W123 - Increased CD56 Expression in Rheumatoid Arthritis Is Driven by ‘Double Positive’ CD56hiCD16hi NK Cells

Abstract Text: CD56+ natural killer (NK) cell subsets can contribute to inflammation through inflammatory cytokines and cytotoxicity, and in inflammatory conditions such as rheumatoid arthritis (RA), ‘double positive’ CD56hiCD16hi NK cells have been reported. Because CD56 and CD16 are not exclusive to NK cells, others interpret these cells as CD56+ monocytes or dendritic cells. We thus aimed to comprehensively characterize CD56+ and CD16+ immune cells in RA. Using flow cytometry, we studied blood from RA patients and matched healthy donors (n = 16 each). We screened for CD56+ subpopulations (CD3–CD19–) by applying the SPADE (Spanning-tree Progression Analysis of Density-normalized Events) algorithm on an index patient (severe polyarticular RA). We quantified the resulting populations using conventional bi-axial gating, measuring mean fluorescence intensities (MFI) of cell surface molecules. We used SPADE on CD16+ subpopulations to further distinguish CD56+CD16+ NK from other CD16+ cells. RA patient blood contained a distinct ‘double positive’ CD56hiCD16hi subpopulation which was significantly expanded compared to healthy donors (p < 0.001). Unsupervised SPADE clustering showed additional populations significantly increased in RA, including CD56+CD16+ low-density neutrophils (p = 0.003) and dendritic cells (p = 0.027). In the index patient, CD16 increases were seen in CD11c+ dendritic cells and CD15+ monocytes. CD56+ cells are shifted towards CD56hiCD16hi ‘double positive’ NK cells, whereas the more modest CD56 and CD16 increases in dendritic cells suggest they are secondary to the inflammatory interferons and cytokines characteristic in RA.