Alan B. Rickinson

Methylation of Transcription Factor Binding Sites in the Epstein-Barr Virus Latent Cycle Promoter Wp Coincides with Promoter Down-Regulation during Virus-Induced B-Cell Transformation

ABSTRACT Two Epstein-Barr virus latent cycle promoters for nuclear antigen expression, Wp and Cp, are activated sequentially during virus-induced transformation of B cells to B lymphoblastoid cell lines (LCLs) in vitro. Previously published restriction enzyme studies have indicated hypomethylation of CpG dinucleotides in the Wp and Cp regions of the viral genome in established LCLs, whereas these same regions appeared to be hypermethylated in Burkitts lymphoma cells, where Wp and Cp are inactive. Here, using the more sensitive technique of bisulfite genomic sequencing, we reexamined the situation in established LCLs with the typical pattern of dominant Cp usage; surprisingly, this showed substantial methylation in the 400-bp regulatory region upstream of the Wp start site. This was not an artifact of long-term in vitro passage, since, in cultures of recently infected B cells, we found progressive methylation of Wp (but not Cp) regulatory sequences occurring between 7 and 21 days postinfection, coincident with the period in which dominant nuclear antigen promoter usage switches from Wp to Cp. Furthermore, in the equivalent in vivo situation, i.e., in the circulating B cells of acute infectious mononucleosis patients undergoing primary EBV infection, we again frequently observed selective methylation of Wp but not Cp sequences. An effector role for methylation in Wp silencing was supported by methylation cassette assays of Wp reporter constructs and by bandshift assays, where the binding of two sets of transcription factors important for Wp activation in B cells, BSAP/Pax5 and CREB/ATF proteins, was shown to be blocked by methylation of their binding sites.

Selective accumulation of virus-specific CD8+ T cells with unique homing phenotype within the human bone marrow

The bone marrow plays a unique role within the immune system. We compared the phenotype and function of virus-specific CD8(+) T cells from matched samples of human peripheral blood and bone marrow. Analysis of virus-specific memory CD8(+) T cells showed widely divergent partition of antigen-specific populations between blood and bone marrow. T cells specific for Epstein-Barr virus (EBV) lytic antigens were enriched 3-fold in marrow compared with blood, whereas the response to EBV latent epitopes was equivalent between the 2 compartments. No difference in EBV viral load or expression of the EBV lytic protein was observed between blood and bone marrow. In direct contrast, although cytomegalo-virus (CMV)-specific T cells were the largest virus-specific population within peripheral blood, they were reduced by 60% within marrow. Bone marrow T cells were found to exhibit a unique CCR5(+)CXCR6(+)CXCR3(-) homing phenotype which has not been observed on T cells from other secondary lymphoid organs or peripheral organs. Expression of CCR5 and CXCR6 was higher on EBV-specific T cells within peripheral blood compared with CMV-specific populations. These observations identify a novel bone marrow homing phenotype for CD8(+) memory T cells, which necessitates a reevaluation of the magnitude of antigen-specific populations within the lymphoid system.

Cytotoxic T-Lymphocyte Responses to a Polymorphic Epstein-Barr Virus Epitope Identify Healthy Carriers with Coresident Viral Strains

ABSTRACT Cytotoxic T-lymphocyte (CTL) responses to Epstein-Barr virus (EBV) tend to focus on a few immunodominant viral epitopes; where these epitope sequences are polymorphic between EBV strains, host CTL specificities should reflect the identity of the resident strain. In studying responses in HLA-B27-positive virus carriers, we identified 2 of 15 individuals who had strong CTL memory to the pan-B27 epitope RRIYDLIEL (RRIY) from nuclear antigen EBNA3C but whose endogenous EBV strain, isolated in vitro, encoded a variant sequence RKIYDLIEL (RKIY) which did not form stable complexes with B27 molecules and which was poorly recognized by RRIY-specific CTLs. To check if such individuals were also carrying an epitope-positive strain (either related to or distinct from the in vitro isolate), we screened DNA from freshly isolated peripheral blood mononuclear cells for amplifiable virus sequences across the EBNA3C epitope, across a different region of EBNA3C with type 1-type 2 sequence divergence, and across a polymorphic region of EBNA1. This showed that one of the unexplained RRIY responders carried two distinct type 1 strains, one with an RKIY and one with an RRIY epitope sequence. The other responder carried an RKIY-positive type 1 strain and a type 2 virus whose epitope sequence of RRIFDLIEL was antigenically cross-reactive with RRIY. Of 15 EBV-seropositive donors analyzed by such assays, 12 appeared to be carrying a single virus strain, one was coinfected with distinct type 1 strains, and two were carrying both type 1 and type 2 viruses. This implies that a small but significant percentage of healthy virus carriers harbor multiple, perhaps sequentially acquired, EBV strains.