Psoriasis is a complex inflammatory disease resulting from the activation of T helper (Th) 1 and Th17 cells. Recent evidence suggests that abnormal activation of
Toll-like receptors (TLRs) 7, 8 and 9 contributes to the initiation and maintenance of
psoriasis. We have evaluated the effects of TLR antagonists on the gene expression profile in an IL-23-induced skin
inflammation model in mice.
Psoriasis-like skin lesions were induced in C57BL/6 mice by
intradermal injection of
IL-23 in the dorsum. Two TLR antagonists were compared: IMO-3100, an antagonist of TLRs 7 and 9, and
IMO-8400, an antagonist of TLRs 7, 8 and 9, both of which previously have been shown to reduce epidermal
hyperplasia in this model. Skin gene expression profiles of IL-23-induced
inflammation were compared with or without TLR antagonist treatment.
IL-23 injection resulted in alteration of 5100 gene probes (fold change ≥ 2, FDR < 0.05) including
IL-17 pathways that are up-regulated in
psoriasis vulgaris. Targeting TLRs 7, 8 and 9 with
IMO-8400 resulted in modulation of more than 2300 mRNAs while targeting TLRs 7 and 9 with IMO-3100 resulted in modulation of more than 1900 mRNAs. Both agents strongly decreased
IL-17A expression (>12-fold reduction), normalized
IL-17 induced genes such as
beta-defensin and CXCL1, and normalized aberrant expression of
keratin 16 (indicating epidermal
hyperplasia). These results suggest that IL-23-driven
inflammation in mouse skin may be dependent on signaling mediated by TLRs 7, 8, and 9 and that these receptors represent novel therapeutic targets in
psoriasis vulgaris and other diseases with similar pathophysiology.