Epstein-Barr virus infection after pediatric living-related liver transplantation--management and risk factors.

INTRODUCTION: Posttransplant lymphoproliferative disorder (PTLD) is one of the severe complications after pediatric liver transplantation. Epstein-Barr virus (EBV) infection is a major risk factor developing PTLD. This study evaluates the risk factors, incidence, and clinical presentation of EBV infection at our institute. PATIENTS AND METHODS: This study examines 81 children who underwent living-related liver transplantation (LRLT) from November 2005 to December 2009. The immunosuppression protocol consisted of tacrolimus and low-dose steroids, which were withdrawn by 3 months after LRLT. Additional immunosuppression was indicated for the selected cases because of recurrent rejection or renal insufficiency. Fifteen ABO blood type incompatible LRLTs were enrolled into this study. EBV was periodically monitored by the use of a real-time quantitative polymerase chain reaction (cut-off value, >10(2) copies/µg DNA). The median follow-up period was 637 days (range, 85 to 1548 days). These patients were divided into two groups: EBV infection versus EBV noninfection, for analysis of risk factors by univariate analysis. RESULTS: The incidence of EBV infection was 50.6% (n = 41) with the mean onset of 276 ± 279 postoperative days (range, 7 to 1229 days). Nine cases (22.5%) presented clinical symptoms related to EBV infection, consisting of adenoid hypertrophy (n = 5), Evans's syndrome (n = 2), hemophagocytic syndrome (n = 1), and erythema nodosum (n = 1). There was no case of PTLD. The combination of a preoperative EBV seropositive donor and an EBV seronegative recipient was a high risk factor for postoperative EBV infection among the recipients (56.1% versus 26.8%, P < .05). The mean age at operation among the EBV infection group was younger than that of the EBV noninfection group (22 ± 30 months versus 62 ± 68 months; P < .05). The incidence of acute rejection episodes and cytomegalovirus infections; ABO blood type incompatible LRLT, and the length of steroid treatment and the additional immunosuppression were not significantly different between the two groups. CONCLUSION: There were various clinical presentations related to EBV infection; however, none of our patients developed PTLD. Careful monitoring of EBV infection especially for cases with donor seropositivity is important to prevent disease progression.

Activation of TRAF5 and TRAF6 signal cascades negatively regulates the latent replication origin of Epstein-Barr virus through p38 mitogen-activated protein kinase.

Latent Epstein-Barr virus (EBV) is maintained by the virus replication origin oriP that initiates DNA replication with the viral oriP-binding factor EBNA1. However, it is not known whether oriP's replicator activity is regulated by virus proteins or extracellular signals. By using a transient replication assay, we found that a low level of expression of viral signal transduction activator latent membrane protein 1 (LMP1) suppressed oriP activity. The binding site of the tumor necrosis factor receptor-associated factor (TRAF) of LMP1 was essential for this suppressive effect. Activation of the TRAF signal cascade by overexpression of TRAF5 and/or TRAF6 also suppressed oriP activity. Conversely, blocking of TRAF signaling with dominant negative mutants of TRAF5 and TRAF6, as well as inhibition of a downstream signal mediator p38 MAPK, released the LMP1-induced oriP suppression. Furthermore, activation of TRAF6 signal cascade by lipopolysaccharides (LPS) resulted in loss of EBV from Burkitt's lymphoma cell line Akata, and inhibition of p38 MAPK abolished the suppressive effect of LPS. These results suggested that the level of oriP activity is regulated by LMP1 and extracellular signals through TRAF5- and TRAF6-mediated signal cascades.

Requirement of replication licensing for the dyad symmetry element-dependent replication of the Epstein-Barr virus oriP minichromosome.

Latent Epstein-Barr virus genome is maintained in cells by the viral oriP-binding factor EBNA1 and cellular replication factors. EBNA1 binds to the dyad symmetry (DS) element in oriP and initiates DNA replication once in a single S phase, but the mechanism by which this DS-dependent replication is initiated is unknown. Replication licensing of cellular chromatins occurs during early G1 phase. Because licensing is essential for the next round of replication in S phase, it facilitates once-in-a-cell-cycle replication of the cellular genome. Using the transient replication assay with HeLa/EB1 cell, we demonstrate that the oriP plasmid required a cell cycle window including early G1 phase for replication in the next S phase. The plasmid containing only the DS element had a similar requirement of early G1 phase for replication. Analysis using sucrose density gradient centrifugation revealed that the oriP minichromosome existed in two distinct states: one formed at late G1 and the other formed at G2/M. These results suggest that the DS-dependent DNA replication from oriP requires the replication licensing, implying a possible involvement of the cellular licensing factor MCM in the DNA replication from oriP.