Epstein-Barr virus (EBV) induces human B cell

No abstract

Summary. Cord blood T cells are much more likely to be induced to apoptosis in vitro than adult T cells. Nevertheless, the expression of Fas is markedly lower on cord blood lymphocytes than on peripheral blood lymphocytes. In the current investigation, we determined the capacity of tumour necrosis factor-a (TNF-a) to induce apoptosis in human naõ Ève T cells in cord blood, and assessed the roles of two distinct TNF receptors (TNFRs) in mediating death signals. After activation, cord blood T cells were sensitive to TNF-ainduced apoptosis, and interleukin 2 (IL-2) could prevent this apoptotic response. Both TNFR1 (p55) and TNFR2 (p75) expressed on activated cord blood T cells were able to transmit apoptotic signals. Moreover, a synergistic effect was observed by a combination of TNFR1-and TNFR2-signals. Additionally, CD41 T cells showed higher sensitivity to TNFR-mediated apoptosis than CD8 1 T cells. These data suggest that TNF-a probably is a mediator of apoptosis in cord blood T cells in vivo and may contribute to the low incidence of graft-versus-host disease in cord blood transplantation.

A cDNA library was constructed from poly(A) + RNA isolated from the iododeoxyuridine-treated P3HR1 cell line. Five cDNA clones, which hybridized with the BamHI G fragment of Epstein-Barr virus (EBV) DNA, were subcloned and sequenced. Clones G2, G3 and G4 corresponded to the BGLF2 open reading frame (ORF) of EBV (B95-8, nucleotides 126837 to 125 866); G3 was found to contain the entire BGLF2 ORF. The predicted M, of the putative protein product of the EBV B95-8 BGLF20RF is 36K. Complete nucleotide sequencing of G3 revealed that there were two nucleotide changes from the reported sequence of the EBV B95-8 BGLF2 gene, but these did not alter the predicted amino acid sequence of the products. Clone G3 and a cDNA derived from it by N-terminal deletion were expressed in Escherichia coli, producing fusion proteins. Rabbit antisera against these proteins were shown to react with viral capsid antigen-expressing HR1 cells in an indirect immunofluorescence assay. In vitro transcription/translation products and fusion proteins expressed in E. coli were used to determine the presence of antibodies in sera from EBV-infected individuals. The results of immunoprecipitation and immunoblotting studies showed that the majority of EBV-seropositive individuals mount a serum antibody response to the BGLF20RF-encoded protein.

Induction of apoptosis of virus-infected cells is an important host cell defense mechanism. It is well documented that T cells may undergo apoptosis due to interactions between Fas and Fas ligand (FasL). In addition, signals that induce apoptosis in T cells can result from interaction of tumor necrosis factor (TNF)-alpha with TNF receptors (TNFRs). It has been shown that human T cell lines expressing HTLV-I have decreased sensitivity to Fas-mediated apoptosis. The susceptibility of HTLV-I-infected cells to TNF-alpha-induced apoptosis remains to be elucidated. In the present study, we examined the expression of TNFRs on HTLV-I-infected T cell lines that expressed T-cell activation markers and thus phenotypically resemble activated T cells. Different from primary activated T cells that expressed both TNFRs, none of the five HTLV-I-infected T cell lines studied had detectable TNFR1 and only three had TNFR2 on their cell surfaces, although, the RNA transcripts of both TNFR genes could be detected via reverse transcription-polymerase chain reaction in these cell lines. The T cell blasts, which we activated in vitro, were sensitive to apoptosis induced by TNF-alpha and by antibodies to TNFR1 and/or TNFR2. However, all of the HTLV-I-infected cell lines expressing TNFR2 were resistant to TNF-alpha-mediated apoptosis. These findings suggest that HTLV-I infection may interfere with the autonomous suicide programs of T cells, not only Fas/FasL but also TNFRs/TNF-alpha pathways, to prolong the life of the infected cells. This may contribute to viral persistence and favor survival and subsequent expansion of dysregulated infected T cells with the potential to produce HTLV-I-associated autoimmune-like diseases or malignancies.