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Query: UMLS:C0033036 (APC)
 10,214 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We have examined the responses of cloned T cell lines and of normal T cells to staphylococcal enterotoxins A, B, and C1 (SEA, SEB, and SEC1). SEA, SEB, and SEC1 are all very potent mitogens for T cells in the presence of Ia+ APC. The minimal activating dose of all these SE varies from 1 to 100 ng/ml. As determined by mAb blocking of the responses of both normal T cells and cloned T cell lines, SEA required either the I-A or the I-E molecule on APC for stimulating T cells, whereas SEB required the I-E molecule predominantly over I-A molecule. The TCR:CD4 complex is also involved in the response to SE. The responses to SEB and SEC1 were inhibited by anti-V beta 8 antibody F23.1, whereas the response to SEA and to PHA was not affected by this antibody. Anti-CD4 effectively inhibited responses to all SE but not to PHA. The involvement of the TCR was also confirmed by flow microfluorimetry analysis of T cell blasts responding to SE and the responses of a panel of cloned T cell lines, both of which showed that V beta 8+ T cells preferentially responded to SEB, whereas V beta 8+ T cells failed to respond to SEA. By using fixed APC, it could be shown that processing is not required for the presentation of SE. Furthermore, pulsing experiments showed that SEB can bind to relevant sites on either B cells or T cells, whereas with conventional Ag only prepulsing of the APC has worked. In one case, SEB activates a cloned T cell line in the absence of APC, and this same clone also responds directly to anti-V beta 8 antibody. Thus, SEB appears to bring together V beta 8-expressing TCR with the I-E molecule, whereas SEA apparently has the same effect on TCR expressing different V beta with either the I-A or the I-E molecule, probably depending upon which TCR is bound. The close resemblance between T cell responses to SE and those to mixed-lymphocyte stimulating (Mls) locus suggests to us that a novel SE-like protein that binds both to class II MHC molecules on the APC surface and to V beta gene products on TCR could be the product of the Mls locus.
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PMID:Bacterial proteins that mediate the association of a defined subset of T cell receptor:CD4 complexes with class II MHC. 213 3

Stimulation of T cells by superantigens has been reported to be dependent on the presence of APC where binding to class II molecules is a prerequisite to recognition by the TCR. We examined the response of human T cells and a leukemic T cell line, Jurkat to the superantigen, streptococcal M protein. We show that immobilized or cross-linked streptococcal M protein stimulates Jurkat cells (V beta 8), but not normal purified human T cells, to produce IL-2. Activation of purified T cells by this superantigen required costimulatory signals provided by PMA, IL-1, and IL-6. These cytokines and growth factors alone can induce IL-2 production by T cells; however, proliferation occurred only in the presence of superantigen, which together with PMA, IL-1, and IL-6 induced the expression of IL-2R alpha on T cells. Similar results were obtained when the response of purified T cells to another known superantigen, staphylococcal enterotoxin B were examined, indicating that this phenomenon is not unique to M protein. Superantigens interact with a large number of T cells with particular V beta, and thus provide excellent models for studies of the role of biochemical events and signal transduction in T cell activation. Understanding these events may also explain the pathogenesis of autoimmune diseases associated with certain superantigens, such as streptococcal M protein that is thought to be involved in rheumatic fever and rheumatic heart disease.
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PMID:Accessory cell-independent stimulation of human T cells by streptococcal M protein superantigen. 214 16

The glycosylation inhibiting factor (GIF) was detected in EGTA extracts of the OVA-specific Ts cell hybridoma, 231F1 cells and 71B4 cells, which constitutively secrete GIF. The lymphokine in both culture supernatants and EGTA extracts failed to bind to OVA-Sepharose. Association of GIF with the plasma membrane was confirmed by surface labeling of the 231F1 cells with 125I. The major species of GIF in the extract was 14.4-kDa peptide as determined by SDS-PAGE, and was identical to that detected in culture supernatants. Pretreatment of the cells with monoclonal anti-GIF switched the cells from the formation of unglycosylated IgE-BF to the formation of glycosylated IgE-BF, indicating that the membrane-associated GIF is involved in the determination of the nature of IgE-binding factor during their biosynthesis. When the hybridoma was stimulated with OVA-pulsed APC, EGTA extracts of the cells contained GIF having affinity for OVA. The binding of the OVA-binding GIF in the EGTA extracts to OVA-Sepharose was inhibited by a synthetic peptide, which corresponds to amino acid residues 307-317 in the OVA molecule and represents the epitope recognized by TCR on the cells. The OVA-binding GIF in the extracts bound to the monoclonal anti-TCR-alpha chain, H-28-710 and the mAb 14-12, which is specific for the Ag-binding chain of effector type suppressor factor, and suppressed the in vivo antibody response of BDF1 mice to DNP-OVA in a carrier-specific manner. Evidence was obtained that indicated that the Ag-binding chain was associated with nonspecific GIF chain on the cell surface of the Ag-stimulated cells.
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PMID:Association of glycosylation-inhibiting factor with plasma membranes of T suppressor cell hybridomas. 214 96

