Notch信号调节外周T细胞的活化、增殖与分化

初始T细胞分化为效应T和记忆T细胞受到多种因素调节.最近在Notch信号途径的研究进展显示它也参于T细胞的活化与分化.大量研究已经表明Notch信号途径可以影响T细胞在中枢免疫器官的发育,现在关于它调节外周T细胞的分化状态也积累不少证据,Notch信号活化之后能够改变CD4+和CD8+T细胞分泌细胞因子的特点.以下着重介绍Notch信号参于调节外周T细胞的活化、增殖和分化的最新资料,尽管不同的研究者所得实验结果有冲突之处,但已经提示Notch信号在T细胞外周发育中的重要意义,特别重要的是抗原递呈细胞(APC)可以通过Notch信号途径调节T细胞的分化.     

Salicylate regulates COX-2 expression through ERK and subsequent NF-kappaB activation in osteoblasts

The expression of cyclooxygenase-2 (COX-2) is a characteristic response to inflammation and can be inhibited with sodium salicylate. TNF-alpha plus IFN-gamma can induce extracellular signal-regulated kinase (ERK), IKK, IkappaB degradation and NF-kappaB activation. The inhibition of the ERK pathway with selective inhibitor, PD098059, blocked cytokine-induced COX-2 expression and PGE2 release. Salicylate treatment inhibited COX-2 expression induced by TNF-alpha/IFN-gamma and regulated the activation of ERK, IKK and IkappaB degradation and subsequent NF-kappaB activation in MC3T3E1 osteoblasts. As well, antioxidant-catalase, N-acetyl-cysteine or reduced glutathione-attenuated COX-2 expression in combined cytokines-treated cells. These antioxidants also inhibited the activation of ERK, IKK and NF-kappaB in MC3T3E1 osteoblasts. In addition, TNF-alpha/IFN-gamma stimulated ROS release in the osteoblasts. However salicylate had no obvious effect on ROS release in DCFDA assay. The results showed that salicylate inhibited the activation of ERK and IKK, IkappaB degradation and NF-kappaB activation independent of ROS release and suggested that salicylate exerts its anti-inflammatory action in part through inhibition of the ERK, IKK, IkappaB, NF-kappaB and resultant COX-2 expression pathway.     

Notch 1 signaling regulates peripheral T cell activation

Notch signaling has been identified as an important regulator of leukocyte differentiation and thymic maturation. Less is known about the role of Notch signaling in regulating mature T cells. We examined the role of Notch 1 in regulating peripheral T cell activity in vitro and in vivo. Coligation of Notch 1 together with TCR and CD28 resulted in a dramatic inhibition of T cell activation, proliferation, and cytokine production. This effect was dependent on presenilin activity and induced the expression of HES-1, suggestive of Notch 1 signaling. Biochemical analysis demonstrated an inhibition of AKT and GSK3beta phosphorylation following Notch 1 engagement while other biochemical signals such as TCR and ERK phosphorylation remained intact. Similar effects were observed in vivo in an adoptive transfer model. Therefore, Notch 1 signaling may play an important role in regulating naive T cell activation and homeostasis.     

Signaling lymphocytic activation molecule (SLAM) regulates T cellular cytotoxicity

Signaling lymphocytic activation molecule (SLAM) is a CD2-related surface receptor expressed by activated T cells and B cells. SLAM is a self ligand and enhances T cellular proliferation and IFN-gamma production. A defective SLAM associated protein (SAP) causes X-linked lymphoproliferative syndrome (XLP), a frequently lethal mononucleosis based on the inability to control EBV. We report that SLAM augments TCR-mediated cytotoxicity. In normal CD4(+) and CD8(+) T cells, SLAM enhanced TCR-mediated cytotoxicity. In CD4(+) and CD8(+) Herpesvirus saimiri (H.saimiri) infected T cells, SLAM engagement alone triggered cytotoxicity. Using H.saimiri-transformed T cells as a model system we found that SLAM-engagement promotes the release of lytic granules and a CD95-independent killing that requires extracellular Ca(2+), cytoskeletal rearrangements, and signaling mediated by mitogen-activated protein kinase kinases MEK1/2. SLAM-enhanced cytotoxicity implies an immunoregulatory function by facilitating the elimination of APC and a role in overcoming infections with pathogens requiring a cytotoxic immune response.     

