Psoriasis is triggered by some external factors, such as mechanical stimuli (isomorphic response of Köbner), followed by a complex of self-DNA/RNA and cathelicidin(LL37) incorporated into plasmacytoid dendritic cells (pDCs), which then upregulates toll-like receptor-7 (TLR-7) and -9, leading to production of large amounts of interferon (IFN)-α. The gene discussed is TLR7; the disease is psoriasis.