Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.4.21.69 (APC)
 16,337 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The CD28 molecule expressed on the surface of T cells plays a pivotal role in transducing costimulatory signals necessary for cell activation. CD28 coligation enhances tyrosine phosphorylation and phosphoinositol 3-kinase association in responsive cells. CD28 cross-linking has also been reported to activate inositol phospholipid turnover and to cause release of intracellular calcium. Here we examine the effects of CD28 cross-linking on early activation of protein kinase C (PKC). We have reported recently that either PMA or CD28 cross-linking synergizes with signals delivered by superantigen and cytokines to induce the proliferation of APC-depleted T cells. Unlike PMA, CD28 cross-linking alone failed to induce an increase in membrane-associated PKC activity. However, PKC activation was seen in resting T cells when CD28 was cross-linked in the presence of superantigen plus APC-derived supernatant, which by themselves had no effect on PKC activity. Inhibition of PKC activity using calphostin C blocked the response of pure T cells to superantigen in the presence of either autologous APC, PMA, or CD28 cross-linking. This effect was specific; it was only seen when calphostin C was added within the first hour of stimulation. Assays of [Ca2+]i levels showed that CD28 cross-linking augmented and prolonged the rise in [Ca2+]i induced in T cells by superantigen and APC-derived cytokines. In the presence of superantigen, the proliferative response of T cells costimulated by CD28 cross-linking was cyclosporin A-sensitive, whereas in the presence of PMA, CD28 cross-linking conferred resistance to cyclosporin A. Both the phosphorylation of phospholipase C gamma 1 at tyrosine and the rise in [Ca2+]i induced by CD28 cross-linking in preactivated T cells were blocked by herbimycin A. Herbimycin A treatment also blocked the ability of CD28 cross-linking to induce a rise in [Ca2+]i in resting T cells. We conclude that CD28 costimulatory signals augment superantigen-induced TCR signals by converging onto common TCR effector pathways involving the activation of phospholipase C gamma 1 and PKC and by generating a cyclosporin A-sensitive pathway.
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PMID:CD28 cross-linking augments TCR-mediated signals and costimulates superantigen responses. 753 90

Cross-linking of specific tumor antigens with the T-cell-associated CD3 and CD28 antigens can increase IL-2 secretion, proliferation and antigen-specific cytotoxicity in resting T cells. This cross-linking can be achieved effectively by bispecific monoclonal antibodies (BiMAb) with specificity for both the tumor antigen and CD3 or CD28 antigen, respectively. To take advantage of the enhanced activation of CD3 pre-activated T cells by additional activation via the CD28 antigen, BiMAb OKT3/HRS-3 with reactivity to both CD3 and the Hodgkin's-lymphoma-associated CD30 antigen and the BiMAb 15E8/HRS-3 with reactivity to both CD28 and CD30 antigen were generated by hybridoma fusion. Resting T cells, represented by Jurkat cells (CD3+/CD28+) were specifically activated to produce IL-2 by co-cultivation with an EBV-transformed B-cell line (LAZ509, CD30+/CD19+) only in the presence of the CD30/CD28 cross-linking BiMAb and an additional cross-linking anti-CD3/CD19 BiMAb (OKT3/6A4). Neither the cross-linking BiMAbs alone nor any combination of the monospecific parental MAbs induced a comparable IL-2 production by Jurkat cells in the presence of LAZ509. In addition, using a combination of these BiMAbs, an antigen-dependent cytotoxicity was induced by targeting APC-depleted peripheral blood lymphocytes to CD30+ L540 cells. T cells, previously specifically activated by CD3/CD30 in the presence of CD30 antigen, were cytotoxic to CD30+ cell lines only after incubation with BiMAb anti-CD28/CD30. Neither of the BiMAbs nor any of the parental antibodies induced a comparable effect. Our results indicate that such BiMAbs may offer a new approach for specific immunotherapy of Hodgkin's lymphoma, which takes advantage of cytokine secretion and cytotoxicity of activated T cells.
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PMID:CD30-antigen-specific targeting and activation of T cells via murine bispecific monoclonal antibodies against CD3 and CD28: potential use for the treatment of Hodgkin's lymphoma. 768 89

