Human Herpesvirus 6 Envelope Glycoproteins B and H-L Complex Are Undetectable on the Plasma Membrane of Infected Lymphocytes

Membrane immunofluorescence analysis of cells infected with either variant (A or B) of human herpesvirus 6 revealed a typical punctate staining, after labeling with several HHV-6-positive human sera or with two monoclonal antibodies directed to gB and gH. Immunoprecipitation studies showed a sharp difference in glycoprotein content in whole-cell extracts versus on the cell surface, suggesting the occurrence of gB in the extracellular virions juxtaposed to plasma membranes. By immunoelectron microscopy, the extracellular virions still attached to the cell surface appeared consistently and specifically labeled, whereas the plasma membrane was always unlabeled, independent of viral variant, antibody, or target cell used. These findings may reflect an atypical maturation pathway of HHV-6, and could have important implications in the control of cellular immune response to HHV-6-infected lymphocytes.