Yuetsu Tanaka

Microbial Compounds Selectively Induce Th1 Cell-Promoting or Th2 Cell-Promoting Dendritic Cells In Vitro with Diverse Th Cell-Polarizing Signals

Upon microbial infection, specific Th1 or Th2 responses develop depending on the type of microbe. Here, we demonstrate that different microbial compounds polarize the maturation of human myeloid dendritic cells (DCs) into stably committed Th1 cell-promoting (DC1) or Th2 cell-promoting (DC2) effector DCs that polarize Th cells via different mechanisms. Protein extract derived from the helminth Schistosoma mansoni induced the development of DC2s that promote the development of Th2 cells via the enhanced expression of OX40 ligand. Likewise, toxin from the extracellular bacterium Vibrio cholerae induced development of DC2s as well, however, via an OX40 ligand-independent, still unknown mechanism. In contrast, toxin from the intracellular bacterium Bordetella pertussis induced the development of DC1s with enhanced IL-12 production, which promotes a Th1 cell development. Poly(I:C) (dsRNA, mimic for virus) induced the development of extremely potent Th1-inducing DC1, surprisingly, without an enhanced IL-12 production. The obtained DC1s and DC2s are genuine effector cells that stably express Th cell-polarizing factors and are unresponsive to further modulation. The data suggest that the molecular basis of Th1/Th2 polarization via DCs is unexpectedly diverse and is adapted to the nature of the microbial compounds.

Genetic and epigenetic inactivation of tax gene in adult T‐cell leukemia cells

To clarify the status of tax gene, we analyzed human T‐cell leukemia virus type‐I (HTLV‐I) associated cell lines and fresh adult T‐cell leukemia (ATL) cells. We compared 2 types of HTLV‐I associated cell lines: one was derived from leukemic cells (leukemic cell line) and the other from nonleukemic cells (nonleukemic cell line). Although all nonleukemic cell lines expressed Tax, it could not be detected in 3 of 5 leukemic cell lines, in which nonsense mutation or deletion (60 bp) of tax genes, and DNA methylation in 5′‐LTR were identified as the responsible changes. We found such genetic changes of the tax gene in 5 of 47 fresh ATL cases (11%). The tax gene transcripts could be detected in 14 of 41 fresh ATL cases (34%) by RT‐PCR. In ATL cases with genetic changes that could not produce Tax protein, the tax gene was frequently transcribed, suggesting that such cells do not need the transcriptional silencing. Although DNA methylation of 5′‐LTR was detected in the fresh ATL cases (19 of 28 cases; 68%), the complete methylation associated with transcriptional silencing was observed only in 4 cases. Since partial methylation could not silence the transcription, and the tax gene transcription was not detected in 27 of 41 cases (66%), the epigenetic change(s) other than DNA methylation is considered to play an important role in the silencing.

Cross-Talk between Activated Human NK Cells and CD4+ T Cells via OX40-OX40 Ligand Interactions

It is important to understand which molecules are relevant for linking innate and adaptive immune cells. In this study, we show that OX40 ligand is selectively induced on IL-2, IL-12, or IL-15-activated human NK cells following stimulation through NKG2D, the low affinity receptor for IgG (CD16) or killer cell Ig-like receptor 2DS2. CD16-activated NK cells costimulate TCR-induced proliferation, and IFN-γ produced by autologous CD4+ T cells and this process is dependent upon expression of OX40 ligand and B7 by the activated NK cells. These findings suggest a novel and unexpected link between the natural and specific immune responses, providing direct evidence for cross-talk between human CD4+ T cells and NK receptor-activated NK cells.

Fratricide among CD8+ T Lymphocytes Naturally Infected with Human T Cell Lymphotropic Virus Type I

Infection and gene expression by the human T lymphotropic virus type I (HTLV-I) in vivo have been thought to be confined to CD4(+) T lymphocytes. We show here that, in natural HTLV-I infection, a significant proportion of CD8(+) T lymphocytes are infected by HTLV-I. Interestingly, HTLV-I-specific but not Epstein-Barr virus-specific CD8(+) T lymphocytes were shown to be infected. Furthermore, HTLV-I protein expression in naturally infected CD8(+) T lymphocytes renders them susceptible to fratricide mediated by autologous HTLV-I-specific CD8(+) T lymphocytes. Fratricide among virus-specific CTLs could impair the immune control of HTLV-I and possibly other lymphotropic viruses.

Thymic stromal lymphopoietin fosters human breast tumor growth by promoting type 2 inflammation

TSLP released from human breast cancer cells promotes OX40L expression on DCs, and these OX40L-expressing DCs drive development of inflammatory Th2 cells which promote breast tumor development.

A duodenally absorbable CXC chemokine receptor 4 antagonist, KRH-1636, exhibits a potent and selective anti-HIV-1 activity

A low molecular weight nonpeptide compound, KRH-1636, efficiently blocked replication of various T cell line-tropic (X4) HIV type 1 (HIV-1) in MT-4 cells and peripheral blood mononuclear cells through the inhibition of viral entry and membrane fusion via the CXC chemokine receptor (CXCR)4 coreceptor but not via CC chemokine receptor 5. It also inhibited binding of the CXC chemokine, stromal cell-derived factor 1α, to CXCR4 specifically and subsequent signal transduction. KRH-1636 prevented monoclonal antibodies from binding to CXCR4 without down-modulation of the coreceptor. The inhibitory effect against X4 viral replication by KRH-1636 was clearly reproduced in the human peripheral blood lymphocyte/severe combined immunodeficiency mouse system. Furthermore, this compound was absorbed into the blood after intraduodenal administration as judged by anti-HIV-1 activity and liquid chromatography MS in the plasma. Thus, KRH-1636 seems to be a promising agent for the treatment of HIV-1 infection.

