Multiple sclerosis risk variants alter expression of co-stimulatory genes in B cells.

Ide Smets,Wenjia Liao,An Goris,Stephanie Humblet-Baron,Joanne Jones,Stephen Sawcer,Barnaby Fiddes,Alasdair Coles,James Dooley,George Wang,Josselyn E Garcia-Perez,Adrian Liston,Bénédicte Dubois,Maria Ban,Alastair Compston,Klara Mallants,Di He

doi:10.1093/brain/awx372

Abstract

The increasing evidence supporting a role for B cells in the pathogenesis of multiple sclerosis prompted us to investigate the influence of known susceptibility variants on the surface expression of co-stimulatory molecules in these cells. Using flow cytometry we measured surface expression of CD40 and CD86 in B cells from 68 patients and 162 healthy controls that were genotyped for the multiple sclerosis associated single nucleotide polymorphisms (SNPs) rs4810485, which maps within the CD40 gene, and rs9282641, which maps within the CD86 gene. We found that carrying the risk allele rs4810485*T lowered the cell-surface expression of CD40 in all tested B cell subtypes (in total B cells P ≤ 5.10 × 10-5 in patients and ≤4.09 × 10-6 in controls), while carrying the risk allele rs9282641*G increased the expression of CD86, with this effect primarily seen in the naïve B cell subset (P = 0.048 in patients and 5.38 × 10-5 in controls). In concordance with these results, analysis of RNA expression demonstrated that the risk allele rs4810485*T resulted in lower total CD40 expression (P = 0.057) but with an increased proportion of alternative splice-forms leading to decoy receptors (P = 4.00 × 10-7). Finally, we also observed that the risk allele rs4810485*T was associated with decreased levels of interleukin-10 (P = 0.020), which is considered to have an immunoregulatory function downstream of CD40. Given the importance of these co-stimulatory molecules in determining the immune reaction that appears in response to antigen our data suggest that B cells might have an important antigen presentation and immunoregulatory role in the pathogenesis of multiple sclerosis.

Highlights

Multiple sclerosis is an autoimmune disease of the central nervous system that is characterized pathologically by inflammation, demyelination and axonal loss
In order to study the effect of multiple sclerosis risk variants mapping within the genes for CD40 and CD86 on the surface expression of these co-stimulatory molecules in B cells we collected peripheral blood mononuclear cells (PBMCs) from 68 untreated multiple sclerosis patients and 162 healthy volunteers (Supplementary Table 1)
By applying detailed immunophenotyping in untreated multiple sclerosis patients and healthy controls, we have demonstrated that cell surface expression of the co-stimulatory molecules CD40 and CD86 on B cells is influenced by local genetic variants associated with disease susceptibility, suggesting that B cells contribute to the pathogenesis of the disease

Summary

Introduction

Multiple sclerosis is an autoimmune disease of the central nervous system that is characterized pathologically by inflammation, demyelination and axonal loss. The associated regions are heavily enriched for genes with known immunological function, pointing to a primary role of the adaptive immune system in the pathogenesis of the disease (The International Multiple Sclerosis Genetics Consortium and The Wellcome Trust Case Control Consortium 2, 2011; The International Multiple Sclerosis Genetics Consortium, 2013; Dendrou et al, 2015) Because of their limited contribution to the induction of experimental autoimmune encephalomyelitis (EAE) in mouse models, the contribution of B cells to multiple sclerosis development has long been overshadowed by investigation into T cells. In this study we assessed surface expression of key co-stimulatory molecules (CD40 and CD86) on B cell subtypes in patients with untreated multiple sclerosis and healthy control subjects, and correlated our findings with genotype at associated SNPs rs4810485 and rs9282641

Methods

Results

Conclusion