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Aims--Post-transplant lymphoproliferative disease (PTLD) is an important and serious complication in transplant patients. Recent studies have suggested that quantitative assessment of Epstein-Barr virus (EBY) infection in transplant patients might help to identify those at risk of developing PTLD. Therefore, tonsils from paediatric liver transplant recipients were studied for evidence of EBV infection.
Methods--Tonsils were studied by in situ hybridisation for the detection of the small EBV encoded nuclear RNAs (EBERs). The phenotype of EBV infected cells was determined by double labelling in situ hybridisation and immunohistochemistry. The expression of viral latent and lytic antigens was determined by immunohistochemistry. Tonsils from patients without known immune defects were studied as controls.
Results--Tonsils from transplant patients showed pronounced follicular hyperplasia and minor paracortical hyperplasia. In situ hybridisation revealed variable numbers of EBV infected B cells in the tonsils from transplant patients (range, 2-10001 0.5 [cm.sup.2]; mean, 43410.5 [cm.sup.2]; median, 105/ 0.5 [cm.sup.2]). Lower numbers were detected in the control tonsils (range, 1-200/0.5 [cm.sup.2] mean, 47/0.5 [cm.sup.2]; median, 9/0.5 [cm.sup.2]). The latent membrane protein 1 (LMP1) of EBV was not detected and there were only rare cells in two cases showing expression of the EBV encoded nuclear antigen 2 (EBNA2). There was no evidence of lytic infection. None of the patients developed PTLD within a follow up period of up to five years.
Conclusions--These data indicate that tonsillar enlargement in paediatric liver transplant patients does not necessarily imply a diagnosis of PTLD. Furthermore, the presence of increased numbers of EBV infected cells in tonsils from liver transplant recipients by itself does not indicate an increased risk of developing PTLD.
(J Clin Pathol: Mol Pathol 2001;54:264-269)
Keywords: Epstein-Barr virus; transplantation; lymphoproliferative disease; tonsil
Epstein-Barr virus (EBV) associated post-transplant lymphoproliferative disease (PTLD) is an important complication in transplant patients.  The risk of developing PTLD is variable depending, among others, on the nature of the transplanted organ and on the level of iatrogenic immunosuppression.  In general, patients undergoing primary EBV infection after transplantation and those treated with anti-T cell reagents are particularly at risk.  The incidence of PTLD is higher in paediatric patients than in adults.  The disease frequently involves Waldeyer's ring.  PTLDs are usually of B cell lineage, and include a spectrum of disorders ranging from polyclonal polymorphic lymphoproliferations to monoclonal non-Hodgkin's lymphoma.  The prognosis of PTLD remains poor and treatment is controversial. 
Suppression of EBV specific T cell immunity is thought to be the central factor in the pathogenesis of PTLD, allowing the outgrowth of an initially polyclonal B cell population. Through the acquisition of additional genetic alterations, such as c-myc translocations or p53 mutations, this is believed to give rise to fully malignant monoclonal lymphonmas.  In support of this model, reduction or withdrawal of the immunosuppressive treatment has been reported to result in a spontaneous remission of some cases of PTLD.  In addition, successful prevention or treatment of PTLD has been demonstrated by the infusion of EBV specific cytotoxic T cells (CTLs).  Alternatively, the application of B cell specific monoclonal antibodies has been used successfully for the treatment of PTLD .  Early detection of PTLD or identification of patients at risk of developing PTLD is clearly important because therapeutic approaches aimed at modifying the EBV specific immunity are likely to be more successful in early stage s of the disease. It has been suggested that PTLD in paediatric liver transplant recipients may frequently localise to the tonsils and may be diagnosed by tonsillar biopsy.  It has also been reported that the detection of EBV positive B cells in liver transplant biopsy specimens by in situ hybridisation (ISH) may indicate a risk of PTLD,  but this has not been confirmed …