Biol. Pharm. Bull. 28(5) 886—892 (2005)

ated molecular patterns, play important roles in innate immunity in mammals. Recently, at least 10 members of the TLR family have been identified, and several ligands recognized by TLRs have been reported. Triacylated bacterial lipopeptides are recognized by the cooperation of TLR2 with TLR1. It has been reported that TLR1 coexpression inhibits the TLR2-mediated response to phenol-soluble modulin, a factor secreted by Staphylococcus epidermidis, while coexpression with TLR6 enhances the TLR2 response. TLR3 recognizes the double-stranded RNA produced by most viruses during replication. TLR4 is an essential receptor that transduces the signals of lipopolysaccharide (LPS). The innate immune response to bacterial flagellin is mediated by TLR5. TLR7 recognizes the single-stranded RNA (ssRNA) viruses, vesicular stomatitis virus and influenza virus. Heil et al. reported that ssRNA represents a physiological ligand for murine TLR7 and human TLR8. TLR9 recognizes unmethylated CpG DNA found in bacteria. The specific ligands and functions of TLR10 are currently obscure, although it is known to be expressed in the spleen and lung. It has been reported that the TLRs collaborate with many molecules such as MyD88, MD-2, TICAM, TIRAP, IRAK, TRAF6, etc. The nomenclature for these TLRs and related genes is summarized in Table 1. The tissue distributions of many TLRs and related genes such as MyD88 and TICAM2 have been reported. Information concerning gene expression in various tissues and cell lines may be important in assessing the feasibility of measuring the mRNA expression level of target genes in target tissues and cell lines. However, the tissue distribution of the mRNA expression of large numbers of human TLRs and related genes has not been evaluated under the same experimental conditions. The present study was therefore undertaken to investigate the mRNA expression levels of 10 human TLRs and 21 related genes (ICAM1, CD14, MyD88, LY96, TRIF, TICAM2, TIRAP, CD80, CD83, CD86, SOCS1, TNFAIP3, TOLLIP, IRAK1, IRAK2, IRAK3, IRAK4, TRAF6, CCL2, CCL5, and CXCL10) using high-sensitivity real-time reverse transcription PCR (RT-PCR) in total RNA from pooled specimens of 2 fetal human tissues, from single and pooled specimens of 18 adult human tissues, and from 2 cell lines.