Toll-like receptor 3 (TLR3) is also known as CD283, which belongs to the Toll-like receptor family which plays a fundamental role in pathogen recognition and activation of innate immunity. TLRs (Toll-like receptors) control host immune response against pathogens through recognition of molecular patterns specific to microorganisms. TLR3 / CD283 contains 22 LRR (leucine-rich) repeats, 1 LRRCT domain, 1 LRRNT domain and 1 TIR domain. TLR3 is expressed at high level in placenta and pancreas and also detected in CD11c+ immature dendritic cells. CD283 / TLR3 is only expressed in dendritic cells. TLR3 is the TLR that is expressed most strongly in the brain, especially in astrocytes, glia, and neurons. CD283 / TLR-3 is the key component of innate and adaptive immunity. TLR3 / CD283 is a nucleotide-sensing TLR which is activated by double-stranded RNA, a sign of viral infection. TLR3 acts via MYD88 and TRAF6, leading to NF-kappa-B activation, cytokine secretion and the inflammatory response. Defects in TL-R3 are associated with herpes simplex encephalitis type 2 (HSE2).