Complexity of synovial fluid-derived monocyte–macrophage lineage cells in knee osteoarthritis

Synovial fluid (SF)-derived monocyte–macrophage lineage (MON–Mϕ) cells in knee osteoarthritis (KOA) remain poorly understood. This lineage consists of four subpopulations with considerable interindividual variability that correlates with the distribution and activation of other immune cells. The most abundant subpopulation was that of CD11b+CD14−CD16− myeloid dendritic cells (mDCs; type cDC2), which were inactive and exhibited low cytokine production, low T-lymphocyte stimulation, high migratory ability comparing to other MON–Mϕ cells. Other major subpopulations included CD11b+CD14+CD16− monocyte-like cells and CD11b+CD14+CD16+ macrophages. A subpopulation of CD11b−CD14−CD16− mDCs (type cDC1) was less common. To confirm the identity of MON–Mϕ subpopulations characterised through flow cytometry, we performed bulk RNA-seq analysis on sorted CD11b+CD14−CD16−, CD11b+CD14+CD16− and CD11b+CD14+CD16+ MON–Mϕ subpopulations from the SF of four patients with KOA with a predominance of MON–Mϕ lineage cells. The CD11b+CD14+CD16− and CD11b+CD14+CD16+ cells shared a similar transcriptomic profile. However, CD11b+CD14−CD16− cells were remarkably distinct from other CD11b+ populations. The dataset is part of a study published by Mikulkova et al. Cell Reports.