VIRAL GLYCOPROTEINS ACCUMULATE IN NEWLY FORMED ANNULATE LAMELLAE FOLLOWING INFECTION OF LYMPHOID-CELLS BY HUMAN-HERPESVIRUS-6

Ultrastructural analysis of HSB-2 T-lymphoid cells and human cord bloo d mononuclear cells infected with human herpesvirus 6 revealed the pre sence, in the cell cytoplasm, of annulate lamellae (AL), which were ab sent in uninfected cells. Time course analysis of the appearance of AL following viral infection showed that no AL were visible within the f irst 72 h postinfection and that their formation correlated with the e xpression of the late viral glycoprotein gp116. The requirement of act ive viral replication for AL neoformation was further confirmed by exp eriments using inactivated virus or performed in presence of the viral DNA polymerase inhibitor phosphonoacetic acid, Both conventional elec tron microscopic examination and immunogold fracture labeling with ant i-endoplasmic reticulum antibodies indicated a close relationship of A L with the endoplasmic reticulum and nuclear membranes. However, when the freeze-fractured cells were immunogold labeled with an anti-gp116 monoclonal antibody, AL membranes were densely labeled, whereas nuclea r membranes and endoplasmic reticulum cisternae appeared virtually unl abeled, showing that viral envelope glycoproteins selectively accumula te in AL. In addition, gold labeling with Helix pomatia lectin and whe at germ agglutinin indicated that AL cisternae, similar to cis-Golgi m embranes, contain intermediate, but not terminal, forms of glycoconjug ates. Taken together, these results suggest that in this cell-virus sy stem, AL function as a viral glycoprotein storage compartment and as a putative site of O-glycosylation.