Functionally impaired plasmacytoid dendritic cells and non-haematopoietic sources of type I interferon characterize human autoimmunity

Autoimmune connective tissue diseases arise in a stepwise fashion from asymptomatic preclinical autoimmunity. Type I interferons have a crucial role in the progression to established autoimmune diseases. The cellular source and regulation in disease initiation of these cytokines is not clear, but plasmacytoid dendritic cells have been thought to contribute to excessive type I interferon production. Here, we show that in preclinical autoimmunity and established systemic lupus erythematosus, plasmacytoid dendritic cells are not effector cells, have lost capacity for Toll-like-receptor-mediated cytokine production and do not induce T cell activation, independent of disease activity and the blood interferon signature. In addition, plasmacytoid dendritic cells have a transcriptional signature indicative of cellular stress and senescence accompanied by increased telomere erosion. In preclinical autoimmunity, we show a marked enrichment of an interferon signature in the skin without infiltrating immune cells, but with interferon-κ production by keratinocytes. In conclusion, non-hematopoietic cellular sources, rather than plasmacytoid dendritic cells, are responsible for interferon production prior to clinical autoimmunity

Diversification of human plasmacytoid predendritic cells in response to a single stimulus

Innate immune cells adjust to microbial and inflammatory stimuli through a process termed environmental plasticity, which links a given individual stimulus to a unique activated state. Here, we report that activation of human plasmacytoid predendritic cells (pDCs) with a single microbial or cytokine stimulus triggers cell diversification into three stable subpopulations (P1-P3). P1-pDCs (PD-L1(+)CD80(-)) displayed a plasmacytoid morphology and specialization for type I interferon production. P3-pDCs (PD-L1-CD80(+)) adopted a dendritic morphology and adaptive immune functions. P2-pDCs (PD-L1(+)CD80(+)) displayed both innate and adaptive functions. Each subpopulation expressed a specific coding-and long-noncoding-RNA signature and was stable after secondary stimulation. P1-pDCs were detected in samples from patients with lupus or psoriasis. pDC diversification was independent of cell divisions or preexisting heterogeneity within steady-state pDCs but was controlled by a TNF autocrine and/or paracrine communication loop. Our findings reveal a novel mechanism for diversity and division of labor in innate immune cells

The activation trajectory of plasmacytoid dendritic cells in vivo during a viral infection

International audiencePlasmacytoid dendritic cells (pDCs) are a major source of type I interferon (IFN-I). What other functions pDCs exert in vivo during viral infections is controversial, and more studies are needed to understand their orchestration. In the present study, we characterize in depth and link pDC activation states in animals infected by mouse cytomegalovirus by combining Ifnb1 reporter mice with flow cytometry, single-cell RNA sequencing, confocal microscopy and a cognate CD4 T cell activation assay. We show that IFN-I production and T cell activation were performed by the same pDC, but these occurred sequentially in time and in different micro-anatomical locations. In addition, we show that pDC commitment to IFN-I production was marked early on by their downregulation of leukemia inhibitory factor receptor and was promoted by cell-intrinsic tumor necrosis factor signaling. We propose a new model for how individual pDCs are endowed to exert different functions in vivo during a viral infection, in a manner tightly orchestrated in time and space