The participation of the host in eliminating Ag-specific T hybridoma cells after their in vivo activation was studied. In our model system, treatment of the cytochrome c-specific T cell hybridoma 2B4.11 in vitro with Ag in the context of histocompatible APC results in cellular activation, as shown by IL-2 release and growth inhibition. In vivo treatment with Ag results in tumor cell elimination as a result both of a direct inhibitory effect of cytochrome c that is mediated through the 2B4.11 TCR and to the induction of host immunity. In vivo lymphocyte-depletion studies showed that CD8-bearing cells were critical to the successful elimination of tumor cells mediated by Ag, whereas depletion of CD4-bearing cells had only minor effects on the outcome. Cytotoxic cells from mice cured by Ag treatment lysed only 2B4.11 among a panel of related tumors, although in vivo cross-protection studies showed that 2B4.11-immune mice were also resistant to the growth of BW5147 and C10.9. Because spleen cells from 2B4.11 immune mice did not recognize 2B4.11 or other related tumors in proliferation assays, we concluded that a participant(s) with memory and specificity, not assayed in vitro, was also involved in the mediation of the immune effects observed. For therapies based on the use of less selective agents, i.e. mAb that share the activating properties of Ag but can react with T cell neoplasms of unknown specificity, it would appear that a relatively intact immune system is required for maximal success.
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PMID:T cell tumor cure by T cell receptor-mediated activation requires the development of CD8-dependent host immunity. 215 71

We have evaluated the ability of a peptide-specific, I-Ak-restricted murine T hybridoma to bind its Ag in the presence and absence of class II MHC molecules. The restricting Ia molecule, when supplied as a plasma membrane preparation of I-Ak-expressing APC, specifically increases the avidity of the Ag-binding complex by lengthening its t1/2, without affecting the rate at which the complex is formed. Experiments using mutated I-Ak molecules indicate that the ability of a mutant Ia species to present Ag is distinct from its ability to stabilize the Ag-recognition complex, suggesting that T cell stimulation depends not only upon stabilization of Ag-TCR-Ia complexes, but also upon distinct Ia-influenced conformational signals.
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PMID:The role of Ia in the formation of a T cell antigen-recognition complex. 225 4

Resting B cells stimulated the proliferation of two T cell clones much less efficiently than T cell-depleted low-density APC. In contrast, low-density cells and resting B cells stimulated the clones to produce similar levels of inositol phosphates, a rapid biochemical event dependent only on occupancy of the TCR. The inefficient stimulation of T cell proliferation by resting B cell APC was dramatically improved by the addition of allogeneic low-density accessory cells incapable of being recognized by the TCR on the responding T cells. The results are most consistent with a model where low-density and resting B cell APC display similar amounts of Ag/Ia molecule complexes capable of being recognized by the TCR on the responding T cells but differ in the provision of costimulatory signals that, together with TCR occupancy, are required for IL-2 production.
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PMID:Antigen presentation by resting B cells. Effectiveness at inducing T cell proliferation is determined by costimulatory signals, not T cell receptor occupancy. 230 34

The activation of Ag-specific, Ia molecule-restricted, TCR V beta 3+ T cell clones by staphylococcal toxic shock syndrome toxin-1 (TSST-1), was investigated. The results show that although Ag- and TSST-1-induced activation of T cell clones both require TCR expression and similar biologic activation signals, the Ia molecule requirement for TSST-1 recognition was much less stringent than that observed for antigenic peptide recognition. In addition, T cell clones recognized TSST-1 without processing by APC. These results suggest that the ability of TSST-1 to polyclonally activate T cells is dependent on TCR recognition of the intact toxin molecule bound to a nonpolymorphic region(s) of the Ia molecule resulting in the same activation events induced by Ag recognition.
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PMID:Molecular requirements for T cell activation by the staphylococcal toxic shock syndrome toxin-1. 231 89

With the use of flow cytometry, we recorded changes in intracellular ionized calcium [Ca2+]i of Indo-1 loaded T cells that were triggered by contact with APC. This rapid readout of TCR perturbation enabled us to monitor the formation of stimulatory Ag-MHC complexes on EBV-transformed B cells that were either pulsed with native tetanus toxoid (TT) or with a 12-amino-acid fragment of this protein. Neither unpulsed APC nor Ag-specific APC that were pulsed with native Ag and kept at +4 degrees C were able to induce changes in basal T cell [Ca2+]i in TT-specific T cell clones. After 1 h at 37 degrees C, however, the Ag-pulsed APC were able to induce a three-to-fourfold increase in [Ca2+]i. This length of time appeared to be almost independent of the concentration of Ag with which the APC were pulsed, suggesting that the lag time was due more to intracellular transit than to association of the processed Ag with the MHC molecule. Furthermore, the same lag time and independence of Ag concentration were found when the EBV-transformed B cells were pulsed with a mouse-anti-transferrin receptor mAb and tested for their capacity to trigger a T cell clone specific for processed mouse Ig. This indicates that, in addition to surface Ig, other receptors that are internalized can function in the same fashion in the uptake and processing of a soluble Ag. In contrast to what was found with intact native Ag, no lag time was observed when the APC were pulsed with high concentrations of a 12-amino-acid peptide, containing the amino acid sequence recognized by a TT-specific T cell clone, suggesting that the formation of MHC-peptide complexes occurs instantly. Pulsing with a lower peptide concentration, however, caused the appearance of a time-dependent increase in efficacy of Ag presentation, suggesting a slow accumulation of MHC-peptide complexes on the B cell membrane.
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PMID:Kinetics of MHC-antigen complex formation on antigen-presenting cells. 245 65

