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Hidefumi Kojima

Publications and source records attributed to Hidefumi Kojima.

12 recordsLinked to original sources
PubMed2007

TACI regulates IgA production by APRIL in collaboration with HSPG.

Transmembrane activator and calcium modulator and cyclophilin ligand interactor (TACI) is a member of the tumor necrosis factor (TNF) receptor family that serves as a receptor for B-cell activating factor of the TNF family (BAFF) and as a proliferation-inducing ligand (APRIL). Although TACI is reported to function as a positive or negative regulator for B-cell responses, its roles remain elusive. Experiments using TACI siRNA into B cells indicated that TACI positively regulated APRIL-induced IgA production in collaboration with heparan sulfate proteoglycans (HSPG). Furthermore, TACI negatively regulated BAFF-induced B-cell proliferation and production of IgA and IgG. In addition, B cells treated with heparitinase to denature HSPG showed that HSPG is essential for APRIL-induced B-cell responses such as B-cell proliferation, IgG and IgA production, induction of activation-induced cytidine deaminase (AID), and noncanonical NF-kappaB2. In contrast, phosphorylation of physiological AID kinase, protein kinase A (PKA), was dependent on TACI. Importantly, coligation of TACI and HSPG by specific antibodies, but not by TACI or HSPG ligation itself, could induce the phosphorylation of PKA and IgA production instead of APRIL. Our findings indicate that simultaneous binding of TACI and HSPG on B cells with APRIL is crucial for IgA production.

B-Cell Activating Factor↗
PubMed2007

TACI attenuates antibody production costimulated by BAFF-R and CD40.

B cell activating factor of the TNF family (BAFF), plays critical roles in B cell survival, activation, differentiation, and antibody (Ab) production. BAFF binds to three receptors: BAFF-R, transmembrane activator and calcium-modulator and cyclophilin ligand interactor (TACI) and B cell maturation antigen. While BAFF-R is the primary receptor for B cell costimulation by BAFF, TACI is reported to serve as a positive or negative regulator for B cell responses depending on conditions. To determine the real role of TACI in B cell responses, we examined the functional relationship between TACI and BAFF-R in Ab production from human peripheral blood B cells using agonistic mAb. BAFF-R and CD40 enhanced IgG secretion and B cell proliferation, which were inhibited by TACI. Although TACI induced mild B cell apoptosis, its extent did not correlate with that of TACI-mediated inhibition of IgG secretion. In addition, TACI inhibited B-lymphocyte-induced maturation protein-1 expression, IgG secretion from previously IgG-negative selected B cells, and activation-induced cytidine deaminase expression enhanced by BAFF-R and CD40. Importantly, BAFF-R and CD40 enhanced B cell responsiveness to TACI-mediated suppression. Thus, BAFF may attenuate T cell-independent and -dependent B cell responses by TACI.

Adjuvants, Immunologic↗
PubMed2006

Cutting edge: hypoxia-inducible factor 1alpha and its activation-inducible short isoform I.1 negatively regulate functions of CD4+ and CD8+ T lymphocytes.

To evaluate the role of hypoxia-inducible factor 1alpha (HIF-1alpha) and its TCR activation-inducible short isoform I.1 in T cell functions, we genetically engineered unique mice with: 1) knockout of I.1 isoform of HIF-1alpha; 2) T cell-targeted HIF-1alpha knockdown; and 3) chimeric mice with HIF-1alpha gene deletion in T and B lymphocytes. In all three types of mice, the HIF-1alpha-deficient T lymphocytes, which were TCR-activated in vitro, produced more proinflammatory cytokines compared with HIF-1alpha-expressing control T cells. Surprisingly, deletion of the I.1 isoform, which represents < 30% of total HIF-1alpha mRNA in activated T cells, was sufficient to markedly enhance TCR-triggered cytokine secretion. These data suggest that HIF-1alpha not only plays a critical role in oxygen homeostasis but also may serve as a negative regulator of T cells.

Animals↗
PubMed2006

Identification of a glioma antigen, GARC-1, using cytotoxic T lymphocytes induced by HSV cancer vaccine.