SAP controls T cell responses to virus and terminal differentiation of TH2 cells

SH2D1A, which encodes signaling lymphocyte activation molecule (SLAM)-associated protein (SAP), is altered in patients with X-linked lymphoproliferative disease (XLP), a primary immunodeficiency. SAP-deficient mice infected with lymphocytic choriomeningitis virus had greatly increased numbers of CD8+ and CD4+ interferon-gamma-producing spleen and liver cells compared to wild-type mice. The immune responses of SAP-deficient mice to infection with Leishmania major together with in vitro studies showed that activated SAP-deficient T cells had an impaired ability to differentiate into T helper 2 cells. The aberrant immune responses in SAP-deficient mice show that SAP controls several distinct key T cell signal transduction pathways, which explains in part the complexity of the XLP phenotypes.     

Two sequential activation modules control the differentiation of protective T helper-1 (Th1) cells

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Antibiotic use during infancy promotes a shift in the T(H)1/T(H)2 balance toward T(H)2-dominant immunity in mice

BACKGROUND: Recent epidemiologic studies indicate that antibiotic use in infancy may be associated with an increased risk of development of atopy; however, its precise mechanism remains to be elucidated. OBJECTIVE: The purpose of this study is to clarify whether one such antibiotic, kanamycin, affects the T(H)1/T(H)2 balance. METHODS: BALB/c mice at 3 and 52 weeks of age were orally administered 600 mg/d kanamycin sulfate for 7 consecutive days. Blood samples were collected on weeks 0, 10, 18, and 26 after the cessation of kanamycin treatment, and the effect of the kanamycin treatment on the T(H)1/T(H)2 balance was evaluated on the basis of both the in vivo antibody levels and the in vitro splenocyte cytokine secretion pattern. RESULTS: The administration of kanamycin increased the serum levels of total IgG1 and IgE while decreasing the serum IgG2a levels. Moreover, when spleen cells were stimulated with immobilized anti-CD3 antibody in vitro, such kanamycin treatment enhanced the in vitro IL-4 secretion while reducing the in vitro IFN-gamma secretion. The basal IL-12 p70 secretion levels of splenic dendritic cells in the kanamycin-treated mice were lower than those in the control mice, although no significant difference was seen in IL-12 p40 levels between either group of mice. CONCLUSION: These results suggested that antibiotic use during infancy may indeed quantitatively disturb, qualitatively disturb, or both the intestinal microflora and thereby prevent postnatal T(H)1 cell maturation, thus resulting in a T(H)2-polarized immune deviation.     

Histamine regulates lymphocyte mitogenic responses through activation of specific H1 and H2 histamine receptors.

In previous studies we have reported that patients with mild atopic eczema have enhanced lymphocyte mitogenesis while those with severe disease have markedly suppressed responses. Similarly, histamine in low concentrations enhanced mitogenesis while higher levels inhibit mitogen stimulated thymidine uptake. In the present study, we investigated the kinetics of this response and the interaction of histamine with its cell-surface receptors on lymphocytes. Histamine (10(-3) M) markedly inhibited [3H]-thymidine incorporation to 27% of control levels when added at the beginning of a 72 h culture period. When added after 24 and 48 h of culture, however, the suppression was much less (62 and 88% of control). Lymphocyte cultures pulsed for 1 h with histamine, washed free of the agent and then cultured with mitogen also showed marked suppression of [3H]-thymidine uptake. The kinetics of the response suggest that histamine acts to inhibit initial processing or recruitment steps in the mitogenic assay. Cimetidine, an H2-receptor blocking agent, prevented the suppressive effect of high levels of histamine while diphenhydramine, an H1 blocker, abolished the enhancement observed with low levels. Pre-incubation of mononuclear cell suspensions, which has been shown to decrease suppressor activity, resulted in a decreased response to added histamine. This change in histamine responsiveness was associated with an alteration in H1:H2 histamine binding as determined with a radiolabelled ligand-binding assay. Histamine suppression of mitogenesis was associated with an increase in cellular cAMP levels while enhancement was accompanied by a small increase in cGMP. These data suggest that lymphocyte function may be regulated, in part, by histamine receptor bearing cells with H1 stimulation having a role in enhancement of mitogenesis and H2 stimulation resulting in normal suppressor activity.     

