Background/Purpose: Dendritic cells (DCs) are a heterogeneous population of professional antigen-presenting cells which are at the interface between innate and adaptive immunity. There are different DCs subsets, classified according to their tissue location and their functions. 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 a specific subset of DC CD209⁺/CD14⁺ and evaluate their characteristics in the periphery of patients with inflammatory arthritic (IA). In addition, it aimed to evaluate the enrichment and activation of these cells at the site of inflammation, the join 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 subject (HC), RA and PsA patients. Single cell synovial tissue suspension from RA and PsA patients was obtained by enzymatic digestion. PBMC, SFMC and synovial tissue cell suspensions were analysed by flow cytometry to identify the CD209⁺/CD14⁺ DC subset and its frequency. Expression of chemokines receptors (CCR6, CCR7, CXCR3, CXCR4 and CXCR5) and activation markers (CD40 and CD80) on the surface of the CD209⁺/CD14⁺ DC subset were also evaluated by flow cytometry.

Results: We identified, for the first time, the CD209⁺/CD14⁺ DC population in PBMC of RA and PsA patients and HC, with no significant differences among the groups. Interestingly, we observed that this population was enriched in SFMC of RA and PsA patients, with a further increased frequency demonstrated in the synovial tissue cell suspensions. This was paralleled by a more mature phenotype of the DC subset at the site inflammation compared to periphery, with a significant increase in CD40 (p< 0.01) in PsA patients and CD40 and CD80 in RA patient (p< 0.01).  In addition, SPICE analysis identified a differential expression and co-expression of chemokine receptors at the periphery of RA and PsA patients, when compared to the HC, suggests that DCs in the periphery are already activated to migratory to sites of inflammation in IA. We further observed a unique profile of chemokines receptors in single cell analysis of synovial tissue cell suspension demonstrating increased expression of both and CXCR3 (p< 0.01) and CXCR5 (p< 0.001) in RA and PsA.

Conclusion: We identify for the first time a monocyte-derived DC population characterised as CD209⁺/CD14⁺ in the periphery of RA and PsA patients. This population was enriched at the site of inflammation and displayed a unique chemokine receptor profile and activation markers, suggesting these cells are already activated in the periphery of IA patients, and are recruited and further activated into the joint of IA patients.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/cd209-cd14-dendritic-cells-characterization-in-rheumatoid-versus-psoriasis-arthritis-patients/