Epstein–Barr virus (EBV) is the etiologic agent of infectious mononucleosis and African Burkitt’s lymphoma. Its complete nucleotide sequence of 172 kbp is smaller than other herpes viruses but has been thoroughly mapped. Although EBV is morphologically simi-lar to the other herpesviruses, it can be cultured easily only in lymphoblastoid cell lines derived from B lymphocytes of humans and higher primates. In vivo, EBV is tropic for both human B lymphocytes and epithelial cells. The former is a nonproductive infection, while the latter is productive. The virus generally does not produce cytopathic effects or the characteristic intranuclear inclusions of other herpesvirus infections. After infection with EBV, lymphoblastoid cells containing viral genome can be cultivated continuously in vitro; they are thus transformed, or immortalized. Recent studies suggest that most of the viral DNA in transformed cells remains in a circular, nonintegrated form as an epi-some, while a lesser amount is integrated into the host cell genome. Viral antigen ex-pression has been studied by immunofluorescent staining of transformed cell lines under various conditions. One group of proteins, called EBV nuclear antigens (EBNAs), ap-pear in the nucleus prior to virus-directed protein synthesis. Viral capsid antigen (VCA) can be detected in cell lines that produce mature virions. Other cell lines, called nonpro-ducers, contain no mature virions, but express certain virus-associated antigens called early antigens (EAs). The latter may be seen as diffuse (D) and as restricted (R) aggre-gates of staining.
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