Biomedical subjects

Manabu Fujimoto

Publications and source records attributed to Manabu Fujimoto.

At least 37 records · Page 2Linked to original sources

PubMed2004

Dermatitis due to epiregulin deficiency and a critical role of epiregulin in immune-related responses of keratinocyte and macrophage.

Epidermal growth factor (EGF) family members, including epiregulin (EP), play a fundamental role in epithelial tissues; however, their roles in immune responses and the physiological role of EP remain to be elucidated. The skin has a versatile system of immune surveillance. Biologically active IL-1alpha is released to extracellular space upon damage from keratinocytes and is a major player in skin inflammation. Here, we show that EP is expressed not only in keratinocytes but also in tissue-resident macrophages, and that EP-deficient (EP(-/-)) mice develop chronic dermatitis. Wound healing in the skin in EP(-/-) mice was not impaired in vivo, nor was the growth rate of keratinocytes from EP(-/-) mice different from that of WT mice in vitro. Of interest is that in WT keratinocytes, both IL-1alpha and the secreted form of EP induced down-regulation of IL-18 mRNA expression, which overexpression in the epidermis was reported to induce skin inflammation in mice, whereas the down-regulation of IL-18 induced by IL-1alpha was impaired in EP(-/-) keratinocytes. Although bone marrow transfer experiments indicated that EP deficiency in non-bone-marrow-derived cells is essential for the development of dermatitis, production of proinflammatory cytokines by EP(-/-) macrophages in response to Toll-like receptor agonists was much lower, compared with WT macrophages, whose dysfunction in EP(-/-) macrophages was not compensated by the addition of the secreted form of EP. These findings, taken together, suggested that EP plays a critical role in immune/inflammatory-related responses of keratinocytes and macrophages at the barrier from the outside milieu and that the secreted and membrane-bound forms of EP have distinct functions.

Animals↗

PubMed2004

Characterization of multipotent adult stem cells from the skin: transforming growth factor-beta (TGF-beta) facilitates cell growth.

Recently, adult stem cells have been isolated from the skin and designated as skin-derived precursors (SKPs). These SKPs, cultured in vitro, can give rise to neurons, glia, smooth muscle cells, and adipocytes. In the current study, we confirmed the clonal expansion of SKPs using a sphere-forming culture system in a medium containing methylcellulose. Among the growth factors, only transforming growth factor-beta (TGF-beta) was revealed to uniquely facilitate the sphere formation and proliferation of the SKPs in combination with EGF and bFGF. In addition, TGF-beta did not alter phenotypical characteristics of the SKPs under sphere-forming conditions. The effect of TGF-beta on sphere formation was not observed in neural stem cells, which expressed a different set of cell surface markers from SKPs, suggesting that SKPs have distinct features. Although the number of SKPs decreased with age, TGF-beta increased the sphere colony formation and proliferation in all ages. These results suggest that SKPs maintained in the presence of TGF-beta during culture are of potential use in cell-replacement therapies employing adult tissue sources.

Adipocytes↗

PubMed2004

Severely impaired B lymphocyte proliferation, survival, and induction of the c-Myc:Cullin 1 ubiquitin ligase pathway resulting from CD22 deficiency on the C57BL/6 genetic background.

Understanding the molecular mechanisms through which CD22 regulates B lymphocyte homeostasis, signal transduction, and tolerance is critical to defining normal B cell function and understanding the role of CD22 in autoimmunity. Therefore, CD22 function was examined in vivo and in vitro using B cells from CD22-deficient (CD22(-/-)) mice. Backcrossing of founder CD22(-/-) mice onto the C57BL/6 (B6) genetic background from a B6/129 mixed background resulted in a dramatically reduced B cell proliferative response following IgM ligation, characterized by a paucity of lymphoblasts and augmented apoptosis. Also, the phenotype of splenic B6 CD22(-/-) B cells was uniquely HSA(high) and IgD(low)/CD21(low) with intermediate levels of CD5 expression, although the percentages of mature and transitional B cells were normal. That B6 CD22(-/-) B cells predominantly underwent apoptosis following IgM ligation correlated with this unique tolerant phenotype, as well as defective induction of the c-Myc:Cullin 1 (CUL1) ubiquitin ligase pathway that is necessary for progression to the S phase of cell cycle. CD40 ligation compensated for CD22 deficiency by restoring lymphoblast development, proliferation, c-Myc and CUL1 expression, and protein ubiquitination/degradation in IgM-stimulated B6 CD22(-/-) B cell cultures. Thereby, this study expands our current understanding of the complex role of CD22 during B cell homeostasis and Ag responsiveness, and reveals that the impact of CD22 deficiency is dictated by the genetic background on which it is rendered. Moreover, this study defines CD22 and CD40 as the first examples of lymphocyte coreceptors that influence induction of the c-Myc:CUL1 ubiquitin ligase pathway.

