Single-cell RNA sequencing analysis unveils highly active yet diminished CD14+CD16-circulating monocytes, independent of alopecia areata severity

Introduction: Alopecia Areata (AA) is an autoimmune-driven hair loss condition with complex immunological underpinnings. Circulating monocytes are known for their active immune roles, yet their involvement in AA and the impact of disease severity remain unclear. with mild and severe AA, along with healthy controls. Methods: We conducted a comprehensive single-cell RNA sequencing (scRNAseq) analysis of peripheral blood mononuclear cells (PBMCs) from individuals with both mild and long-standing severe AA, in addition to healthy controls. Our approach involved cell clustering, differential expression, and functional analyses to unravel underlying insights. Results: The monocyte cluster exhibited gene expression patterns resembling various subtypes in AA patients, including 'S100A12', 'HLA-presenting', and 'pro-inflammatory' monocytes, indicating a complex response. Our analysis revealed significant depletion of highly active CD14+CD16- monocytes in mild and severe AA patients compared to healthy controls. CD14-CD16+ monocytes and cDC subsets displayed subtler transcriptomic changes. CD14+CD16- monocytes showed enriched immune pathways such as TLR signaling, interferon-gamma-mediated signaling, antigen presentation, supported by active RNA processing, translation, and metabolic processes (e.g., TYMP, CYBA, KYNU). Heightened activation for stress response (e.g., EIF1, FOS, JUNB) possibly linked to oxidative stress or protein misfolding (e.g., AHR, FKBP5, S100A8) was observed. Despite fewer CD14+CD16- monocytes, no transformation into CD14-CD16+ monocytes or cDC subtypes was observed. Conclusion: Our findings unveil a paradoxical scenario in AA, where diminished circulating CD14+CD16- monocyte counts coexist with heightened metabolic activity and diverse immune responses. This dual phenomenon persists regardless of disease severity, underscoring these monocytes pivotal role in systemic inflammation. This insight positions CD14+CD16- monocytes as potential central players in AA pathogenesis, highlighting their potential as therapeutic targets, even at the early diagnostic stage.