In the early stages of psoriasis (PsO), plasmacytoid dendritic cells (pDCs) are activated by complexes of the antibacterial peptide cathelicidin LL-37 and self-DNA/RNA in a mechanism similar to activation of toll-like receptor 9 (TLR9), which may explain how the host DNA becomes a pro-inflammatory stimulus, breaking the immune tolerance in PsO. Here, TLR9 is linked to psoriasis.