Background/Purpose: Synovial tissue macrophages are an exquisitely plastic pool of innate cells that play a key role in RA disease progression. However, the precise nature, diversity and function of macrophage subsets within the inflamed joint remains unexplored.

Methods: Single cell analysis of Rheumatoid Arthritis, Psoriatic Arthritis, Osteoarthritis and healthy control synovial tissue biopsies and synovial fluid mononuclear cells was performed using advanced flow cytometry with the following panel (CD40, CD45, CD64, CD68, CD163, CD206, CD253, CCR4, CCR7, CXCR1, CXCR3). CD206+CD163+ and CD206-CD163- macrophages were sorted from RA synovial tissue by FACSAria sorter for subsequent RNAseq, FLIM analysis and autologous T-cell co-culture experiments.

Results: RA synovial tissue and fluid macrophages display markers typical of both M1 (CD40+CD253+) and M2 (CD206+CD163+) macrophages with a spectrum of macrophage activation states identified in RA synovial tissue that don’t fully conform to the classic M1/M2 framework. Within this spectrum, significant enrichment of a dominant CD206+CD163+ macrophage-subtype is present in synovial tissue versus fluid (p< 0.05). CD206+CD163+ synovial tissue macrophages express significantly more CD40 compared to synovial fluid (p< 0.0003), positively correlate with disease activity (r=0.6, p< 0.01), with baseline levels predicting response to therapy (p< 0.05). Moreover, CD206+CD163+CD40+ macrophages are enriched in RA synovial tissue compared to PsA and OA pathotypes (p< 0.05) and display distinct chemokine receptor expression patterns. While the CD206+CD163+ macrophage subset is present in healthy synovial tissue, expression of CD40 is completely absent in the healthy synovium (p< 0.05). RNA-seq analysis indicates that the CD206+CD163+ population is transcriptionally distinct from synovial tissue CD206-CD163-, synovial fluid CD206+CD163+, and pure RA monocyte-derived M1/M2 macrophages, with unique tissue-resident gene signatures (TREM2+, FOLR2+, LYVE1+ C1QA+, TIMD4+, CD48-, CCR2-). Moreover, differing metabolic demands between CD206+CD163+ and CD206-CD163- subsets was demonstrated by RNAseq and FLIM analysis. Finally, CD206+CD163+ macrophages have the capacity to induce autologous T-cell responses and spontaneously secrete high levels of pro-inflammatory cytokines, thus further contributing to the local inflammatory response.

Conclusion: This data identifies enrichment of a previously undescribed dysfunctional dominant and transcriptionally distinct macrophage subtype in RA synovial-tissue.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/significant-enrichment-of-transcriptionally-distinct-cd206cd163-macrophage-population-in-rheumatoid-arthritis-synovial-tissue/