The kinase mTOR regulates the differentiation of helper T cells through the selective activation of signaling by mTORC1 and mTORC2

The kinase mTOR has emerged as an important regulator of the differentiation of helper T cells. Here we demonstrate that differentiation into the T(H)1 and T(H)17 subsets of helper T cells was selectively regulated by signaling from mTOR complex 1 (mTORC1) that was dependent on the small GTPase Rheb. Rheb-deficient T cells failed to generate T(H)1 and T(H)17 responses in vitro and in vivo and did not induce classical experimental autoimmune encephalomyelitis (EAE). However, they retained their ability to become T(H)2 cells. Alternatively, when mTORC2 signaling was deleted from T cells, they failed to generate T(H)2 cells in vitro and in vivo but preserved their ability to become T(H)1 and T(H)17 cells. Our data identify mechanisms by which two distinct signaling pathways downstream of mTOR regulate helper cell fate in different ways. These findings define a previously unknown paradigm that links T cell differentiation with selective metabolic signaling pathways.     

SHP-2 positively regulates adipogenic differentiation in 3T3-L1 cells

The Src homology domain 2 (SH2)-containing tyrosine phosphatase SHP-2 has been implicated in the regulation of proliferation and differentiation in various cell types. Here, we investigated the ability of SHP-2 to mediate insulin-induced adipogenic differentiation of mouse 3T3-L1 cells. We found that the expression of SHP-2 was increased along with adipogenic differentiation. Overexpression of wild-type SHP-2 in 3T3-L1 cells resulted in enhanced adipocyte differentiation. Furthermore, insulin-stimulated adipogenic differentiation of 3T3-L1 cells was abolished by down-regulating SHP-2 expression using short interfering RNA. These results suggest that SHP-2 is a positive effector in signal transduction pathways necessary for adipocyte differentiation. In SHP-2 knockdown cells, the expression of peroxisome proliferator-activated receptor gamma, a master regulator of adipogenesis, was entirely suppressed even in the late phase of differentiation, whereas the expression level of C/EBPdelta was unchanged. These results highlight a novel role of SHP-2 in the signal transduction pathways regulating adipocyte differentiation.     

c-FLIP(S) reduces activation of caspase and NF-kappaB pathways and decreases T cell survival

Effective stimulation of NF-kappaB in T cells following TCR ligation requires the activity of caspase-8. The active caspase-8 complex includes the paracaspase, MALT1, and Bcl-10, which connect to the NF-kappaB pathway. It has been less clear what regulates the level of caspase-8 activity during T cell activation. A likely candidate is cellular FLIP (c-FLIP), an enzymatically inert caspase-8 homologue. Two alternatively spliced forms of c-FLIP exist, a long form (c-FLIP(L)) and a short-form (c-FLIP(S)). The latter lacks the C-terminal caspase-like domain. c-FLIP(L) can heterodimerize with and activate caspase-8 through an activation loop in the C terminus of c-FLIP(L). Here we show that, in contrast to c-FLIP(L), c-FLIP(S) inhibits activation of caspase-8 in T cells, and consequently reduces recruitment of MALT1 and Bcl-10 to the active caspase complex. This results in reduced activity of NF-kappaB. Consequently, T cells from c-FLIP(S)-transgenic mice undergo more rapid cell death both spontaneously and after activation. The findings suggest that c-FLIP(S) functions to reduce the expansion of T cells during an immune response.     

Memory and flexibility of cytokine gene expression as separable properties of human T(H)1 and T(H)2 lymphocytes

CD4+ T cell priming under T helper type I (T(H)1) or T(H)2 conditions gives rise to polarized cytokine gene expression. We found that in these conditions human naive T cells acquired stable histone hyperacetylation at either the Ifng or Il4 promoter. Effector memory T cells showed polarized cytokine gene acetylation patterns in vivo, whereas central memory T cells had hypoacetylated cytokine genes but acquired polarized acetylation and expression after appropriate stimulation. However, hypoacetylation of the nonexpressed cytokine gene did not lead to irreversible silencing because most T(H)1 and T(H)2 cells acetylated and expressed the alternative gene when stimulated under opposite T(H) conditions. Such cytokine flexibility was absent in a subset of T(H)2 cells that failed to up-regulate T-bet and to express interferon-gamma when stimulated under T(H)1 conditions. Thus, most human CD4+ T cells retain both memory and flexibility of cytokine gene expression.