Biomedical subjects

Manabu Fujimoto

Publications and source records attributed to Manabu Fujimoto.

9 recordsLinked to original sources

PubMed2003

CD19 regulates innate immunity by the toll-like receptor RP105 signaling in B lymphocytes.

Lipopolysaccharide (LPS) is a major gram-negative bacterial component that stimulates innate immune response and also induces B-lymphocyte activation. Recent studies have revealed that common molecular patterns of microorganisms such as LPS are recognized by toll-like receptors (TLRs). B cells have 2 known TLRs that mediate LPS signaling, TLR4 and RP105 (CD180). While TLR4 is expressed on immune cells of various types, RP105 is preferentially expressed on mature B cells. Here we demonstrate that CD19 plays a major role in regulating signal transduction through RP105. Anti-RP105 ligation induced normal proliferation of B cells from mice deficient for MyD88, an adaptor protein that mediates most TLR pathways. By contrast, the loss of CD19 resulted in modest B-cell proliferation against anti-RP105 stimulation as well as LPS stimulation. LPS induced tyrosine phosphorylation of CD19, which was RP105-dependent but TLR4-independent. CD19 formed a complex with Lyn and Vav following RP105 ligation, and CD19 expression was required for optimal Lyn activation and Vav phosphorylation. Consistently, B cells deficient for CD19 exhibited specific defect in the activation of c-Jun N-terminal kinases following RP105 ligation and LPS stimulation. In contrast, CD19 and phosphatidylinositol 3-kinase independently regulated intracellular calcium mobilization induced by anti-RP105 stimulation. Thus, signaling through the B-cell-specific LPS receptor RP105 is uniquely regulated by the B-cell-specific signaling component, Lyn/CD19/Vav complex.

Animals↗

PubMed2003

Interleukin 15 induces the signals of epidermal proliferation through ERK and PI 3-kinase in a human epidermal keratinocyte cell line, HaCaT.

Interleukin 15 (IL-15) is a potent stimulator of proliferation and an inhibitor of apoptosis in lymphocytes. We attempted to elucidate the mechanism of IL-15 function in HaCaT keratinocytes. We found that 5-bromo-2(')-deoxyuridine incorporation increased in a dose-dependent manner with IL-15. This was blocked by MEK inhibitor U0126 or PI 3-K inhibitor LY294002. ERK1/2 and Akt phosphorylation by IL-15 were detected in a dose- and time-dependent manner. U0126 and LY294002 abolished ERK1/2 and Akt phosphorylation, respectively. DNA fragmentation and Annexin V binding accompanied by UVB-induced apoptosis were reduced by 30-50% with IL-15. Taken together, IL-15 induced cellular proliferation and had an anti-apoptotic effect on keratinocytes, in which ERK1/2 and Akt phosphorylation played crucial roles. The signal transduction pathways of IL-15 in keratinocytes were partially elucidated; they share a substantial part with growth signals induced by EGF. These results suggest a therapeutic approach to inflammatory skin diseases by controlling these signals.

Apoptosis↗

PubMed2003

Function blocking autoantibodies against matrix metalloproteinase-1 in patients with systemic sclerosis.

Systemic sclerosis is characterized by fibrosis and systemic autoimmunity; however, roles of autoantibodies in the development of fibrosis remain unknown in systemic sclerosis. The net accumulation of extracellular matrix is dependent on the balance between the synthesis and degradation of extracellular matrix components, the latter process regulated by matrix metalloproteinases. Matrix metalloproteinase-1 (interstitial collagenase-1) can initiate degradation of collagen types I-III that are major extracellular matrix constituents in affected skin of systemic sclerosis. In this study, we tested the hypothesis that systemic autoimmunity in systemic sclerosis induced anti-matrix metalloproteinase-1 autoantibodies that inhibited matrix metallo-proteinase-1 activity, resulting in collagen accumulation. Enzyme-linked immunosorbent assay using human recombinant matrix metalloproteinase-1 revealed that IgG anti-matrix metalloproteinase-1 autoantibody levels were significantly elevated in sera from patients with systemic sclerosis, but not patients with active systemic lupus erythematosus or dermatomyositis, relative to normal controls. IgG anti-matrix metalloproteinase-1 autoantibody levels were significantly higher in patients with diffuse cutaneous systemic sclerosis than those found in patients with limited cutaneous systemic sclerosis. Furthermore, IgG anti-matrix metalloproteinase-1 antibody levels significantly correlated with the extent of fibrosis in the skin, lung, and renal blood vessels. The presence of IgG anti-matrix metalloproteinase-1 autoantibody in sera from systemic sclerosis patients was confirmed by immunoblotting analysis. Remarkably, IgG anti-matrix metalloproteinase-1 autoantibody in sera from systemic sclerosis patients inhibited matrix metalloproteinase-1 collagenase activity. Collectively, the results of this study suggest that anti-matrix metalloproteinase-1 autoantibody contributes to the development of fibrosis by inhibiting matrix metalloproteinase-1 collagenase activity and reducing the extracellular matrix turnover and suggest that the presence of anti-matrix metalloproteinase-1 autoantibody in systemic sclerosis is the link between systemic autoimmunity and fibrosis.

