<p>(A) Infection by WNV produces dsRNA intermediates within the cytoplasm that display motifs recognized by the RIG-I and MDA5 helicases. Binding of viral RNA promotes an interaction with IPS-1 that results in recruitment of signaling proteins (e.g., NEMO and TRAF3) that lead to activation of IRF-3 and NF-κB. These factors translocate to the nucleus and bind to the promoter region of the IFN-β gene, leading to transcription and translation. In some cells, TLR3 and TLR7 in endosomes recognize dsRNA and ssRNA motifs, leading to recruitment of cytoplasmic adaptor molecules (MyD88 and TRIF), which initiate signaling cascades that activate IRF-3, IRF-7, and NF-κB, resulting in IFN-β gene transcription. Mechanisms of evasion by WNV include the following: (a) reduction in IFN-β gene transcription by the viral NS2A protein; (b) impairment of RIP-1 signaling by high mannose carbohydrates on the structural E protein and attenuation of TLR3 signaling by NS1; and (c) a delay in recognition of WNV RNA by RIG-I. (B) Secretion of IFN by WNV-infected cells results in autocrine and paracrine signaling through the heterodimeric receptor for IFN-α and β (IFNAR). Binding by IFN results in activation and tyrosine phosphorylation of JAK family members (JAK1 and Tyk2) and the cytoplasmic tail of the IFN-αβR. This promotes recruitment of the STAT1 and STAT2, which themselves become phosphorylated by the JAKs. Phosphorylated STAT1 and STAT2 proteins heterodimerize, associate with IRF-9, and translocate to the nucleus, where they bind IFN-stimulated response element (ISRE) sequences to induce expression of hundreds of ISGs. Mechanisms of evasion by WNV include (d) blockade of phosphorylation of Tyk2 and JAK1 by NS5; (e) down-regulation of the IFNAR through virus-induced redistribution of cellular cholesterol; and (f) attenuation of STAT signaling by NS4B.</p
