Epstein-Barr Virus gH Is Essential for Penetration of B Cells but Also Plays a Role in Attachment of Virus to Epithelial Cells

Abstract

Entry of Epstein-Barr virus (EBV) into B cells is initiated by attachment of glycoprotein gp350 to the complement receptor type 2 (CR2).A complex of three glycoproteins, gH, gL, and gp42, is subsequently required for penetration. Gp42 binds to HLA class II, which functions as an entry mediator or coreceptor and, by analogy with other herpesviruses, gH is then thought to be involved virus-cell fusion. However, entry of virus into epithelial cells is thought to be different. It can be initiated by attachment by an unknown glycoprotein in the absence of CR2. There is no interaction between gp42 and HLA class II and instead a distinct complex of only the two glycoproteins gH and gL interacts with a novel entry mediator. Again, by analogy with other viruses gH is thought to be critical to fusion. To investigate further the different roles of gH in infection of the two cell types and to examine its influence on the assembly of the gH-gL-gp42 complex, we constructed two viruses, one in which the gH open reading frame was interrupted by a cassette expressing a neomycin resistance gene and the gene for green fluorescent protein and one as a control in which the neighboring nonessential thymidine kinase gene was interrupted with the same cassette. Virus lacking gH exited from cells normally, although loss of gH resulted in rapid turnover of gL and gp42 as well. The virus bound normally to B lymphocytes but could not infect them unless cells and bound virus were treated with polyethylene glycol to induce fusion. In contrast, virus that lacked the gH complex was impaired in attachment to epithelial cells and the effects of monoclonal antibodies to gH implied that this resulted from loss of gH rather than other members of the complex. These results suggest a role for gH in both attachment and penetration into epithelial cells.The Epstein-Barr virus (EBV) gH-gL complex consists of three glycoproteins, gp85, the gH homolog which is the product of the BXLF2 open reading frame (ORF) (12, 26); gp25, the gL homolog which is the product of the BKRF2 ORF (38); and gp42, which is the product of the BZLF2 ORF (17). The complex behaves in many respects like its counterparts in other herpesviruses. Glycoprotein gH is dependent on gL for authentic processing and transport (38), and the complex as a whole has been implicated as important to the ability of virus to fuse with the cell membrane and penetrate into the cytoplasm (11,22). The precise roles of the individual members of the complex are, however, still being elucidated and appear to depend in part on the cell type that the virus is infecting.Infection of the B lymphocyte is dependent on an interaction between gp42 and HLA class II (32) which functions as an entry mediator for this cell type (16). A monoclonal antibody (MAb) to gp42 that blocks binding to HLA class II blocks virus-cell fusion (22), B cells that lack class II cannot be superinfected unless class II expression is restored (16), and a virus that lacks gp42 is unable to infect B cells unless a soluble form of gp42 that...

Measuring Epstein–Barr virus (EBV) load: the significance and application for each EBV‐associated disease

“…EBV replicates in a permissive cell type in the oropharynx, probably specialised epithelial cells, that either binds virus directly or acquires virus by transfer from the surface of adjacent B cells (Figure 1) [12]. EBV infects epithelial cells through a CD21-independent mechanism, and the viral glycoprotein gH mediates EBV attachment to CD21-negative epithelial cells [13]. Accumulating evidence suggests that EBV also infects T and NK cells during primary infection.…”

Use of gHgL for Attachment of Epstein-Barr Virus to Epithelial Cells Compromises Infection

“…B-cell virus (B-EBV) was collected from clarified culture medium of EBV-carrying Akata cells after induction of the lytic cycle with antihuman immunoglobulin (Ig) (20). Epithelial cell virus (E-EBV) was harvested from AGS cells after induction with 12-O-tetradecanoylphorbol-13-acetate (Sigma) and 2.5 mM sodium butyrate (Calbiochem, La Jolla, Calif.).…”

“…supplemented with 10% heat-inactivated fetal bovine serum (Gibco/ BRL, Grand Island, N.Y.). Medium for Akata cells carrying EBV in which the thymidine kinase gene was interrupted with a double cassette expressing neomycin resistance and the green fluorescence protein (GFP) (EBV-TKdel) (20) was supplemented with 500-g/ml active G418 (Mediatech, Herndon, Va.). AGS, a CR2-negative gastric carcinoma-derived cell line (American Type Culture Collection), was grown in Ham's F-12 nutrient mixture (Gibco/BRL) supplemented with 10% heat-inactivated fetal bovine serum.…”

“…However, binding to epithelial lines lacking CR2, such as the gastric carcinoma cell line AGS, is dependent on gHgL. gHgL null virus failed to bind to AGS cells (20,25), and a MAb to gHgL that blocked entry into but not binding to an epithelial cell engineered to express CR2 (15) also inhibited this gHgL-dependent virus binding, suggesting, although not definitively proving, that the epithelial coreceptor was also used for attachment on a cell lacking CR2 (20).…”

“…Entry requires fusion of virus with the B-cell membrane, which is mediated by glycoprotein gB (8), and a noncovalently linked complex of three glycoproteins, gH, gL, and gp42 (9,20,37). Glycoprotein gL serves as a chaperone for gH (40), and a recombinant virus with gH deleted also lacks gL (20).…”