Early interactions of human herpesvirus 6 with lymphoid cells: Role of membrane protein components and glycosaminoglycans in virus binding

A microassay was developed to detect human herpesvirus 6 (HHV-B) binding to its cellular receptor using flow cytometry. Comparable results were obtain ed either by using HHV-6 preparations conjugated with fluorescein isothiocy anate or by indirect immunofluorescent labeling of membrane-bound virus usi ng as primary antibody a monoclonal antibody specific for the HHV-6 gp60/11 0 envelope glycoprotein. Virus attachment to the plasma membrane was specif ic and saturable. As expected, among cell lines of various origin, maximum binding was detected on human T-lymphoid cells (HSB-2). Papain digestion of HSB-2 cells prevented HHV-B attachment and reduced significantly virus inf ection, indicating the involvement of a protein-based receptor in the attac hment step. After removal of the protease, virus receptors were resynthesiz ed and their regeneration was prevented partially by cycloheximide, an inhi bitor of protein synthesis. Unexpectedly, only high concentrations (mg/ml) of soluble heparan sulfate and heparin inhibited HHV-6 binding and infectio n. Under the same conditions, few micrograms (per ml) of heparin suppressed completely herpes simplex type 1 (HSV-1) attachment to the same cell line. Treatment of HSB-2 cells with heparitinase and heparinase, at doses that r educed significantly HSV-1 attachment, had little effect on HHV-6 binding t o the cell membrane, indicating a different requirement of heparan sulfate- containing glycosaminoglycans for the two herpesviruses. These data suggest that protein components of the cellular membrane play an essential role in HHV-6 binding and infection while heparan sulfate-glycosaminoglycans appea r to be involved only partially in virus-receptor interaction. J. Med. Viro l. 62:487-497, 2000. (C) 2000 Wiley-Liss, Inc.