Immunological responses to Epstein-Barr virus infection and the pathogenesis of EBV-induced diseases

Evaluation of use of Epstein-Barr viral load in patients after allogeneic stem cell transplantation to diagnose and monitor posttransplant lymphoproliferative disease

Epstein-Barr virus (EBV)-induced posttransplant lymphoproliferative disease (PTLD) continues to be a serious complication following transplantation. The aim of the present study was to evaluate the EBV load as a parameter for the prediction and monitoring of PTLD. The EBV load was analyzed by a quantitative competitive PCR with 417 whole-blood samples of 59 patients after allogeneic stem cell transplantation (SCT). The EBV load was positive for all 9 patients with PTLD and for 17 patients without PTLD. The viral loads of patients with manifest PTLD differed from the loads of those without PTLD (median loads, 1.4 x 10(6) versus 4 x 10(4) copies/microg of DNA; P < 0.0001). A threshold value of 10(5) copies/microg of DNA showed the best diagnostic efficacy (sensitivity, 87%; specificity, 91%). However, in patients with less than three major risk factors for PTLD, the positive predictive value of this threshold was rather low. One week prior to the manifestation of PTLD, the EBV load was as low in patients who developed PTLD as in patients without disease (median, 2.2 x 10(4) copies/microg of DNA; P was not significant). EBV DNA tested positive first at 20 to 71 days prior to the clinical manifestation of PTLD and occurred with the same delay after transplantation regardless of disease (median delay, 52 versus 63 days; P was not significant). EBV DNA was detected earlier in patients with primary infections than in those with reactivations (33 versus 79 days; P = 0.01), but the peak levels were similar in the two groups. EBV primary infection or EBV reactivation is frequent in patients after allogeneic SCT but results in PTLD only in a subgroup of patients. Although evaluation of the EBV load has limitations, the EBV load represents a valuable parameter to guide therapy.

Detection of Epstein-Barr virus DNA in sera from transplant recipients with lymphoproliferative disorders

Early diagnosis of Epstein-Barr Virus (EBV)-associated posttransplant lymphoproliferative disease (PTLD) is important because many patients respond to reduction in immunosuppression, especially if PTLD is detected at an early stage. Previous studies have found elevated EBV DNA levels in blood from patients with PTLD, but these assays required isolation of cellular blood fractions and quantitation. We evaluated the presence of cell-free EBV DNA in serum from solid-organ transplant recipients as a marker for PTLD. Five of 6 transplant recipients with histopathologically documented PTLD had EBV DNA detected in serum at the time of diagnosis (sensitivity = 83%), compared with 0 of 16 matched transplant recipients without PTLD (specificity = 100%) (P < 0.001 [Fisher's exact test]). Furthermore, EBV DNA was detected in serum 8 and 52 months prior to the diagnosis of PTLD in two of three patients for whom stored sera were analyzed. Detection of EBV DNA in serum appears to be a useful marker for the early detection of PTLD in solid-organ transplant recipients. Further studies to define the role of such assays in evaluating solid-organ transplant patients at risk for PTLD are warranted.

Identification of the site of Epstein-Barr virus persistence in vivo as a resting B cell

Epstein-Barr (EBV) is a powerful immortalizing virus for human B lymphocytes in vitro and is associated with several human neoplasias in vivo. Previously, we have shown that the majority of EBV-infected cells in the peripheral blood of healthy, persistently infected individuals do not express the activated phenotype, e.g., high levels of cell surface CD23 and CD80 (B7), characteristically expressed on in vitro-immortalized cells. Here, we show that > or = 90% of the CD23-, virus-infected cells in the peripheral blood are in G0 and therefore resting. The remaining cells may be G1 arrested, but we were unable to detect a significant number of cells traversing the S-G2-M stages of the cell cycle. The mRNA for LMP2A, but not EBNA1 originating from Qp, was readily detected in this population, and these cells appear competent in the processing and presentation of antigen by class I major histocompatibility complex. We propose that these resting B cells are the site of long-term latent persistence for EBV. We further propose that the persistence of the virus in a resting B7- B cell provides an important mechanism to escape immunosurveillance. The demonstration that EBV can persist latently in a resting B cell means that the immortalizing functions of EBV can be down regulated in a normal B cell. This conclusion has important implications for understanding and controlling EBV-associated neoplasia.

Epstein-Barr virus (EBV) infects T lymphocytes in childhood EBV-associated hemophagocytic syndrome in Taiwan

We have reported the prevalence of a fulminant hemophagocytic syndrome (HS) in previously healthy young children in Taiwan, most of which probably represent a lethal form of primary or active Epstein-Barr virus (EBV) infection. To further confirm their EBV association, in situ EBV hybridization (ISH) was performed on tissue biopsies from 15 pediatric HS patients (median age, 3 years and 4 months) using digoxigenin-labeled RNA probes EBER1. Double labeling immunostaining and ISH was then performed to define the immunophenotype of the lymphoid cells containing the EBV transcripts. Among the 13 patients who had serological evidence of acute or active EBV infection, 9 had demonstrable EBER1 transcripts in bone marrow, liver, and/or skin biopsies. EBER1-specific signal was not detectable in the two specimens from EBV-seronegative patients. The distribution of EBV-containing cells could be extensive or scattered. To our surprise, the EBER1 transcripts existed exclusively in T lymphoid cells in all nine cases examined rather than in B cells as previously believed in infectious mononucleosis. Considering the young affected age of the HS patients and the serological response to EBV, we suggest that EBV can infect T cells in primary EBV infection and the proliferation of these EBV-infected T cells may be responsible for the ominous outcome in childhood HS patients in Taiwan.

Detection of single copies of Epstein-Barr virus in paraffin wax sections by non-radioactive in situ hybridisation

A highly sensitive non-isotopic in situ hybridisation technique was developed for the localisation of Epstein-Barr virus (EBV) in paraffin wax embedded tissue sections. The method uses a repeated sequence of the EBV genome as a probe, labelled with the novel reporter molecule, digoxigenin. The method can identify individual copies of EBV by detection of both EBV DNA and highly localised RNA transcripts. A combination of careful proteolytic digestion of tissue sections, high temperature denaturation of probe and target DNA, and sensitive immunocytochemical detection are used to attain single copy sensitivity. The technique is quicker and simpler to perform than some other methods used for the identification of EBV, and provides simultaneous morphological information which cannot be obtained by methods using tissue extracts. This method permits the investigation of the role of EBV in neoplastic conditions of lymphoid and epithelial cells, and may prove valuable in determining the sites of latent virus in healthy subjects.