Adult↗

PubMed2003

Serum levels of tumor necrosis factor and interleukin-13 are elevated in patients with localized scleroderma.

BACKGROUND: The enhanced production of some cytokines may be related to the pathogenesis of localized scleroderma (LSc). OBJECTIVE: To determine whether serum levels of tumor necrosis factor (TNF) and interleukin (IL)-13 are elevated, and whether they correlated with clinical or serological features in patients with LSc. METHODS: Serum levels of TNF and IL-13 were examined by ELISA in 45 patients with LSc and in 20 healthy controls. RESULTS: The frequency of serum TNF detection was significantly higher in patients with LSc (24%) compared with that in healthy controls (0%). The frequency of serum IL-13 detection was also significantly higher in patients with LSc (29%) compared with that in controls (0%). In patients with LSc, elevated TNF levels significantly correlated with the presence of IgM antihistone antibodies, anti-single-stranded DNA antibodies, elevated serum IL-6 levels, the number of linear lesions, and muscle involvement. Elevated IL-13 levels were significantly associated with the number of plaque lesions and the total number of lesions. CONCLUSIONS: These results suggest that TNF and IL-13 may be associated with the development of LSc.

Adolescent↗

PubMed2003

Serum concentrations of the CXC chemokines interleukin 8 and growth-regulated oncogene-alpha are elevated in patients with systemic sclerosis.

OBJECTIVE: To determine whether serum concentrations of 2 CXC chemokines, interleukin 8 (IL-8) and growth-regulated oncogene-alpha (GRO-alpha), which are potent chemoattractants and activators for neutrophils, are elevated and whether they correlate with clinical features in patients with systemic sclerosis (SSc). METHODS: Serum samples from patients with diffuse cutaneous SSc (dSSc; n = 36), limited cutaneous SSc (lSSc; n = 42), systemic lupus erythematosus (SLE; n = 15), dermatomyositis (DM; n = 15), and healthy controls (n = 35) were examined by ELISA. RESULTS: Serum IL-8 was detected significantly more frequently in patients with dSSc (61%) and lSSc (55%) relative to healthy controls (6%), patients with SLE (7%), and those with DM (13%). Similarly, serum GRO-alpha concentrations in SSc patients were significantly increased compared with controls, patients with SLE, or those with DM. Elevated IL-8 concentrations significantly correlated with decreased % DLCO and rheumatoid factor positivity, while increased GRO-alpha levels were significantly associated with decreased % DLCO and % vital capacity, involvement of kidney and muscle, the presence of anti-topoisomerase I antibody, and increased serum IgG levels. CONCLUSION: Our results suggest that the elevation of serum levels of the CXC chemokines IL-8 and GRO-alpha is specific to SSc and that the elevation of CXC chemokines, particularly GRO-alpha, correlates with the involvement of internal organs, especially pulmonary damage.

Adolescent↗

PubMed2002

Complementary roles for CD19 and Bruton's tyrosine kinase in B lymphocyte signal transduction.

CD19 and Bruton's tyrosine kinase (Btk) may function along common signaling pathways in regulating intrinsic and B cell Ag receptor (BCR)-induced signals. To identify physical and functional interactions between CD19 and Btk, a CD19-negative variant of the A20 B cell line was isolated, and CD19-deficient (CD19(-/-)) and CD19-overexpressing mice with the X-linked immunodeficient (Xid; Btk) mutation were generated. In A20 cells, Btk physically associated with CD19 following BCR engagement. CD19 and Btk interactions were not required for initial Btk phosphorylation, but CD19 expression maintained Btk in an activated state following BCR engagement. In primary B cells, CD19 signaling also required downstream Btk function since CD19-induced intracellular Ca(2+) ([Ca(2+)](i)) responses were modest in Xid B cells. In addition, CD19 overexpression did not normalize the Xid phenotype and most phenotypic and functional hallmarks of CD19 overexpression were not evident in these mice. However, CD19 and Btk also regulate independent signaling pathways since their combined loss had additive inhibitory effects on BCR-induced [Ca(2+)](i) responses and CD19 deficiency induced a severe immunodeficiency in Xid mice. Thus, CD19 expression amplifies or prolongs Btk-mediated signaling, rather than serving as a required agent for Btk activation. Consistent with this, phosphatidylinositol 3-monophosphate kinase and Akt activation were normal in CD19(-/-) B cells following IgM engagement, although their kinetics of activation was altered. Thus, these biochemical and compound gene dosage studies indicate that Btk activation and [Ca(2+)](i) responses following BCR engagement are regulated through multiple pathways, including a CD19/Src family kinase-dependent pathway that promotes the longevity of Btk signaling.

