Toll-like receptor 2 mediates a cutaneous reaction induced by repetitive ultraviolet b irradiation in C57/BL6 mice in vivo

A) Background: Toll like receptors (TLR) are a family of pattern recognition receptors that play an essential role in the induction of the immune response activated not only via microbial infection, but also via endogenous molecules released from non-infectious inflammatory processes such as tissue injury. Previous studies suggested that single ultraviolet (UV) exposure may also initiate a TLR-mediated non-infectious and sterile inflammation in vitro.

B) Methods: Inflammatory responses to repetitive UBV irradiation were compared between wild-type (WT) and TLR2 knock-out (KO) mice.

C) Results: After 6 weeks of repetitive UVB irradiation, inflammatory response of the TLR2 KO group was less severe than that of the TLR2 WT group. Compared to the group of TLR2 WT mice, the group of TLR2 KO mice displayed less prominent erythema and scaling; and histopathologically fewer inflammatory cells and significantly thinner skin. UVB-induced expression of the heat shock protein 70, an endogenous ligand of TLR2, was lower in the TLR2 KO group. Quantitative RT-PCR was used to measure the gene expression levels of interleukin (IL)-1β, IL-6, and matrix metalloproteinase (MMP)-13, all of which were considerably lower in the TLR2 KO group, compared to the WT group. This finding was further corroborated with ELISA and western blot, each of which showed lower protein expression level of IL-1β, and MMP-13, respectively.

D) Conclusion: This study demonstrated that TLR2 is involved in cutaneous inflammatory reaction to repetitive UV irradiation in C57/B16 mice.