Observations on the type of infection by Epstein-Barr virus in peripheral lymphoid cells of patients with infectious mononucleosis.

Transformation to continuous cell lines has been studied in cultures of peripheral leuckocytes from infectious mononucleosis (IM) patients and in co-cultures of IM leukocytes and foetal cord blood leukocytes of opposite sex. The transformed cells in the co-cultures were of mixed origin with foetal cells usually predominating. Neutralizing antisera to EB virus markedly reduced or abolished the incidence of transformation in IM leukocyte cultures. This effect was not due to cytotoxicity and followed the pattern seen with cultures where transformation was known to depend on the inter-cellular transfer of infectious EB virus. The findings suggest that EB virus is harboured in peripheral lymphocytes of IM patients as a non-productive unexpressed infection which is activated to produce virus in vitro, the particles released then infecting neighbouring cells to give transformed lines. The differences between this mechanism and the one whereby lines arise in culture from malignant cells of Burkitt's lymphoma are considered, and their significance is discussed.