Expression and Function of Toll-Like Receptor 2 and 4 in Human Melanocytes

Abstract

Toll-like receptors (TLRs) are crucial players in the innate immune response to microbial invaders. There have been reported that keratinocyte TLRs represent the first barrier against exogenous pathogens in human skin. Recently, it was reported that melanocytes not only function melanin synthesis but also act as immunocompetent cell. Melanosome and melanin in melanoyctes have antimicrobial function. In this study, we focused that microbial induced pigmentation may be related to TLRs in human skin. Therefore we investigated whether TLRs are expressed in melanocytes and played a role in microbial-induced melanogenesis. First, the mRNA expression of TLR2, TLR4 and their adaptor proteins, CD14 and myeloid differentiation factor-88 (MyD88) was shown by RT-PCR. Protein expression and localization of TLR2, TLR4 and CD14 were detected by western blot, flow cytometry and immunocytochemistry. Lipopolysaccharide (LPS) was used as microbial stimulator on melanocytes. The expression of TLR2, TLR4 and MyD88 at mRNA and protein level were increased after LPS stimulation. LPS affected cell proliferation and melanin synthesis. TLR2 expression was decreased in vitiligo lesion compared with normal skin. These findings suggested that TLR2 and TLR4 may play a role in the microbial-induced melanogenesis.