Adjuvants, Immunologic↗

PubMed2004

Altered blood B lymphocyte homeostasis in systemic sclerosis: expanded naive B cells and diminished but activated memory B cells.

OBJECTIVE: To determine phenotypic and functional abnormalities of blood B cell subsets in patients with systemic sclerosis (SSc). METHODS: Cell surface marker expression was determined by flow cytometry. Spontaneous apoptosis was evaluated by annexin V expression with flow cytometric analysis. IgG production by isolated IgD- memory B cells was examined by enzyme-linked immunosorbent assay. RESULTS: The numbers of blood CD27- naive B cells from SSc patients were increased compared with normal control cells, while memory B cells expressing medium levels of CD27 and plasmablasts expressing high levels of CD27 were reduced. In contrast, plasmablasts were the predominant population in patients with systemic lupus erythematosus (SLE). Memory B cells in SSc showed increased expression of activation markers, including CD80, CD86, and CD95, relative to normal controls. Consistent with CD95 up-regulation, SSc memory B cells exhibited augmented spontaneous apoptosis after 24-hour incubation; augmented apoptosis may explain the reduced memory B cell number. Nonetheless, isolated IgD- SSc memory B cells treated with stimuli had an enhanced ability to produce IgG. Furthermore, expression of CD19, a critical signal transduction molecule of B cells that regulates autoantibody production, was significantly increased in memory B cells as well as in naive B cells in SSc. In contrast, CD19 expression was decreased in SLE B cells. CONCLUSION: SSc patients have distinct abnormalities of blood homeostasis and B cell compartments, characterized by expanded naive B cells and activated but diminished memory B cells. Our results suggest that CD19 overexpression in SSc memory B cells is related to their hyperreactivity.

Adult↗

PubMed2004

Association of a functional CD19 polymorphism with susceptibility to systemic sclerosis.

OBJECTIVE: CD19 is overexpressed in B cells from patients with systemic sclerosis (SSc), and plays a crucial role not only for autoantibody production, but also for skin fibrosis in mouse models. We previously reported the association of a GT repeat polymorphism in the 3'-untranslated region (3'-UTR) of CD19 with human systemic lupus erythematosus. In this study, we examined whether CD19 polymorphisms are associated with genetic susceptibility to SSc. METHODS: A case-control association study was performed for CD19 polymorphisms, -499G>T in the promoter region and a GT repeat polymorphism in the 3'-UTR, in 134 patients with SSc and 96 healthy individuals recruited at Kanazawa University. CD19 expression levels in the peripheral blood naive and memory B cells from SSc patients were examined by 2-color flow cytometry. RESULTS: Carrier frequencies of the -499T allele in the promoter (odds ratio [OR] 2.18, 95% confidence interval [95% CI] 1.31-3.86, P = 0.003) and of the (GT)(14) allele in the 3'-UTR (OR 1.86, 95% CI 1.05-3.28, P = 0.03) were significantly increased in SSc patients compared with healthy controls. Association was particularly evident in patients with limited cutaneous SSc with anticentromere antibodies. These alleles were in linkage disequilibrium, but the -499T allele seemed to play a primary role. CD19 expression levels in peripheral blood B cells were significantly elevated in both naive (P = 0.0029) and memory (P = 0.0022) B cells from patients with SSc who had the -499T allele as compared with those without the -499T allele. CONCLUSION: The CD19 -499G>T polymorphism is associated with higher CD19 expression in B cells, and with susceptibility to SSc.

Adult↗

PubMed2004

Altered B lymphocyte function induces systemic autoimmunity in systemic sclerosis.

