Toll-like receptor 7; Toll-like receptor 9 (TLR7; TLR9)

Toll-like receptor 7 and toll-like receptor 9 are pattern recognition receptors of the innate immune system, classified within the Toll-like receptor family. TLR7 primarily resides in the endosomal compartments of immune cells such as macrophages and dendritic cells, where it detects viral single-stranded RNA and triggers an antiviral immune response through type I interferon and pro-inflammatory cytokine secretion. TLR9, similarly localized to endosomes in dendritic cells, recognizes unmethylated CpG motifs in microbial DNA, activating both innate and adaptive immunity. Both receptors function via the MyD88-dependent signaling pathway—ligand binding induces receptor dimerization and subsequent assembly of multi-protein complexes (Myddosome), leading to NF-κB and IRF7 activation. These pathways are essential for early defense against infections, but dysregulation can contribute to inflammation, autoimmunity, and cancer. Pharmacological targeting of TLR7 and TLR9 includes the use of specific agonists (e.g., imiquimod, CpG oligonucleotides) and antagonists for therapeutic modulation of immune responses in infections, cancer, and autoimmunity.

Other names

TLR7: Toll-like receptor 7TLR9: Toll-like receptor 9Alternative names not frequently used for these, though gene names (e.g., TLR7 gene, TLR9 gene) occasionally appear

Agonists: ligand binding causes receptor dimerization and transition into a signaling-competent "closed" conformation, activating MyD88-dependent pathway, leading to NF-κB activation, cytokine secretion, and interferon production. Antagonists: prevent dimerization or stabilize the "open" (inactive) conformation, inhibiting downstream signaling. CpG oligos (for TLR9): induce type I interferon response and pro-inflammatory cytokines via MyD88, IRAK4, TRAF6, IRF7 activation.