The majority of tumours in endemic form of BL contain EBV DNA sequences. In addition, malaria P. falciparum infection occurs co-incidentally. Malaria infection is thought to depress cytotoxic T-cell function, thus rendering the patient relatively cytotoxic T-cell deficient and allowing the EBV infection to escape T-cell surveillance. The role of EBV in non-endemic and AIDS-related BL is complex and less definitive. EBV DNA is detectable in only 10-15% of patients with non-endemic BL and 50% of patients with AIDS-related BL. Immunoblastic lymphomas associated with chronic immunosuppression in allograft recipients or AIDS patients and undifferentiated NPC invariably contain EBV DNA sequences. In Hodgkin's disease, 50% of tumours contain EBV-infected cells and, in addition, the EBV genome has been demonstrated in the Reed-Sternberg cells of Hodgkin's disease.
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