Despite several ongoing clinical trials of immunotherapies against glioma, few glioma-specific antigens recognized by cytotoxic T lymphocytes (CTLs) have been identified. We recently demonstrated that intratumoral inoculation with herpes simplex virus (HSV) as a cancer vaccine activates tumor-specific CTLs. To identify glioma antigens recognized by CTLs, we used the HSV cancer vaccine to vaccinate mice harboring a syngeneic mouse glioma cell line, GL261. From the splenocytes of the immunized mice, we generated an H-2Db-restricted CTL line, GCL-1, that was specific for GL261. Then, a cDNA expression library generated from GL261 was screened with GCL-1, and a new gene encoding glioma antigen, GARC-1, was isolated. Sequence analysis revealed that the GARC-1 gene isolated from GL261 had a point mutation causing an amino acid change (Asp to Asn at position 81). T-cell epitope analysis revealed that the mutated peptide GARC-1(77-85) (AALLNKLYA) but not the wild-type peptide (AALLDKLYA), was recognized by GCL-1. These results suggest that HSV cancer vaccination may be a useful method for inducing tumor-specific CTLs and identifying tumor antigens. Furthermore, this GL261/GARC-1 murine glioma model may be useful for the development of immunotherapy for brain tumors.

Animals↗
PubMed2005

CD4+CD25+ regulatory T cells attenuate the phosphatidylinositol 3-kinase/Akt pathway in antigen-primed immature CD8+ CTLs during functional maturation.

This study was designed to determine the role of CD25(+)CD4(+) regulatory T (Tr) cells in CTL maturation and effector functions using a murine CTL line and in vitro MLC. Tr cells inhibited CTL functional maturation, but had no effect on CTL effector functions. In CD4(+) responder T cell-depleted MLC supplemented with IL-2, Tr cells suppressed mature CTL generation only when added within the first 2 days of culture. Tr cells down-regulated levels of active Akt, but not STAT5 or ZAP70 in Ag-primed immature CTLs. Down-regulation of active Akt was accompanied by a reduction in CTL cell size and IL-2Ralpha expression. In Tr cell-depleted MLC, CTLs were generated that exhibited high levels of nonspecific cytotoxicity. Our in vitro findings suggest that Tr cells regulate functional CTL maturation to generate optimal Ag-specific immune responses through the control of the PI3K/Akt pathway.

Animals↗
PubMed2004

Essential role of OX40L on B cells in persistent alloantibody production following repeated alloimmunizations.

OX40/OX40 ligand (OX40L) interactions are implicated in costimulation for both CD4(+) T and B cells in a bidirectional manner. To determine the role of OX40/OX40L interactions in recipient antidonor responses after multiple allogeneic transfusions, we examined alloreactive cytotoxic T lymphocyte (allo-CTL) activity and alloantibody production in repeatedly alloimmunized OX40L-deficient mice. After the fifth alloimmunization, whereas OX40L-deficient mice showed allo-CTL activity with levels comparable to those of wild-type mice, alloantibody production in OX40L-deficient mice was significantly reduced, accompanied by fewer memory B and CD4(+) T cells with reduced function. Furthermore, nu/nu mice that received OX40L-deficient T cells still exhibited impaired alloantibody production with fewer memory CD4(+) T and B cells. In contrast, RAG-2-deficient mice that received both wild-type T cells and OX40L-deficient B cells produced scant alloantibodies with fewer memory B cells, but sufficient memory CD4(+) T cells. Thus, OX40L on B cells, rather than on T cells, is apparently required for adequate and persistent production of alloantibodies after repeated alloimmunizations.

Animals↗
PubMed2004

Physiological control of immune response and inflammatory tissue damage by hypoxia-inducible factors and adenosine A2A receptors.

Immune cell-mediated destruction of pathogens may result in excessive collateral damage to normal tissues, and the failure to control activated immune cells may cause immunopathologies. The search for physiological mechanisms that downregulate activated immune cells has revealed a critical role for extracellular adenosine and for immunosuppressive A2A adenosine receptors in protecting tissue from inflammatory damage. Tissue damage-associated deep hypoxia, hypoxia-inducible factors, and hypoxia-induced accumulation of adenosine may represent one of the most fundamental and immediate tissue-protecting mechanisms, with adenosine A2A receptors triggering "OFF" signals in activated immune cells. In these regulatory mechanisms, oxygen deprivation and extracellular adenosine accumulation serve as "reporters," while A2A adenosine receptors serve as "sensors" of excessive tissue damage. The A2A receptor-triggered generation of intracellular cAMP then inhibits activated immune cells in a delayed negative feedback manner to prevent additional tissue damage. Targeting A2A adenosine receptors may have important clinical applications.

Adenosine↗
PubMed2003

BAFF/BLyS can potentiate B-cell selection with the B-cell coreceptor complex.