Human T-lymphotropic virus, type 1, tax protein triggers microtubule reorientation in the virological synapse

We showed recently that the human T-lymphotropic virus, type 1 (HTLV-1), spreads directly from cell to cell via a virological synapse. The HTLV-1 virological synapse resembles the immunological synapse; each is a specialized contact between a lymphocyte and another cell that contains organized protein microdomains, and each involves repolarization of the T-cell microtubule cytoskeleton. However, formation of the virological synapse is not triggered by T-cell receptor-mediated antigen recognition. On the basis of our previous data, we postulated that formation of the viral synapse was triggered by a conjunction of two signals, one from HTLV-1 infection of the T-cell and one from cell-cell contact. We have recently identified ICAM-1 engagement as a cell-contact signal that causes the microtubule polarization associated with the virological synapse. Here we used confocal microscopy of T-lymphocytes naturally infected with HTLV-1 or transfected with individual HTLV-1 genes to investigate the role of the viral transcriptional transactivator protein Tax. Polarization of the microtubules was induced by cell-cell contact or by cross-linking T-cell surface molecules with monoclonal antibodies adsorbed to latex beads. We show that Tax, which is mainly found in the nucleus, is also present at two specific extranuclear sites as follows: around the microtubule organizing center in association with the cis-Golgi and in the cell-cell contact region. We show that expression of Tax provides an intracellular signal that synergizes with ICAM-1 engagement to cause the T-cell microtubule polarization observed at the virological synapse.

Regulation of Human Immunodeficiency Virus Type 1 Env-Mediated Membrane Fusion by Viral Protease Activity

ABSTRACT We and others have presented evidence for a direct interaction between the matrix (MA) domain of the human immunodeficiency virus type 1 (HIV-1) Gag protein and the cytoplasmic tail of the transmembrane envelope (Env) glycoprotein gp41. In addition, it has been postulated that the MA domain of Gag undergoes a conformational change following Gag processing, and the cytoplasmic tail of gp41 has been shown to modulate Env-mediated membrane fusion activity. Together, these results raise the possibility that the interaction between the gp41 cytoplasmic tail and MA is regulated by protease (PR)-mediated Gag processing, perhaps affecting Env function. To examine whether Gag processing affects Env-mediated fusion, we compared the ability of wild-type (WT) HIV-1 Env and a mutant lacking the gp41 cytoplasmic tail to induce fusion in the context of an active (PR+) or inactive (PR−) viral PR. We observed that PR− virions bearing WT Env displayed defects in cell-cell fusion. Impaired fusion did not appear to be due to differences in the levels of virion-associated Env, in CD4-dependent binding to target cells, or in the formation of the CD4-induced gp41 six-helix bundle. Interestingly, truncation of the gp41 cytoplasmic tail reversed the fusion defect. These results suggest that interactions between unprocessed Gag and the gp41 cytoplasmic tail suppress fusion.

Transcriptional activation of survivin through the NF‐κB pathway by human T‐cell leukemia virus type I tax

Survivin, a unique member of the inhibitor of apoptosis protein family, is overexpressed in many cancers and considered to play an important role in oncogenesis. We previously reported the survivin expression profile in ATL, a CD4‐positive T‐cell malignancy caused by HTLV‐I. HTLV‐I Tax is thought to play an important role in immortalization of T cells. We have shown also that the expression of Tax protected the mouse T‐cell line CTLL‐2 against apoptosis induced by deprivation of IL‐2 and converted its growth from being IL‐2 dependent to being IL‐2 independent through the NF‐κB pathway. In our study, we demonstrate that constitutive expression of survivin was associated with resistance to apoptosis after IL‐2 deprivation in Tax‐expressing CTLL‐2 cells. Transient transfection assays showed that survivin promoter was transactivated by Tax, via the activation of NF‐κB. Pharmacological NF‐κB inhibition resulted in suppression of survivin expression and caused apoptosis of Tax‐expressing CTLL‐2 cells. Our findings suggest that activated NF‐κB signaling contributes directly to malignant progression of ATL by preventing apoptosis, acting through the prosurvival protein survivin.

Inhibitory effects of fucoxanthin, a natural carotenoid, on N-myc expression and cell cycle progression in human malignant tumor cells

Fucoxanthin, a natural carotenoid prepared from brown algae, inhibited the growth of GOTO cells, a human neuroblastoma cell line. Fucoxanthin at 10 micrograms/ml reduced the growth rate of GOTO cells to 38% of the control at day 3 after drug treatment. Flowcytometric analysis revealed that fucoxanthin caused the arrest in the G0-G1 phase of cell cycle. Expression of N-myc gene was proved to be decreased by fucoxanthin as early as 4 h after treatment at 10 micrograms/ml and that may be important for the mechanism of anti-proliferative action of the carotenoid.