Toll-like receptor 2; Toll-like receptor 9 (TLR2; TLR9)

Toll-like receptor 2 (TLR2) and Toll-like receptor 9 (TLR9) are type I transmembrane proteins of the toll-like receptor family, essential in innate immunity by recognizing structurally conserved molecules from pathogens. TLR2 is primarily found on cell surfaces and recognizes a broad spectrum of bacterial, fungal, and viral components, while TLR9 is mostly located in endolysosomal compartments and recognizes unmethylated CpG motifs in microbial DNA. Both receptors trigger pro-inflammatory cytokine production through the MyD88-dependent signaling pathway, bridging innate and adaptive immune responses and playing key roles in anti-infective, inflammatory, and autoimmune processes. Both receptors are the focus of intense therapeutic research: TLR9 modulators (such as CpG oligonucleotides) are clinical-stage drug candidates for cancer and infectious diseases, while TLR2 modulation is being studied for vaccine adjuvant effects and as a means of dampening excessive immune responses. Over-activation or dysregulation of either receptor can lead to harmful inflammation or autoimmune pathology, highlighting their therapeutic potential and safety challenges.

Other names

CD282Toll/interleukin-1 receptor-like proteinCD289Cluster of Differentiation 289

Agonists: Activate TLR signaling, leading to NF-κB activation and cytokine release. Antagonists: Block receptor activation to reduce inappropriate inflammation. Some vaccine adjuvants act via TLR2 or TLR9 stimulation to boost immune responses.