Circulating b cell subsets and cytokine gene expression levels in peripheral blood and skin biopsy in chronic inflammatory demyelinating polyneuropathy

Presentation of the Thesis: Ozdag Acarli A.N., Circulating B Cell Subsets and Cytokine Gene Expression Levels in Peripheral Blood and Skin Biopsy in Chronic Inflammatory Demyelinating Polyneuropathy. Department of Neurology, Istanbul Faculty of Medicine, Istanbul University, Thesis in Neurology, Istanbul, 2019. Objective: Chronic inflammatory demyelinating polyneuropathy (CIDP) is the most common treatable chronic immune mediated neuropathy worldwide and the efficacy of intraveneous immunglobulin (IVIg) and plasma exchange in the treatment of CIDP suggests a pathogenetic contribution of humoral factors. This study aimed to analyse peripheral B-cell homeostasis, B-cell mediated IL6, IL10 and TNFA mRNA expression levels in peripheral mononuclear blood cells and skin biopsy specimens, intraepidermal nerve fiber densities (IENFD) in CIDP patients compared to healthy and disease control groups. We also investigated their value as a biomarker, our results suggest that they can be an useful tool to detect disease activity status and treatment effect in CIDP drug trials. Patients and Methods: The study included 50 CIDP (25 typical CIDP, 18 MADSAM, 7 DADS-I) patients. Twenty-five age-matched healthy donors (HC) and 13 patients with CMT1A served as disease controls. Peripheral B-cell homeostasis of all patients were analysed by multi-color flow cytometry. B-cell mediated IL6, IL10 and TNFA mRNA expression levels in peripheral mononuclear blood cells (PBMC) and in skin biopsy specimens were also evaluated by real-time polymerase chain reaction. Seventeen CIDP cases and 10 HCs underwent 3 mm skin biopsies at different levels in the forearm, thigh and distal leg. Sections were stained with anti-PGP9.5. Intraepidermal nerve fiber densities (IENFD) were measured. Correlations between B cell populations, cytokine gene expression levels, IENFD and functional disability were evaluated. Results: We detected significant reduction in total B cells (p=0.0002), naive B cells (p=0.0012) and plasma cells (p<0.0001) and an elevation in switched memory B cells (p=0.0004) in CIDP patients compared to control groups. Plasma cell percentages were reduced in the typical CIDP group compared to atypical CIDP (p=0.0191). On the other hand, typical CIDP and atypical CIDP subjects both had reduced plasma cell percentages compared to control groups and no differences were found in other B cell subtypes in groups of typical and atypical CIDP. CIDP cases had significantly higher TNFA gene expression levels in PBMC compaired to HC (p=0.0191). There were no significant difference in IL6 and IL10 gene expression levels in PBMC between gropus of CIDP and HC. IL6 and TNFA gene expression levels in skin biopsies were not different in CIDP subgroups and HC. IENFD was significantly reduced in all three skin biopsy regions in CIDP patients vs. healthy controls (respectively for distal leg, thigh and forearm; p<0.0001, p=0.003 ve p=0.002). Lower nerve fiber densities correlated with functional disability (cc=-0,563, p=0,019) and the duration from last CIDP attack to skin biopsy (cc=0,494, p=0.044). Discussion: Decreased total B, naive B and plasma cells, and elevated numbers of switched memory B cells in peripheral blood and TNFA gene expression levels in PBMC in CIDP indicate an overactivity in humoral immune system, and represent a typical signature in both typical and atypical CIDP as indicated above. Investigating the underlying mechanisms of changes in the B cell population will guide the development of novel treatment modalities in CIDP. Skin is an attractive tissue to establish disease activity status and has great potential as a biomarker to detect treatment response and follow-up in CIDP. Key Words: Chronic inflammatory demyelinating polyneuropathy, B cells, cytokine, intraepidermal nerve fibers, skin biopsy