Epstein-Barr virus (EBV)-encoded small RNAs (EBERs) are nonpolyadenylated, untranslated RNAs, exist most abundantly in latently EBV-infected cells, and are expected to show secondary structures with many short stemloops. Retinoic acid-inducible gene I (RIG-I) is a cytosolic protein that detects viral double-stranded RNA (dsRNA) inside the cell and initiates signaling pathways leading to the induction of protective cellular genes, including type I interferons (IFNs). We investigated whether EBERs were recognized by RIG-I as dsRNA. Transfection of RIG-I plasmid induced IFNs and IFN-stimulated genes (ISGs) in EBV-positive Burkitt's lymphoma (BL) cells, but not in their EBV-negative counterparts or EBER-knockout EBVinfected BL cells. Transfection of EBER plasmid or in vitro-synthesized EBERs induced expression of type I IFNs and ISGs in RIG-I-expressing, EBV-negative BL cells, but not in RIG-I-minus counterparts. EBERs activated RIG-I's substrates, NF-jB and IFN regulatory factor 3, which were necessary for type I IFN activation. It was also shown that EBERs co-precipitated with RIG-I. These results indicate that EBERs are recognized by RIG-I and activate signaling to induce type I IFN in EBV-infected cells.

Epstein-Barr virus–encoded small RNA (EBER) is nonpolyadenylated, noncoding RNA that forms stem-loop structure by intermolecular base-pairing, giving rise to double-stranded RNA (dsRNA)–like molecules, and exists abundantly in EBV-infected cells. Here, we report that EBER induces signaling from the Toll-like receptor 3 (TLR3), which is a sensor of viral double-stranded RNA (dsRNA) and induces type I IFN and proinflammatory cytokines. A substantial amount of EBER, which was sufficient to induce signaling from TLR3, was released from EBV-infected cells, and the majority of the released EBER existed as a complex with a cellular EBER-binding protein La, suggesting that EBER was released from the cells by active secretion of La. Sera from patients with infectious mononucleosis (IM), chronic active EBV infection (CAEBV), and EBV-associated hemophagocytic lymphohistiocytosis (EBV-HLH), whose general symptoms are caused by proinflammatory cytokines contained EBER, and addition of RNA purified from the sera into culture medium induced signaling from TLR3 in EBV-transformed lymphocytes and peripheral mononuclear cells. Furthermore, DCs treated with EBER showed mature phenotype and antigen presentation capacity. These findings suggest that EBER, which is released from EBV-infected cells, is responsible for immune activation by EBV, inducing type I IFN and proinflammatory cytokines. EBER-induced activation of innate immunity would account for immunopathologic diseases caused by active EBV infection.

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Epstein-Barr virus (EBV) infection converts primary human B cells into continuously proliferating lymphoblastoid cell lines (LCLs

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EBV-associated hemophagocytic lymphohistiocytosis (EBV-HLH) is a rare yet devastating disorder caused by EBV infection in humans. However, the mechanism of this disease has yet to be elucidated because of a lack of appropriate animal models. Here, we used a human CD34

We demonstrate here that the Epstein-Barr virus (EBV) BZLF1 gene, a switch from latent infection to lytic infection, is expressed as early as 1.5 h after EBV infection in Burkitt's lymphoma-derived, EBV-negative Akata and Daudi cells and primary B lymphocytes. Since BZLF1 mRNA is expressed even when the cells are infected with EBV in the presence of anisomycin, an inhibitor of protein synthesis, its expression does not require prerequisite protein synthesis, indicating that BZLF1 is expressed as an immediate-early gene following primary EBV infection of B lymphocytes.Epstein-Barr virus (EBV) efficiently infects human B lymphocytes and establishes latent infection, in which the entire EBV genome is maintained as an episome and restricted numbers of EBV genes are expressed (14). EBV binds to B lymphocytes through a direct interaction of the EBV glycoprotein gp350/220 with the complement receptor CD21. Additional interaction of the ternary EBV glycoprotein gp85-gp25-gp42 complex with HLA class II molecules allows endocytosis of the EBV virion into smooth vesicles. Subsequently the viral DNA is transported to the nucleus. The binding of EBV to B lymphocytes induces several signaling pathways that are required for efficient transcription of the viral genome (21). The genes encoding EBV-determined nuclear antigen 2 (EBNA2) and EBNA leader protein are the first viral genes known to be expressed following infection, and both genes have been shown to contribute to the ability of EBV to immortalize primary B lymphocytes (1, 2, 18). Protein synthesis is not required for events leading to the transcription of these genes (18), suggesting that the early stages of infection do not depend on the de novo synthesis of cellular proteins. This is consistent with the Wp promoter, which is constitutively active in B lymphocytes, being the first viral promoter used for transcription of the genes encoding EBNA2 and EBNA leader protein upon infection (26).The BZLF1 protein is a transcriptional activator that binds to AP-1-like motifs in the promoters of early lytic genes (8, 9) and induces lytic infection in latently EBV-infected cells (5, 25). Analysis of Burkitt's lymphoma (BL)-derived Akata cells, in which lytic infection is efficiently and synchronously induced upon cross-linking of cell surface immunoglobulins (Ig) with anti-Ig antibodies, has revealed that BZLF1 is the first gene expressed in the absence of protein synthesis (22,24). Here, we demonstrate that BZLF1 mRNA is expressed as early as 1.5 h postinfection in the absence of protein synthesis in primary EBV infection of B lymphocytes. A possible mechanism of early expression of the BZLF1 gene and its possible role in establishing latent infection are discussed.BL-derived EBV-negative Akata and Daudi cell clones and primary B lymphocytes were used as targets for EBV infection. The Akata and Daudi cell lines were originally EBV positive. As reported previously, we isolated EBV-negative subclones from the parental Akata and Daudi cell cultures by a limitingdilution culture (1...

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