Background Dendritic cell (DC) are a heterogeneous group of antigen presenting cells that can be subdivided into CD1c and CD141+DC. CD141+DC were first discovered in 2010 and little is known about their function in health or disease. No previous studies on CD141+DC in inflammatory arthritis (IA) have been performed therefore our aim was to examine if these newly described DC play a pathogenic role in IA.
Methods CD141+DC were purified from SFMC/PBMC, stimulated and stained with a panel of DC specific activation markers. CD141+DC were cocultured with T cells for 6d basally or in the presence of TREM-1 after which intracellular cytokine production was assessed by flow cytometry. Supernatants from DC-T cell cocultures were used to treat synovial fibroblasts and the expression of adhesion molecules, cytokines and MMPs was measured. CD141+DC were also identified in synovial-tissue by immunohistology/flow cytometry for CD141/CLEC9A/TREM-1. Finally using sorted populations of CD141+DC from SFMC and PBMC, RNA sequencing was performed and differentially expressed genes and interaction network analysis were identified using the DeSeq2 R package, Ingenuity® Pathway Analysis (IPA) and InnateDB and Cytoscape.
Results SF-CD141+DC are significantly enriched compared to WB and express higher levels of activation markers CD80/CD86 and CD40. SF-CD141+DC induced both CD8+ and CD4+T cell proliferation, granzyme B production from CD8+ and TNFα, IFNγ and GMCSF from CD4+T cells. Supernatants from CD141+DC activated T cells subsequently induced synovial fibroblast expression of ICAM-1, IL-6, IL-8, MMP1 and MMP3. SF-CD141+DC expressed significantly higher levels of the the hypoxia marker TREM-1, activation of which further induces expression of CD80, CD86 and CD40. Coculture of these TREM-1 activated CD141+DC with CD3+ T cells increased IFNγ and IL-17a production. Finally RNASeq analysis revealed that there are 2089 differentially expressed genes between SF-CD141+DC and PBMC CD141+DC, with induction of a number of key network pathways identified in SF CD141+ DC, including energy metabolism, chemokine and cytokine signalling.
Conclusion CD141+ DC are enriched in the IA joint in an active state. RNASeq analysis revealed they are distinct from blood CD141+DC and our in vitro data would support the hypothesis that these CD141+DC contribute to synovial inflammation and joint destruction.