FRI0263 Characterisation of epithelium-associated fcrl4+ b cells from parotid glands of patients with sjÖgren’s syndrome using single cell rna sequencing
Authors: G.M. Verstappen, J.A. Ice, H. Bootsma, S.A. Pringle, E.A. Haacke, F.K. Spijkervet, C.J. Lessard, F.G. Kroese
Journal: Annals of the Rheumatic Diseases (2018)

<h3>Background</h3> A subset of B cells expressing the inhibitory Fc receptor-like protein 4 (FcRL4) is found in salivary gland lesions of patients with primary Sjögren's syndrome (pSS). FcRL4 +B cells are associated with ductal epithelial cells forming lymphoepithelial lesions (LEL), in particular within parotid glands<sup>1</sup>. Furthermore, FcRL4 is expressed by mucosa-associated lymphoid tissue (MALT) lymphoma B cells. <h3>Objectives</h3> We aimed to investigate, by single cell and bulk RNA sequencing, how the gene expression profile of FcRL4 +B cells differs from FcRL4-negative naive and memory B cells in salivary gland tissue from pSS patients. We hypothesised that FcRL4 +B cells contribute to LEL formation and are prone to lymphomagenesis. <h3>Methods</h3> Parotid gland biopsies of 5 pSS patients without MALT lymphoma were obtained. Single cell suspensions were prepared by mechanical disruption and enzymatic digestion. The cells were incubated with anti-CD19, anti-CD27 and anti-FcRL4 antibodies, and sorted as single cells or 5 cells per well based on the following definitions: CD19 +CD27-FcRL4- ('naive'), CD19 +CD27+FcRL4- (memory) and CD19 +FcRL4+ (FcRL4+). Library preparation was done using an in-house SMARTseq2 protocol and sequencing was done on an Illumina HiSeq2500. <h3>Results</h3> Samples from 4 pSS patients passed quality control and were included. A total of 160 single cells and 360 cells in bulk were included in the analysis. Genes identified by differential expression were subjected to gene pathway analysis. Both in single cell and bulk samples, multiple genes coding for integrins, such as <i>ITGAX</i> (CD11c), were significantly upregulated in FcRL4 +B cells. Gene Ontology pathways that showed the highest upregulation in FcRL4 +B cells (both single cell and bulk) were receptor binding, GTPase and protein kinase pathways. Analysis of bulk samples further revealed that expression levels of genes encoding for Src tyrosine kinases, genes involved in the NF-κB pathway, <i>CXCR3</i>, and<i> TNFRSF13B</i> (TACI)<i>,</i> among others, were significantly upregulated in FcRL4 +B cells, compared with either naive or memory B cells. Expression levels of <i>CD40</i> were significantly decreased in FcRL4 +B cells. <h3>Conclusions</h3> FcRL4 +B cells in salivary glands of pSS patients show upregulation of genes involved in homing and cell adhesion, consistent with their tissue location close to the epithelium. FcRL4 +B cells also show increased levels of transcripts that induce inflammation and B cell survival. These cells exhibit all characteristics of chronically stimulated CD11c+memory B cells, and we speculate that FcRL4 +B cells contribute significantly to the epithelial damage seen in the glandular tissue of pSS patients. <h3>Reference</h3> [1] Haacke, et al. J Autoimmun. 2017;81:90–8. <h3>Acknowledgements</h3> We thank Kim de Lange and Gerben van der Vries from the Genome Analysis Facility of the University Medical Centre Groningen for excellent technical and bioinformatics assistance. <h3>Disclosure of Interest</h3> None declared