The tumor necrosis factor (TNF)-like ligand BAFF/BLyS (B-cell activating factor of the TNF family/B-lymphocyte stimulator) is a potent B-cell survival factor, yet its functional relationship with other B-cell surface molecules such as CD19 and CD40 is poorly understood. We found that follicular dendritic cells (FDCs) in human lymph nodes expressed BAFF abundantly. BAFF up-regulated a B cell-specific transcription factor Pax5/BSAP (Pax5/B cell-specific activator protein) activity and its target CD19, a major component of the B-cell coreceptor complex, and synergistically enhanced CD19 phosphorylation by B-cell antigen receptor (BCR). BAFF further enhanced B-cell proliferation, immunoglobulin G (IgG) production, and reactivity to CD154 by BCR/CD19 coligation and interleukin-15 (IL-15). Our results suggest that BAFF may play an important role in FDC-B-cell interactions through the B-cell coreceptor complex and a possibly sequential link between the T cell-independent and -dependent B-cell responses in the germinal centers.

Antibodies, Monoclonal↗
PubMed2003

HIF-1 alpha deficiency perturbs T and B cell functions.

The immune system protects organisms from pathogens. The immune cells, in particular T- and B-lymphocytes, develop and acquire effector functions in specialized tissues called the lymphoid organs. The lymphoid organs exhibit lower oxygen tensions than the blood or the atmosphere. Furthermore, inflammatory and tumor environments where lymphocytes execute effector functions also have very low oxygen tensions. These findings led to the hypothesis that lymphocytes may have evolved adaptive mechanisms to function under hypoxic conditions. Cellular responses to hypoxia are triggered by the hypoxia inducible factor-1 alpha (HIF-1 alpha). In this paper we review the development and function of T- and B-lymphocytes in the absence HIF-1 alpha. Our studies suggest that HIF-1 alpha deficiency depresses the function of cytotoxic T-lymphocytes and blocks B-cell development in the bone marrow. B1 lymphocytes of fetal origin, on the other hand, accumulate and may produce auto-antibodies and autoimmunity.

Animals↗
PubMed2002

CD27 and CD40 inhibit p53-independent mitochondrial pathways in apoptosis of B cells induced by B cell receptor ligation.

B cells in the germinal center are known to undergo apoptosis after B cell receptor (BCR) ligation, a process relevant to immunological tolerance. Human CD27 is a B cell co-stimulatory molecule. The aim of this study was to compare the effects of CD27 and CD40 signals on BCR-mediated apoptosis of B cells. BCR ligation activated mitochondrial apoptotic pathways including down-regulation of Bcl-X(L), dissipation of mitochondrial transmembrane potential, release of cytochrome c, and activation of caspase-9. Each of these effects was significantly inhibited by CD27 and CD40. Bik expression was weakly but significantly down-regulated by CD27 but up-regulated by CD40. BCR ligation resulted in p53 activation including its phosphorylation at Ser(15), nuclear translocation, and target gene p53AIP1 induction. CD27 and CD40 clearly suppressed these processes. Analyses that used dominant-negative p53 variants revealed a low but still substantial level of BCR-mediated apoptosis and intact mitochondria-mediated apoptotic pathway. These pathways were further inhibited by CD27 and CD40, although the cells showed no p53 phosphorylation or p53AIP1 expression. Our results suggested that, at the mitochondrial level, CD27 and CD40 co-stimulatory signals regulated the p53-amplified apoptotic pathway in B cells through the inhibition of p53-independent apoptotic pathway primarily induced by BCR ligation.

Apoptosis↗
PubMed2002

Abnormal B lymphocyte development and autoimmunity in hypoxia-inducible factor 1alpha -deficient chimeric mice.

Immune cells are exposed to low oxygen tensions as they develop and migrate between blood and different tissues, but the mechanisms by which lymphocytes adapt to hypoxia are poorly understood. Studies reported here of hypoxia-inducible factor 1alpha (HIF-1alpha) in lymphocyte development and functions suggest that it has a critical role in regulation of these processes. HIF-1alpha deficiency in Hif1alpha(-/-) --> Rag2(-/-) chimeric mice results in dramatic and cell lineage-specific defects, which include appearance of abnormal peritoneal B-1-like lymphocytes, with high expression of B220 (CD45) receptor-associated protein tyrosine phosphatase and autoimmunity (accumulation of anti-dsDNA antibodies and rheumatoid factor in serum, deposits of IgG and IgM in kidney and proteinuria) as well as distortions of maturation of B-2 lymphocytes in bone marrow.

Animals↗