TLR5 is a member of the toll-like receptor (TLR) family, which plays a fundamental role in pathogen recognition and activation of innate immune responses. These receptors recognize distinct pathogen-associated molecular patterns that are expressed on infectious agents. The protein encoded by this gene recognizes bacterial flagellin, the principal component of bacterial flagella and a virulence factor. The activation of this receptor mobilizes the nuclear factor NF-kB, which in turn activates a host of inflammatory-related target genes. Mutations in this gene have been associated with both resistance and susceptibility to systemic lupus erythematosus, and susceptibility to Legionnaire disease. Placental alkaline phosphatase is one of the most stable isoenzyme, only existing in the placenta of higher primates. These characteristics make placental alkaline phosphatase suitable to use as a reporter gene for the analysis of promoter activity and gene expression in cell culture and animal serum. The natural form of placental alkaline phosphatase (PLAP) is membrane anchored. The recombinant form of placental alkaline phosphatase (secreted alkaline phosphatase, SEAP) is used for reporter gene function. SEAP is created by inserting a translational terminator after amino acid 489 (Berger, et al., Gene 66 : 10. This mutation converts the membrane-bound PLAP protein into the secreted protein. As a major transcription factor, NF-kB plays a key role in regulating genes responsible for the innate and adaptive immune responses. In unstimulated cells, the NF-kB dimers are held in the cytoplasm by IkBs that masks the nuclear localization signals of NF-kB. Upon cell stimulation, which leads to IkB degradation, NF-kB quickly translocates to the nucleus and activates various genes that have DNA-binding sites for NF-kB.