TLR expression in human melanoma cells

There is increasing evidence that melanoma cells express TLR2, -3, and -4. However, the expression of other TLRs by these cells still remains unknown. We investigated the expression patterns of TLR2, -3, -4, -7, -8 and -9 both on melanoma-invaded lymph nodes and on melanoma cell lines. TLR2, -3, -4, -7 and -9 mRNA expression was determined by quantitative RT-PCR. The TLR protein expression level was measured ex vivo by immunohistochemistry and in vitro by flow cytometry. Results: At the mRNA level, melanoma cells in vitro, and possibly ex vivo, expressed TLR2, -3, -4, -7 and -9. TLR2 and -4 protein expressions ex vivo were over 50%, contrasting with an absence of these 2 TLRs in vitro. On the contrary, TLR-3 and -8 proteins had a low expression ex vivo with a high expression in vitro. TLR-7 and -9 proteins were expressed ex vivo and in vitro. Our study demonstrates for the first time that melanoma cells express TLR7 and -8.