Background/Purpose: Dendritic cells (DCs) are a heterogeneous population of professional antigen-presenting cells which are at the interface between innate and adaptive immunity. A specific subset of DCs is known to derive from monocyte and has a key role in inflammation and infection.

This study aimed to identify and characterize the CD209⁺/CD14⁺ DC subset and evaluate their characteristics in the periphery of patients with inflammatory arthritic (IA) together with their enrichment and activation at the site of inflammation, the joint of rheumatoid (RA) and psoriatic arthritic (PsA) patients.

Methods: Peripheral blood and synovial fluid mononuclear cells (PBMC and SFMC) were isolated by Ficoll density gradient from healthy subjects (HC), RA and PsA patients. Single-cell synovial tissue suspension (ST) from RA and PsA patients was obtained by enzymatic digestion. PBMC, SFMC and ST were analysed by flow cytometry to identify the CD209⁺/CD14⁺ DC subset, its frequency and the expression of chemokines receptors (CCR6, CCR7/CXCR3/CXCR4/CXCR5) and activation markers (CD40 and CD80) on the surface of the DC subset. In addition, PBMC were stimulated with different TLR (LPS, CPG, Poly I:C) and intracellular staining for IL12/TNFα/IL1β/IL6 was performed. CD209⁺ DC were isolated with a two-step isolation protocol. Lineage negative cells (CD3/CD19/CD56^–) were stimulated with GMCSF/IL4 in the presence or absence of the JAK/STAT inhibitor Tofacitinib or the TNF inhibitor Humira and the CD209⁺/CD14⁺ DC was evaluated by flow cytometry.

Results: We identified, for the first time, the CD209⁺/CD14⁺ DC population in PBMC of RA and PsA patients, with similar frequency observed when compared to HC. However, we observed activation of circulating CD209/CD14⁺ DC from both RA and PsA patients, with higher production of cytokines (IL12/TNFα), in addition to expression/co-expression of chemokine receptors (CCR6/CCR7/CXCR3/CXCR4/CXCR5). Interestingly, we observed that this DC population was enriched at the site of inflammation, in SFMC and ST and displayed a mature phenotype, with a significant increase in CD40 and CD80 and co-expression of specific chemokine receptors, displaying unique patterns between PsA and RA. We developed a protocol of magnetic isolation for CD209⁺ DC from blood and observed that culturing HC CD209+DC with IA synovial fluid SF was sufficient to induce the development of CD209/CD14⁺ DC, leading to a poly-mature phenotype. Finally, we observed that JAK/STAT inhibition, but not TNF inhibitor, reduced the generation and development of CD209⁺/CD14⁺ DC.

Conclusion: We identified, for the first time, a monocyte-derived DC population characterized as CD209⁺/CD14⁺ DC in the periphery of RA and PsA patients. This population was enriched at the site of inflammation displaying a unique chemokine receptor profile and activation markers, suggesting cells, already activated in the periphery of IA patients, are then recruited activated further into the joint of IA patients. We observed that IA SF induce the development of CD209/CD14⁺ DC and their maturation. In addition, we demonstrated that the CD209⁺/CD14⁺ DC development is sensitive to JAK/STAT, but not TNF inhibition.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/cd209-cd14-dendritic-cells-characterization-in-rheumatoid-and-psoriatic-arthritis-patients-activation-synovial-infiltration-and-therapeutic-targeting/