Previous experiments have demonstrated that the immune response of MHC congenic mice to pigeon cytochrome c is under Ir gene control. Expression of I-E-encoded gene products influences both the magnitude and fine specificity of the Th cell response to pigeon cytochrome c and phylogenetic derivatives. Results of those experiments implicate both determinant selection and repertoire selection as mechanisms of Ir gene control in this system. In this report we have compared the TCR expressed in pigeon cytochrome c-reactive Th cells from B10.A(I-Ek), B10.A(5R) (I-Eb), and B10.S(9R) (I-Es) mice. The B10.A(5R) strain is a low responder to pigeon cytochrome c, but in response to moth cytochrome c this strain produces T cells which respond to pigeon or moth cytochrome c on B10.A APC. These cells are phenotypically identical to the predominant clonal phenotype seen in the B10.A response to pigeon cytochrome c. In this report, we show that the B10.A and B10.A(5R) pigeon cytochrome c-reactive T cells express essentially identical T cell receptors. These results, coupled with recent studies reporting a relatively low affinity for I-Eb molecules by pigeon cytochrome c peptides compared with moth cytochrome c peptides, strongly argue that the immune response defect in the B10.A(5R) strain is due to a defect in Ag presentation (determinant selection). In contrast, B10.A and B10.S(9R) strains are high responders to pigeon cytochrome c. Both strains produce T cell clones which are capable of responding to cytochrome c presented by either B10.A or B10.S(9R) APC in vitro. We show that, even in T cells with this MHC restriction degeneracy, the TCR expressed in the two strains are different. Because the APC of both strains can clearly present the cytochrome c Ag, we conclude that the differential expression of the TCR in the responses is due to a T cell repertoire selection difference in the two strains. Thus, for the response to one Ag in three MHC congenic strains, there exists evidence that both determinant selection and repertoire selection can be mechanisms of Ir gene control of an immune response.
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PMID:Two distinct mechanisms account for the immune response (Ir) gene control of the T cell response to pigeon cytochrome c. 245 67

The effect of human T cell leukemia/lymphoma virus type I (HTLV-I) infection on the function and the phenotype of a human proliferating/cytotoxic T cell clone, specific for tetanus toxin, was investigated. During the period after infection, two distinct phases were observed, based on growth properties, phenotype, and functional activity of the infected cells. Phase I HTLV-I infected cells (0 to about 150 days after infection) proliferated in an IL-2-dependent way, but without the requirement for repetitive antigenic stimulation. No differences in expression of the CD2, CD3, CD4, Tp103, and CD28 Ag between these cells and the parental cells could be demonstrated, with the exception of the expression of IL-R p55 and HLA-DR Ag, which were constitutively expressed on the phase I cells. The phase I HTLV-I-infected cells, as well as the parental 827 cells reacted with a mAb specific for an epitope on the variable part of the TCR beta-chain, indicating that the TCR was not altered after HTLV-I infection. Like the parental clone, the phase I cells proliferated in response to tetanus toxin, but the tetanus toxin-specific response of the phase I cells did not require the presence of APC. Results of experiments, in which the levels of intracellular Ca2+ were measured, indicated that HTLV-I cells can acquire the capability to process Ag and present that to themselves. Phase I HTLV-I-infected T cells had lost their cytotoxic activity which was likely to be due to an effect on the lytic machinery rather than on Ag recognition by the TCR, inasmuch as it was found that phase I HTLV-I-infected T cells did no longer contain N-alpha-benzyloxy-L-lysine thiobenzylester-serine esterase activity. Furthermore, it was found that phase I HTLV-I-infected T cells had a diminished capacity to form conjugates with target cells. From a period of about 200 days after HTLV-I infection, phase II cells emerged that proliferated strongly in the absence of IL-2 and that had lost all functional activity. These cells did not express the CD3/T cell receptor complex on their surface. Phase I as well as phase II HTLV-I-infected cells were targets for CTL raised in the autologous donor.
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PMID:Human T cell leukemia/lymphoma virus type I infection of a CD4+ proliferative/cytotoxic T cell clone progresses in at least two distinct phases based on changes in function and phenotype of the infected cells. 246 94


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