Epstein-Barr virus (EBV) invasion of B-lymphocytes involves Epstein-Barr virus (EBV)2 invades B-lymphocytes through molecular interactions involving the EBV gp350/220 protein. It is known that gp350 binds to B-lymphocyte CR2 (known as C3d receptor) with a 3.2 nM affinity constant (12 nM affinity has been determined for B-lymphocyte surface) (1, 2). This simple 1:1 interaction is involved in adsorption, capping, and EBV endocytosis and is considered to be a primary determinant of EBV tissue tropism (3-5). The CR2 region binding to gp350 overlaps the CR2 region binding to C3dg. The gp350 N-terminal region contains part of the B-lymphocyte binding domain (5).The gp350 21 EDPGFFNVE 29 peptide, having significant homology with C3d-amino acid sequences (6), binds to purified CR2 and to CR2(ϩ) but not to CR2(Ϫ) B-and T-lymphoblastoid cell lines; this peptide coupled to BSA inhibits CR2 binding to EBV and gp350 (7). This peptide inhibits C3dg binding to B-cells (as well as EBV) and also inhibits C3-induced Raji cell proliferative response (7,8).However, the 470-mer N-terminal recombinant protein and gp220, containing this peptide sequence, present single-component binding, whereas gp350/220 presents a higher affinity two-component binding to CR2 (5, 9) and inhibits only 50% of EBV binding and EBV infection of Raji cells (5) (5). On the other hand, the C3dg region (homologous to this gp350 peptide) is not in contact with CR2 in the reported complex structure (10). It is thus very likely that other gp350/220 regions are involved in EBV binding to B-lymphocytes.The gp350/220 region containing the epitope recognized by neutralizing monoclonal antibody 72A1 is one of the most important regions involved in gp350/220 binding to B-lymphocyte CR2, because the mAb 72A1 Fab fragment inhibits EBV binding and invasion of host cells (5, 11). Moreover, mAb 72A1 inhibits EBV invasion of monocytes (12), neutrophils (13), and T-cells (14). Anti-gp350/220 mAb 72A1 also inhibits interleukin-6 (IL-6) protein synthesis induced in PBLs by gp350/220 binding to CR2 (15); it also inhibits EBV invasion of B-lymphocytes (5). It is known that the gp350/220 region involved in EBV invasion of host cells is recognized by this monoclonal antibody; however, its precise localization remains unknown. The purpose of this work was thus to identify B-lymphocyte binding sequences that are involved in EBV virus infection of B-lymphocytes. MATERIALS AND METHODSPeptide Synthesis-Forty-six peptides, covering the total length of EBV gp350-reported sequence (16), were synthesized by the solid phase method (17) with N-terminal t-Boc-protected amino acids. Peptides were cleaved by a low-high hydrogen fluoride protocol (18). These peptides were analyzed by mass spectrometry and reverse-phase high performance liquid chromatography. Synthesized peptide sequences are shown in Fig. 1. Tyrosine (Y) was C-terminally added, allowing those peptides not containing this amino acid to be radiolabeled.Lymphoblastoid Cell Line Cultures-The cloned Raji (19), Ramos (20), and P3HR-1 ...

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