Background/purpose Dendritic cells (DC) are key cells in the pathogenesis of autoimmune diseases by potently activating T-cells. Systemic lupus erythematosus (SLE) and antiphospholipid syndrome (APS) are characterised by an IFN signature, caused by elevated levels of IFNα. Plasmacytoid DC (pDC) are held responsible for the increased levels of IFNα in SLE and APS. The molecular mechanisms underlying the increased activation of pDC in SLE and APS are unknown. Using RNA sequencing (RNAseq) and further in vitro validation experiments on plasmacytoid and myeloid DC (mDC) obtained from patients with SLE and APS we assessed the causes and consequences of increased type I IFN signalling on the dysregulation of both pDC and mDC in patients with SLE and APS.
Methods RNAseq was performed on pDC and mDC isolated from peripheral blood of patients with SLE, SLE +APS and primary APS (PAPS) and healthy controls (n=54). Weighted gene correlation network analysis (WGCNA) was used to identify pDC- and mDC-specific gene modules and to stratify patients into those with (IFN-high) or without (IFN-low) an IFN signature. The response of pDC and mDC (in co-culture with T-cells) to IFNα and TLR agonists were analysed by RT-qPCR and flow cytometry to functionally validate RNAseq data.
Results WGCNA identified IFN modules in pDC and mDC that perfectly stratified patients from HC. Comparing the IFN modules of pDC and mDC revealed cell specific alterations related to the IFN signature in pDC/mDC. Increased expression of TLR7 and its downstream intermediates was confined to IFN-high patients in pDC. In contrast, genes involved in the activation of T-cells were related to the IFN module in mDC. Both pDC and mDC showed increased expression of BAFF. In vitro, IFNα upregulated TLR7 in pDC and augmented TLR7-mediated IFNα production. In contrast to pDC, IFNα primed mDC for enhanced T-cell proliferation via the upregulation of co-stimulatory molecules. Furthermore, in SLE/APS, pDC and mDC produced BAFF and expressed chemokine receptors.
Conclusion pDC and mDC are differentially affected by IFNα in SLE and APS. IFNα primes pDC for enhanced IFNα production which potentiates T-cell activation by mDC, thereby sustaining the IFN signature in SLE and APS.
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