TLR9 and psoriasis: The TT genotype polymorphism of TLR9, a TLR found on pDCs, was strongly associated with a high (>10) Psoriasis Area Severity Index (PASI), and the TT genotype also showed decreased responsiveness to standard narrow-band ultraviolet B light therapy when compared to TC and CC genotype polymorphisms of TLR9 [2,20].