Systemic sclerosis (SSc) is a connective tissue disease characterized by excessive extracellular matrix deposition in the skin and visceral organs. SSc is associated with immune activation characterized by autoantibody production, lymphocyte activation, and release of various cytokines. The presence of autoantibodies is a central feature of immune activation in SSc. Although autoantibodies are thought to be closely linked to the pathogenesis of SSc, the pathogenic relationship between systemic autoimmunity and the clinical manifestations of SSc, including skin fibrosis, remains unknown. Recent studies have revealed that B cells play a critical role in systemic autoimmunity and disease expression through various functions, including cytokine production in addition to autoantibody production. The B cell signaling thresholds are regulated by response regulators that augment or diminish B cell signals during responses to self and foreign antigens. Abnormal regulation of the response regulator function and expression may result in autoantibody production. Among these response regulators, CD19, which is a critical cell-surface signal transduction molecule of B cells, is the most potent positive regulator. Transgenic mice that overexpress CD19 by approximately 3-fold lose tolerance and generate autoantibodies spontaneously. B cells from SSc patients exhibit a 20%-increase in CD19 expression that induces SSc-specific autoantibody production in transgenic mice. Furthermore, SSc patients have intrinsic B cell abnormalities characterized by expanded naive B cells, activated but diminished memory B cells, and chronic hyper-reactivity of memory B cells, possibly due to CD19 overexpression. Similarly, B cells from a tight-skin mouse, a model of SSc, show augmented CD19 signaling and chronic hyper-reactivity. Remarkably, CD19 loss results in inhibition of chronic B cell hyper-reactivity and elimination of autoantibody production, which is associated with improvement in skin fibrosis and a parallel decrease in IL-6 production by B cells. Thus, chronic B cell activation resulting from augmented CD19 signaling leads to skin fibrosis possibly through IL-6 overproduction, as well as autoantibody production, in tight-skin mice and SSc patients.

Animals↗

PubMed2004

B Lymphocyte signaling established by the CD19/CD22 loop regulates autoimmunity in the tight-skin mouse.

Systemic sclerosis (SSc) is characterized by fibrosis and autoimmmunity. Peripheral blood B cells from SSc patients specifically overexpress CD19, a critical cell-surface signal transduction molecule in B cells. CD19 deficiency in B cells also attenuates skin fibrosis in the tight-skin (TSK/+) mouse, a genetic model for SSc. Herein we analyzed two transgenic mouse lines that overexpress CD19. Remarkably, 20% increase of CD19 expression in mice spontaneously induced SSc-specific anti-DNA topoisomerase I (topo I) antibody (Ab) production, which was further augmented by 200% overexpression. In TSK/+ mice overexpressing CD19, skin thickness did not increase, although anti-topo I Ab levels were significantly augmented, indicating that abnormal CD19 signaling influences autoimmunity in TSK/+ mice and also that anti-topo I Ab does not have a pathogenic role. The molecular mechanisms for abnormal CD19 signaling were further assessed. B-cell antigen receptor crosslinking induced exaggerated calcium responses and augmented activation of extracellular signal-regulated kinase in TSK/+ B cells. CD22 function was specifically impaired in TSK/+ B cells. Consistently, CD19, a major target of CD22-negative regulation, was hyperphosphorylated in TSK/+ B cells. These findings indicate that reduced inhibitory signal provided by CD22 results in abnormal activation of signaling pathways including CD19 in TSK/+ mice and also suggest that this disrupted B cell signaling contribute to specific autoantibody production.

Animals↗

PubMed2004

Mechanical stretching in vitro regulates signal transduction pathways and cellular proliferation in human epidermal keratinocytes.

Epidermal keratinocytes are continuously exposed to mechanical forces. The human skin surface can be thickened and enlarged by various stresses such as tissue expander or abrasive pressure. To investigate the mechanism of epidermal hyperproliferation by mechanical stress, keratinocytes were plated on flexible silicone dishes, which were continuously stretched by +20%. Stretching of cells for 24 h caused upregulation of 5-bromo-2'-deoxyuridine (BrdU)-positive cells to 200%-220% and activation of extracellular signal-regulated kinases (ERK)1/2. Inhibition of mitogen and ERK with U0126 and phosphoinositide 3-OH kinase attenuated BrdU incorporation and ERK1/2 activation. The EGF receptor kinase inhibitor and the calcium channel inhibitor also inhibited BrdU incorporation and the activation of ERK1/2. Twenty-four hours of stretching stimulated reporter activity driven by activator protein 1 (AP-1), induction of K6, and suppression of K10, which were inhibited by U0126. Our results indicate that mechanical stretching induces proliferative signals on human keratinocytes via induction of calcium influx, phosphorylation of epidermal growth factor receptor (EGFR), and ERK1/2. These mechanisms may contribute to the hyperproliferative nature of the epidermis, which is mechanically stretched by various stimuli.

Bromodeoxyuridine↗

PubMed2004

[A female case of hyper-IgM immunodeficiency syndrome with uncommon skin manifestations].

