PDF《Antigen》

1 (EBNA1),3 -2, -3A, -3B, -3C, and -LP and the latent membrane proteins

1 and 2, all of which being expressed in EBV-transformed B-lymphoblastoid cell lines (LCL). In contrast to the latent infection, during which only a limited number of proteins are expressed, activation of the EBV lytic cycle leads to the expression of as many as

80 virus-speci?c RNA species (1). Based on their time of appearance after induc- tion, these transcripts are named immediate-early, early, or late. An intact immune system is capable of containing EBV infection and preventing transformation of infected B cells. In fact, the high frequency of EBV-associated lymphoproliferative diseases or lym- phomas in immunocompromised individuals strongly supports a role for anti-EBV T cells in containing EBV infection (5). The CD8? T cell response, which has been extensively studied, has been shown to be preferentially directed toward the early lytic proteins BZLF1 and BMLF1 (6C11) and, to a lesser extent, toward the latent nuclear Ags EBNA3A, -3B, and -3C (see Ref.

12 for a review). EBV-speci?c CD4? T cell responses have been explored only recently. These studies are of particular interest considering that EBV infects mainly B cells, in which the HLA class II pathway of Ag presentation is active. Upon recognition of EBV-infected B cells, EBV-speci?c CD4? T cells might play a dual role not only in sustaining proliferation and functional maturation of CD8? T cells, but also in directly contributing to elimination of EBV-in- fected B cells. The EBV-speci?c CD4? T cell responses described to date are mainly directed against the EBNA proteins expressed during latency (13C20). Very few CD4? T cell responses to EBV proteins produced during the lytic cycle have been characterized (21C25). We re- cently described a CD4? T cell response directed against an epitope from the early EBV lytic protein BHRF1, presented in the HLA-DR*0401 context (25). We generated a large number of BHRF1-speci?c CD4? T cell clones from several DR*0401? in- dividuals and showed that in all instances these T cell clones dis- played strong killing of DR*0401-matched LCLs. In this study we explored the mechanism that could explain why the percentage of killed LCL cells far exceeded the small percentage of B cells en- tering the lytic cycle. Materials and Methods CD4? T cell lines and T cell clones CD4? T cell lines and CD4? T cell clones were derived from PBL from healthy virus carriers or from synovial ?uid from patients suffering from Institut National de la Sante ? et de la Recherche Me ?dicale, Unite ? 601, Institut de Biologie, Nantes, France Received for publication July 13, 2005. Accepted for publication September 22, 2005. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with

18 U.S.C. Section

1734 solely to indicate this fact.

1 This work was supported by grants from the Ligue Nationale Contre le Cancer, Centre Hospitalier Universitaire de Nantes, European Community (Grant QLK2-CT- 2001-01205), and institutional grants from Institut National de la Sante ? et de la Re- cherche Me ?dicale.

2 Address correspondence and reprint requests to Dr. Elisabeth Houssaint, Institut National de la Sante ? et de la Recherche Me ?dicale, Unite ? 601, Institut de Biologie,

9 quai Moncousu,

44093 Nantes Cedex 01, France. E-mail address: [email protected]

3 Abbreviations used in this paper: EBNA, EBV-encoded nuclear Ag;

BFA, brefeldin A;

CMA, concanamycin A;