Purified CD4+ T cells require TCR engagement and Ag-nonspecific co-stimulatory signals to produce IL-2 and proliferate. A number of recent studies have demonstrated that the interaction of the B7 molecule expressed on APC with the T cell-associated CD28 molecule provides a potent co-stimulatory signal to both freshly isolated CD4+ T cells and cloned Th1 cells. Earlier reports have described the role of cytokines, in particular IL-6 and IL-1, as costimulatory molecules for T cell activation. We previously reported that IL-6 and IL-1 synergize to co-stimulate proliferation of purified mouse CD4+ T cells in conjunction with anti-TCR mAb. In this report we explore the interaction of IL-6, IL-1, and CD28 signaling in the activation of mouse CD4+ T cells, and demonstrate that the co-stimulatory requirements of the cells vary depending on the mode of TCR stimulation. CD28 signaling is not sufficient to co-stimulate responses of high buoyant density CD4+ T cells to anti-TCR-conjugated agarose beads; there is an additional requirement that can be supplied by exogenous IL-6 but not by IL-1. In contrast, in responses to anti-TCR mAb that is passively bound to the bottom of culture wells, CD28 stimulation is sufficient to co-stimulate proliferation, resulting in a very high level of IL-2 production; there is no additional requirement for exogenous IL-6 or IL-1. Possible explanations for the differential requirement for IL-6 in the two systems are discussed. Our results are consistent with the notion that CD28 signaling plays a central role in co-stimulating T cell responses. However, the results also suggest that, depending on the nature of the TCR stimulus, T cell activation may also require additional co-stimulatory signals provided by cytokines.
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PMID:Role of IL-6, IL-1, and CD28 signaling in responses of mouse CD4+ T cells to immobilized anti-TCR monoclonal antibody. 790 3

The costimulatory receptor CD28 is important in the development of both Th1 and Th2 responses. To further assess the requirement for CD28 in the development of Th1 and Th2 responses, we analyzed the ability of T cells from wild-type or CD28- mice to secrete cytokines in MLRs with B lymphomas. We find that in the absence of added IL-12, B lymphomas expressing the alternate costimulatory ligand 4-1BBL can support the production of IL-2 and IL-4 but little detectable IFN-gamma by allogeneic CD28+ and CD28- T cells. IL-4 production by CD28+ or CD28- T cells responding to B7(low) B lymphomas was abrogated by blocking 4-1BB ligand-4-1BB interaction. When APC express high levels of B7 family molecules as well as 4-1BBL, soluble 4-1BB inhibits IL-4 production by CD28- but not by CD28+ cells. Addition of IL-12 to the CD28- MLRs results in increased production of IFN-gamma and decreased amounts of IL-2 and IL-4. Thus, both Th1 and Th2 responses can develop in the complete absence of a signal through the CD28 molecule. CD28+ and CD28- T cells differed, however, with respect to the effect of IL-12 on IL-4 production. IL-12 severely curtailed the amount of IL-4 produced in the CD28- T cell cultures but had a less profound effect on the level of IL-4 produced in the CD28+ cultures, suggesting that a strong signal through the CD28 molecule prevents down-regulation of IL-4 production by IL-12.
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PMID:Role of IL-12 and 4-1BB ligand in cytokine production by CD28+ and CD28- T cells. 912 Feb 60

The Tec family of protein tyrosine kinases plays an important role in T cell signaling. Tec, the prototypical member of this kinase family, can interact with CD28, which is a costimulatory molecule. However, the regulation of Tec upon CD28 stimulation remains poorly understood. Here we show that CD28-B7-mediated interactions are likely involved in the relocalization of Tec at the contact zone between T cells and APC. Upon CD28 ligation with specific antibodies or natural ligands, Tec translocates to the plasma membrane where it colocalizes with the CD28 molecule. The Src-homology 3(SH3) domain of Tec and the two proline-rich motifs of CD28 are involved in this process. Furthermore, we show that CD28 signaling requires the SH3 domain of Tec as well as proline residues present in the intracytoplasmic tail of CD28. These results should provide new insights into the complex regulation of Tec kinases in T cells.
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PMID:The SH3 domain of Tec kinase is essential for its targeting to activated CD28 costimulatory molecule. 1521 45

Full activation of T cells requires the binding of antigen to the T cell receptor and stimulation of the CD28 molecule, a process which typically occurs when T cells bind to an antigen presenting cell. The transcription factor, NF-kappaB, is an integration point for these two signals and its activation is critical for T cell function. Using antibodies to the TCR and CD28 molecules to activate Jurkat T cells, we show that cells that were permitted to aggregate into multi-cellular clusters increased NF-kappaB activity compared to unclustered cells. Inhibition of PI3K signaling with wortmannin decreased the clustering-mediated NF-kappaB signal. Over-expression of a dominant negative form of Cbl-b, an endogenous inhibitor of PI3K, in unclustered cells rescued NF-kappaB activation to the same levels caused by cell clustering. Inhibiting signaling through Rho with dominant negative RhoA abrogated both clustering-mediated and dominant negative Cbl-b-mediated NF-kappaB inactivation, but not TCR/CD28 mediated NF-kappaB activation. Taken together, these results suggest that in addition to pathways stimulated by classical T cell-APC interactions, another signal arising from T cell clustering can enhance activation.
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PMID:T cell-to-T cell clustering enhances NF-kappaB activity by a PI3K signal mediated by Cbl-b and Rho. 1592 96