Epstein-Barr virus-infected T cells in infectious mononucleosis.

Epstein-Barr virus (EBV) has been known as a B cell lymphotropic virus since the initial discovery of this virus in the cell lines established from Burkitt’s lymphoma (BL).’ EBV has been shown to cause infectious mononucleosis (IM), to be associated with BL and nasopharyngeal carcinoma, and to be linked to other neoplasms and polyclonal lymphoproliferative disorders in immunocompromized individuak2 EBV infects B lymphocytes by attachment to a cell surface receptor (c3d) of target cells. Some of these lymphocytes productively infected with EBV undergo lysis and do not survive, but others latently infected become immortalized and acquire the capacity to proliferate. EBV had not been thought to be associated with T cell lymphoma but recently the EBV genomes have been detected in neoplastic T cells, many of which expressed the CD8 p h e n ~ t y p e . ~ ~ We examined the lymph nodes of four patients with IM to determine the phenotypic expression of EBV-infected lymphocytes. Paraffin sections (3pm) were first stained by immunohistochemistry (IHC) using the alkaline phosphatase (ALP)-labeled avidin method employing primary antibodies of L26 (DAKO) as a B cell marker, CD3 (DAKO) as well as UCHL-1 (DAKO) as a T cell marker. They were stained bright red by the ALP reaction with naphthol-AS-BI phosphoric acid as a substrate and hexazotized new fuchsin as a coupler. In situ hybridization (ISH) was then performed using a digoxigenin-labeled oligonucleotide antisense probe for EBVencoded small RNA (EBER-1). The sections were treated with anti-digoxigenin alkaline phosphatase-conjugated antibody and then visualized with 5-bromo-4-chloro-3-indolyl phosphate (BCIP) and nitroblue tetrazorium salt (NTB) to produce purple-black signals. The sense probe and specimens of EBV-negative lymphadenitis were used as controls and gave completely negative results.