THE EXTRACELLULAR DOMAIN OF THE EPSTEIN-BARR-VIRUS BZLF2 PROTEIN BINDS THE HLA-DR BETA-CHAIN AND INHIBITS ANTIGEN PRESENTATION

The Epstein-Barr virus BZLF2 gene encodes a glycoprotein that associat es with gH and gL and facilitates the infection of B lymphocytes. In o rder to determine whether the BZLF2 protein recognizes a B-cell-specif ic surface antigen, a soluble protein containing the extracellular por tion of the BZLF2 protein linked to the Fc portion of human immunoglob ulin G1 (BZLF2.Fc) was expressed from mammalian cells. BZLF2.Fe was us ed in an expression cloning system and found to bind to a beta-chain a llele of the HLA-DR locus of the class II major histocompatibility com plex (MHC). Analysis of amino- and carboxy-terminal deletion mutants o f the BZLF2.Fc protein indicated that the first 90 amino acids of BZLF 2.Fc are not required for HLA-DR beta-chain recognition. Site-directed mutagenesis of an HLA-DR beta-chain cDNA and subsequent immunoprecipi tation of expressed mutant beta-chain proteins using BZLF2.Fc indicate d that the beta 1 domain, which participates in the formation of pepti de binding pockets, is required for BZLF2.Fc recognition. The addition of BZLF2.Fc to sensitized peripheral blood mononuclear cells in vitro abolished their proliferative response to antigen and inhibited cytok ine-dependent cytotoxic T-cell generation in mixed lymphocyte cultures . Flow-cytometric analysis of Akata cells induced to express late Epst ein-Barr virus antigens indicated that expression of BZLF2 did not res ult in reduced surface expression levels of MHC class II. The ability of BZLF2.Fe to bind to the HLA-DR beta chain suggests that the BZLF2 p rotein may interact with MHC class II on the surfaces of B cells.