Epstein-Barr virus-infected B cells in vivo demonstrate three distinct patterns of latent gene expression, depending on the differentiation stage of the cell. Tonsillar naive B cells express the EBNA2-dependent lymphoblastoid phenotype, characteristic of direct infection. Germinal center centroblasts and centrocytes as well as tonsillar memory B cells express a more restricted pattern of latent genes (EBNA1(Q-K)+, LMP1+, LMP2+, EBNA2-) that has only been seen previously in EBV-positive tumors. Peripheral memory cells express an even more restricted pattern where no latent genes are expressed, with the possible exception of LMP2. These results are consistent with a model where EBV uses the normal biology of B lymphocytes to gain access to and persist within the long-lived memory B cell compartment.

Epstein-Barr virus (EBV) is a herpesvirus that establishes a lifelong, persistent infection.It was first discovered in the tumor Burkitt's lymphoma (BL). Despite intensive study, the role of EBV in BL remains enigmatic. One striking feature of the tumor is the unique pattern of viral latent protein expression, which is restricted to EBV-encoded nuclear antigen (EBNA) 1. EBNA1 is required to maintain the viral genome but is not recognized by cytotoxic T cells. Consequently, it was proposed that this expression pattern was used by latently infected B cells in vivo. This would be the site of long-term, persistent infection by the virus and, by implication, the progenitor of BL. We now know that EBV persists in memory B cells in the peripheral blood and that BL is a tumor of memory cells. However, a normal B cell expressing EBNA1 alone has been elusive. Here we show that most infected cells in the blood express no detectable latent mRNA or proteins. The exception is that when infected cells divide they express EBNA1 only. This is the first detection of the BL viral phenotype in a normal, infected B cell in vivo. It suggests that BL may be a tumor of a latently infected memory B cell that is stuck proliferating because it is a tumor and, therefore, constitutively expressing only EBNA1.

We have proposed that EBV uses mature B cell biology to access memory B cells as a site of persistent infection. A central feature of this model is that EBV adapts its gene expression profile to the state of the B cell it resides in and that the level of infection is stable over time. This led us to question whether changes in the behavior or regulation of mature B cells would alter the state of EBV persistence. To investigate this, we studied the impact of systemic lupus erythematosus (SLE), a disease characterized by immune dysfunction, on EBV infection. We show that patients with SLE have abnormally high frequencies of EBV-infected cells in their blood, and this is associated with the occurrence of SLE disease flares. Although patients with SLE have frequencies of infected cells comparable to those seen in immunosuppressed patients, in SLE the effect was independent of immunosuppressive therapy. Aberrant expression of viral lytic (BZLF1) and latency (latency membrane proteins 1 and 2a) genes was also detected in the blood of SLE patients. We conclude that the abnormal regulation of EBV infection in SLE patients reflects the sensitivity of the virus to perturbation of the immune system.

In this paper we demonstrate that during acute infection with Epstein-Barr virus (EBV), the peripheral blood fills up with latently infected, resting memory B cells to the point where up to 50% of all the memory cells may carry EBV. Despite this massive invasion of the memory compartment, the virus remains tightly restricted to memory cells, such that, in one donor, fewer than 1 in 10 4 infected cells were found in the naive compartment. We conclude that, even during acute infection, EBV persistence is tightly regulated. This result confirms the prediction that during the early phase of infection, before cellular immunity is effective, there is nothing to prevent amplification of the viral cycle of infection, differentiation, and reactivation, causing the peripheral memory compartment to fill up with latently infected cells. Subsequently, there is a rapid decline in infected cells for the first few weeks that approximates the decay in the cytotoxic-T-cell responses to viral replicative antigens. This phase is followed by a slower decline that, even by 1 year, had not reached a steady state. Therefore, EBV may approach but never reach a stable equilibrium.The B-lymphotropic herpesvirus Epstein-Barr virus (EBV) is a ubiquitous human virus (reviewed in references 23 and 45) that establishes a lifelong persistent infection in memory B lymphocytes (3). It is an important pathogen because of its association with several human neoplasias (reviewed in references 38 and 45). However, no good animal model exists for the study of EBV. The murine gammaherpesvirus 68 (MHV68) is a related virus which has tropism for B lymphocytes (44) and also persists in memory B cells (12, 50). However, it appears to lack the specific latency transcription programs of EBV and persistence is not dependent on B lymphocytes (49). Primate homologues of EBV are known (7,11,42), but these are not useful because of financial constraints and the lack of virological and immunological reagents for these systems. Despite this limitation, EBV has emerged as an excellent system for studying persistent infection in humans. There are two primary reasons for this. First, EBV infects resting B cells in culture and transforms them into continuously proliferating, latently infected lymphoblasts (35,36). This provides a readily manipulable in vitro system for studying the functions of the latency-associated proteins. Second, the major sites of viral persistence, the peripheral blood and Waldeyer's ring (29), are relatively accessible for study. Taking together information from both in vitro and in vivo studies we have developed a unified model of how EBV establishes and maintains a persistent infection (46) (Fig. 1). The key underlying theme of the model is that EBV uses its latent proteins to provide signals to the infected B cell that cause it to become activated and then differentiate, through a mechanism analogous to the germinal center reaction (30, 31), into a resting memory cell. We have provided evidence that these events occur in the lymphoid tissue o...