Plasmacytoid dendritic cells (pDCs) are the dominant acute source of type I IFNs (particularly IFN-α) following endosomal TLR7/9 ligation, and they orchestrate the systemic “IFN-high” endotype seen in lupus and related conditions [81,82]. This evidence concerns the gene TLR7 and systemic lupus erythematosus.