A 11-year-old female admitted to our hospital because of erythema of the face and the trunk, and a wide and dense cluster of verruca vulgaris on the right sole. She had no family history of immunodeficiency, no perinatal abnormality, no growth abnormality, or no history of severe infections. From the age of 4 years, she noticed erythema around her nose. At the age of 9 years, small erythema and papules appeared on her chest. In January, 2003, erythema around her nose and papules of the trunk spread rapidly, and she also felt fatigue and effort dyspnea. Laboratory examinations revealed near absence of serum IgG, and IgE, high serum IgM (525 mg/dl), and normal IgA and IgD. Thl/Th2 ratio was 36.9. We diagnosed her as having hyper-IgM syndrome. Histological examinations of a skin biopsy showed the infiltration composed of mainly histiocytes,and mildly atypical CD8 + T cells around the blood vessels in the dermis. We concluded her skin manifestations as reactive lymphohistiocytic infiltration at the base of immunodeficiency and durable stimulation of various antigens. Her skin manifestations improved transiently by the intravenous immunogrobulin and corticosteroids therapy.

Child↗

PubMed2004

Elevated circulating CD40L concentrations in patients with systemic sclerosis.

OBJECTIVE: B cell activation, fibrosis, and expression of adhesion molecules on endothelial cells are regulated by soluble CD40L (sCD40L)/CD40 interactions. Since these effects are characteristic in patients with systemic sclerosis (SSc), serum concentrations of sCD40L were determined in patients with SSc. METHODS: Fifty-two Japanese patients with SSc were examined. They were grouped into 24 patients with limited cutaneous SSc (lSSc) and 28 with diffuse cutaneous SSc (dSSc). Serum sCD40L levels were examined by ELISA. As a disease control, serum samples from 20 patients with systemic lupus erythematosus (SLE) were also examined. In addition, a retrospective longitudinal study was performed in 71 serum samples from 18 patients with SSc. RESULTS: Serum sCD40L levels were elevated in SSc patients compared with healthy controls (p < 0.001). Levels of sCD40L in patients with SSc were higher than in patients with SLE (p < 0.001) that had elevated sCD40L levels compared with healthy controls. Among SSc subsets, there were no differences in sCD40L levels between lSSc and dSSc. sCD40L levels correlated positively with C-reactive protein levels in SSc patients (p < 0.0001, r = 0.449). In a cross-sectional study and a longitudinal study, serum sCD40L levels in dSSc patients were persistently elevated, although those in lSSc patients were temporarily elevated at the early phase of the disease process. CONCLUSION: Patients with SSc exhibited elevated sCD40L levels that may correlate with disease activity. These results suggest that CD40/CD40L interactions may be potential therapeutic targets in SSc.

Adolescent↗

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

Relation between hemodynamic changes after endoscopic transthoracic sympathicotomy and the number of sympathetic segments operated.

We examined the relation between hemodynamic changes after endoscopic transthoracic sympathicotomy (ETS) and the number of sympathetic segment operated. Cardiac functional indices using echocardiography and plasma noradrenaline concentration (NOR) were measured before and after ETS in 25 patients with palmar hyperhidrosis. Patients were divided into 2 groups. Group Th2-3 consisted of 16 patients (mean age 28 +/- 8 years),who underwent Th2-3 ETS. Group Th2-4 consisted of 6 patients (mean age 29 +/- 9 years), who underwent Th2-4 ETS. Before ETS, all hemodynamic parameters and NOR were similar between the 2 groups. After ETS, heart rate, systolic, diastolic, and mean blood pressures, rate-pressure product, and NOR decreased,whereas left ventricular end-systolic volume index, cardiac index, and ejection fraction did not change in the 2 groups. Systemic vascular resistance decreased in group Th2-4, whereas it did not change in group Th2-3. Left ventricular end-diastolic volume index and stroke index increased in group Th2-3, whereas it did not change in group Th2-4. After ETS, rate-pressure product, systolic, diastolic, and mean blood pressures in group Th2-4 were smaller than those in group Th2-3, whereas other parameters were similar between the 2 groups. Among percent changes in all hemodynamic parameters and NOR occurring after ETS, only the percent decrease in systolic blood pressure in group Th2-4 was larger than that in group Th2-3 (-15 +/- 12 % vs.-4+/-8%, respectively, p < 0.05). These findings suggest that only the change in blood pressure is related to the difference in the number of sympathetic segment operated.

Adult↗

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↗