
Lead Author
Anne Marshall
Pain Research Institute, University of Liverpool
Lead Author
Jamie Burgess
Pain Research Institute, University of Liverpool
Lead Author
Topics
- Specific Pain Conditions/Pain in Specific Populations: Fibromyalgia