Agammaglobulinaemia Tyrosine Kinase↗

PubMed2002

CD83 expression influences CD4+ T cell development in the thymus.

T lymphocyte selection and lineage commitment in the thymus requires multiple signals. Herein, CD4+ T cell generation required engagement of CD83, a surface molecule expressed by thymic epithelial and dendritic cells. CD83-deficient (CD83-/-) mice had a specific block in CD4+ single-positive thymocyte development without increased CD4+CD8+ double- or CD8+ single-positive thymocytes. This resulted in a selective 75%-90% reduction in peripheral CD4+ T cells, predominantly within the naive subset. Wild-type thymocytes and bone marrow stem cells failed to differentiate into mature CD4+ T cells when transferred into CD83-/- mice, while CD83-/- thymocytes and stem cells developed normally in wild-type mice. Thereby, CD83 expression represents an additional regulatory component for CD4+ T cell development in the thymus.

Adoptive Transfer↗

PubMed2002

CD19-dependent B lymphocyte signaling thresholds influence skin fibrosis and autoimmunity in the tight-skin mouse.

The tight-skin (TSK/+) mouse, a genetic model for human systemic sclerosis (SSc), develops cutaneous fibrosis and autoantibodies against SSc-specific target autoantigens. Although molecular mechanisms explaining the development of fibrosis and autoimmunity in SSc patients or TSK/+ mice remain unknown, we recently demonstrated that SSc patients overexpress CD19, an important regulatory molecule expressed by B lymphocytes. B cells from CD19-deficient mice are hyporesponsive to transmembrane signals, while B cells overexpressing CD19 are hyperresponsive and generate autoantibodies. In this study, TSK/+ B cells also exhibited a hyperresponsive phenotype with decreased surface IgM expression, enhanced serum Ig production, and spontaneous autoantibody production. Moreover, CD19 tyrosine phosphorylation was constitutively augmented in TSK/+ B cells. CD19-mediated [Ca(2+)](i) responses, Vav phosphorylation, and Lyn kinase activity were similarly enhanced. Studies of TSK/+ mice deficient in CD19 expression demonstrated that CD19 deficiency significantly decreased skin fibrosis in TSK/+ mice. Additionally, CD19 loss in TSK/+ mice upregulated surface IgM expression and completely abrogated hyper-gamma-globulinemia and autoantibody production. CD19 deficiency also inhibited IL-6 production by TSK/+ B cells. Thus, chronic B cell activation resulting from augmented CD19 signaling in TSK/+ mice leads to skin sclerosis possibly through IL-6 overproduction as well as autoimmunity.

ADP-ribosyl Cyclase↗

PubMed2002

Effects of endoscopic transthoracic sympathicotomy on hemodynamic and neurohumoral responses to exercise in humans.

Endoscopic transthoracic sympathicotomy (ETS) is a minimal invasive procedure of thoracic sympathetic block and has been used successfully in the treatment of primary palmar hyperhidrosis. To examine the effect of Th 2-3 ETS on hemodynamic responses to submaximal upright treadmill exercise in humans, cardiac output, plasma noradrenaline and adrenaline at rest and during the last 40s of stage 2 in a modified Bruce protocol were measured before and after ETS in 21 patients with primary palmar hyperhidrosis. Heart rate, mean arterial pressure, rate-pressure product, and noradrenaline decreased at rest and at submaximal exercise after ETS. Cardiac index at rest did not change either before or after ETS, but decreased (8.9 +/- 0.6 vs 6.8 +/- 0.4L x min(-1) m-2; p<0.01, mean +/- SEM) at submaximal exercise after ETS. Stroke index and systemic vascular resistance were similar both at rest and at submaximal exercise before and after ETS. Thus, ETS reduces myocardial oxygen demand and plasma noradrenaline levels both at rest and during exercise without significantly depressing cardiac function in terms of stroke volume.

Adult↗