UNC93B is a protein of the endoplasmic reticulum involved in Toll-receptor activation. Mutation in UNC93B impair the production of INF-α and IFN-β in response to HSV and other viruses. Affected patients present with Herpes simplex viral encephalitis. Recently, heterozygous dominant-negative mutations in the gene encoding toll receptor 3 (TLR4) have been identified in patients with Herpes simplex encephalitis. TLR3 is expressed in the central nervous system where it helps to initiate IFN-α and IFN-β responses to viral double-stranded DNA.