Replication of Epstein-Barr virus: ultrastructural and immunofluorescent studies of P3HR1-superinfected Raji cells

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Abstract
By EM and immunofluorescence, the different steps of the replication of the P3HR1 strain of Epstein-Barr virus in [human Burkitt''s lymphoma] Raji cells were studied. The virus entered the cell by fusion of the viral envelope with the plasma membrane, followed by the disintegration of the capsid. In some cases, the migration of nucleocapsids toward the nuclear membrane was observed. The synthesis of new virions began as early as 7 h after infection (in the case of a high multiplicity of infection [MOI], 800 particles/cell) and took place in low-electron-density areas of the nucleus. A viral envelope was acquired by budding through the nuclear membrane or more often through membranes of the Golgi apparatus or cytoplasmic vacuoles. Comparing immunofluorescence and EM data a good correlation was found between the presence of early antigen and ultrastructurally altered cells, and between the presence of viral capsid antigen and virus-producing cells. With different MOI, different types of viral cycles were observed: at a low MOI (.ltoreq. 50 particles/cell), a nonproducer cycle was induced with early antigen synthesis only; at a higher MOI (100 particles/cell), a transient production of a small amount of virions was observed; and at a high MOI (.gtoreq. 300 particles/cell), a productive cycle was the rule.