Recombinant Mouse TLR5 Fc Chimera Protein, CF

TLR5 (Toll-like receptor 5) is an approximately 100 kDa cell surface type I transmembrane glycoprotein of the TLR family of pathogen‑associated molecular pattern (PAMP) receptors (1‑3). TLR5 recognizes flagellins, proteins found on flagella of both gram‑positive and gram‑negative pathogenic bacteria (2, 3). The 859 amino acid (aa) mouse TLR5 precursor includes a 21 aa signal sequence, a 621 aa extracellular domain (ECD) with 9 potential N‑glycosylation sites and 16 leucine‑rich repeats (LRR) that contain the flagellin‑binding site, a transmembrane domain, and a 197 aa cytoplasmic region with a TIR (Toll/ IL-1 R) domain (1, 4). The mouse TLR5 ECD shares 84% aa sequence identity with rat and 69‑73% with human, feline, porcine and bovine TLR5. TLR5 is expressed on mucosal epithelia in the gastrointestinal tract, airways, and other areas of potential contact with bacteria, and on alveolar macrophages, monocytes, neutrophils, CD4⁺ T lymphocytes, and dendritic cell subsets (3‑7). In some portions of the intestine, epithelial TLR5 is expressed only on the basolateral surface (3, 4). Flagellin engagement induces signaling via direct interaction of TLR5 with MyD88, which activates NFkB and stimulates production of inflammatory cytokines such as TNF‑ alpha, IL‑1 beta, IL‑6 and IL‑8, depending on the cell type (2‑6, 8, 9). TLR5 allows recognition of pathogenic bacteria such as Pseudomonas, Salmonella and Listeria, without reaction to non‑flagellated commensal bacteria (3, 4). It stimulates massive neutrophil recruitment and EGF R‑mediated mucus production by airway epithelia (4, 9, 10). It promotes Th2 polarization and IgA secretion, and restrains local regulatory T cell generation (4, 7). Deletion of mouse TLR5 promotes colitis, probably due to TLR4‑mediated inappropriate responses to commensal bacteria (11).