19A166

Divergent Roles of Rheumatoid Arthritis Synovial Dendritic Cells

Author(s)

Mary Canavan 1, Viviana Marzalioli 1, Vipul Bhargava 2, Ronan Mullan 3, Douglas J Veale 4, Ursula Fearon 1

Department(s)/Institutions

1 Molecular Rheumatology, Trinity Biomedical Sciences Institute, Trinity College Dublin. 2 Janssen Research & Development, Spring House, Pennsylvania, USA 3 Department of Rheumatology, Adelaide and Meath Hospital, Dublin 4 Centre for Arthritis and Rheumatic Diseases, St Vincents University Hospital, Dublin

Introduction

Dendritic Cells (DC) are potent antigen presenting cells which can be subdivided into CD141
and CD1c DC. We reported a previously unacknowledged role of CD141 + DC in the RA
synovium however, the identification and function of CD1c + in RA has yet to be fully
elucidated.

Aims/Background

To investigate if CD1c + DC are present in the RA synovium and if they are transcriptionally and functionally distinct to synovial CD141 + DC.

Method

Synovial biopsies were obtained via arthroscopy and enzymatically and
mechanically dissociated to yield a single cell suspension. Synovial fluid mononuclear cells
(SFMC) and peripheral blood mononuclear cells (PBMC) in addition to synovial tissue digests
were stained with a panel of fluorochrome conjugated antibodies and analysed by
multicolour flow cytometry. CD1c + DC and CD141 + DC were magnetically sorted from RA
synovial fluid and cocultured with allogeneic CTV labelled T cells. Finally, RNA sequencing
was performed on sorted synovial CD1c and CD141 DC and downstream bioinformatic
analysis was performed.

Results

A distinct population of CD1c+ DC were identified in the RA synovium with high
expression of DC maturation markers CD80 and CD40. CD1c + DC express high levels of the
chemokine receptors CCR7 and CXCR4 suggestive of increased
migration of DC to the joint. Furthermore, upon examination of peripheral blood and
synovial fluid CD1c + DC, we demonstrate increased frequencies of CD1c + DC in the synovium
compared to peripheral blood. Synovial CD1c + DC are transcriptionally distinct from synovial
CD141 + DC as identified but Principal component analysis (PCA) and hierarchical clustering
analysis. Moreover, IPA analysis revealed that pathways involved in T cell activation, T cell
exhaustion and DC maturation were upregulated in synovial CD1c + DC compared to
CD141 + DC. Following coculture of allogeneic T cells with either synovial CD1c + DC or
CD141 + DC we noted a preferential induction of CD4 + T cell derived GMCSF, TNFα and IFNƴ in
CD1c + DC cocultures. However, CD141 + DC were superior in induction of a TNFα producing
CD8 + T cell population.

Conclusions

Mature CD1c DC are enriched in the RA joint and are transcriptionally distinct
from synovial CD141+DC. Synovial DC may play distinct roles in RA pathology via differential
T cell activation.