Toll-like receptor 6 (TLR6) participates in the innate immune response to Gram-positive bacteria and fungi. TLRs recognize specific molecular patterns present only in micro-organisms. TLR1 and TLR6 are involved in the discrimination of a subtle difference between triacyl and diacyl lipopeptides through interaction with TLR2 []. Cooperatively with TLR2, TLR6 recognises mycoplasmal macrophage-activating lipopeptide-2 (MALP-2), soluble tuberculosis factor (STF), phenol-soluble modulin (PSM) and Borrelia burgdorferi outer surface protein A lipoprotein (OspA-L) []. TLR6 acts via MYD88 and TRAF6, leading to NF-kappa-B activation, cytokine secretion and the inflammatory response [].
Toll-like receptor 2 (TLR2) is a member of the Toll-like receptor (TLR) family, which plays a role in activation of innate immunity and pathogen recognition []. It helps mediate the innate immune response to bacterial lipoproteins and other microbial cell wall components, acting via MyD88 and TRAF6, leading to NF-kappa-B activation, cytokine secretion and the inflammatory response [, , , ]. TLR2 in association with TLR1 or TLR6 is essential for recognising bacterial lipoproteins and lipopeptides [, ]. It also promotes apoptosis in response to lipoproteins [].Genetic variations in TLR2 are associated with susceptibility to leprosy, a chronic disease associated with depressed cellular (but not humoral) immunity [, ].
This entry represents toll-like receptors (TLRs), which are key regulators of immune responses. They recognise pathogen-associated molecular patterns (PAMPs) such as bacterial lipopeptides (TLR1/2/6), bacterial flagellin (TLR5), and lipopolysaccharide (TLR4) []. In highervertebrates, TLRs are essential not only for sensing microbes by the innate immune system, but also for inducing adaptive immune system responses mediated by B and T cells [].TLRs are expressed at the cell membrane and in subcellular compartments such as the endosome. TLRs are type-I transmembrane proteins with extracellular leucine-rich repeat (LRR) motifs and an intracellular Toll/interleukin-1 receptor (TIR) domain. Members of the TLR family contribute both to cell-cell interactions and to signalling, linking extracellular signals to specific gene-expression programmes [, ]. Binding of ligands to the extracellular domains causes rearrangement of the receptor complexes and triggers the recruitment of specific adaptor proteins to the intracellular TIR domain, leading to nuclear factor-kappa B (NF-kappaB) activation and initiation of both innate and adaptive immune responses. Signalling by TLRs involves five adaptor proteins known as MyD88, MAL, TRIF, TRAM and SARM []. TLRs form homodimers or heterodimers induced by the binding of ligands to residues in the LRRs of distinct receptor chains. In mice and humans combined there are 13 paralogous TLRs; 10 in humans and 12 in mice. TLR10 is only present in humans, and TLR11-13 are only present in mice []. This entry represents some toll-like receptors, which includes TLR1, TLR2, TLR4, TLR5, TLR6 and TLR10.In Drosophila, the Toll receptor plays a role in development as well as immunity [, ]. Toll is a component of the extracellular signaling pathway that establishes the dorsal-ventral pathway of the embryo []. Three proteases; ndl, gd and snk process easter to create active easter. Active easter defines cell identities along the dorsal-ventral continuum by activating the Spz ligand for the Tl receptor in the ventral region of the embryo []. Toll promotes heterophilic cellular adhesion []. The Drosophila Toll receptor is essential in initiating innate immune defenses to fungi and Gram-positive bacteria in adult flies []. Spz C-106 in the hemolymph controls expression of the antifungal peptide Drosomycin (Drs) by acting as a ligand of Tl and inducing an intracellular signaling pathway [].
