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M K Jenkins

Publications and source records attributed to M K Jenkins.

At least 73 records · Page 4Linked to original sources
PubMed1991

IL-2 secretion and T cell clonal anergy are induced by distinct biochemical pathways.

In Th1 clones, TCR occupancy together with a costimulatory signal from APC results in IL-2 production. TCR occupancy alone results in unresponsiveness (anergy) to antigenic stimulation, a phenomenon that may be important for self-tolerance in vivo. Inasmuch as inositol phosphate production occurs during the induction of anergy other biochemical signals must be necessary for IL-2 production. Here we assess the role of tyrosine-specific protein kinases using the specific inhibitor, genistein. IL-2 secretion and responsiveness were very dependent on tyrosine-specific protein kinase activation and could be completely blocked under conditions where inositol phosphate generation occurred normally. Although anergy induction could also be blocked by inhibition of tyrosine-specific protein kinase activation this probably occurred indirectly via inhibition of inositol phospholipid hydrolysis. The differential susceptibility of IL-2 secretion and anergy induction to inhibition by genistein indicates that positive and negative outcomes of TCR occupancy may be mediated by distinct biochemical pathways.

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PubMed1991

A monoclonal antibody specific for a cytochrome c T cell stimulatory peptide inhibits T cell responses and affects the way the peptide associates with antigen-presenting cells.

A monoclonal antibody (mAb) specific for the 93-104 segment of pigeon cytochrome c (cyt) was shown to block interleukin 2 production and proliferation by pigeon cyt-specific T cells in response to the pigeon cyt 81-104 peptide using either the LK35.2 B cell hybridoma or normal splenocytes as antigen-presenting cells (APC). The mAb inhibited the response to soluble peptide antigen presented by metabolically inactive paraformaldehyde-fixed APC but not the response to APC that were pre-pulsed with Ag. These results suggest that the mAb blocked the formation of peptide-major histocompatibility complex (MHC) class II molecule complexes at the cell surface but did not displace the peptide once bound to the MHC class II molecule. As determined by direct binding experiments using labeled peptide, the major means of free peptide association with live APC was fluid-phase endocytosis. No free peptide associated directly with the MHC class II molecule at the cell surface near 0 degrees C since APC pulsed with peptide on ice did not activate cyt-specific T cells. The mAb enhanced the association of the radiolabeled peptide with APC at 4 degrees C apparently by binding of the peptide-mAb complex to Fc receptors. By stripping molecules from the LK35.2 cell surface using a nonspecific protease it was shown that the peptide-mAb complexes were not internalized either at 4 degrees C or 37 degrees C. Since the mAb was found to stably bind the peptide at pH levels below that of endosomes (pH 5.5-6.2) even if the peptide-mAb complexes were taken up by fluid-phase endocytosis, it is likely that the peptide would not be able to associate with MHC class II molecules inside the APC. This mAb appears to inhibit T cell activation by blocking the formation of peptide-MHC class II molecule complexes at the cell surface and by interfering with uptake of the peptide into endosomes. Therefore, it is different from other antibodies that have been reported to block T cell receptor recognition of preformed peptide/MHC class II molecule complexes.

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PubMed1991

Cell and receptor requirements for streptococcal pyrogenic exotoxin T-cell mitogenicity.

Streptococcal pyrogenic exotoxins (SPEs) A, B, and C, like other members of the pyrogenic toxin family, are able to cause toxic shock-like syndromes. One of the major properties of these toxins is the ability to induce T-cell proliferation. Characterization of T cell mitogenicity associated with SPEs A, B, and C was undertaken. SPEs A, B, and C were mitogenic for C57BL10/SnJ and BALB/cWAT T cells, with activities differing in intensity depending on the mouse strain and toxin employed. SPE-induced, T-cell-proliferative activity was dependent on class II major histocompatibility complex molecules expressed on antigen-presenting cells. The abilities of SPEs A, B, and C to preferentially stimulate murine cells with certain T-cell receptor V beta s were investigated by fluorescence-activated cell sorter analysis. SPE A preferentially activated T cells expressing V beta 8 but not V beta 3, 6, or 11, while SPEs B and C preferentially stimulated T cells which did not express any of the tested V beta s.

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PubMed1990

An intracellular calcium increase and protein kinase C activation fail to initiate T cell proliferation in the absence of a costimulatory signal.

Resting T lymphocytes proliferate in response to a combination of a calcium ionophore and a phorbol ester. This observation suggests that an increase in intracellular calcium free ion concentration [Ca2+]i and activation of protein kinase C (PKC) are sufficient signaling events for the initiation of T cell proliferation. In contrast, an accessory cell-generated costimulatory signal, acting independently of the rise in [Ca2+]i and PKC activation, is required for Ag-induced proliferation of type I T cell clones. We now report that this costimulatory signal is unexpectedly also being delivered via a cell-cell interaction during the response to ionomycin and phorbol ester. In the absence of this signal (at limiting cell numbers), T cells fail to divide. We also demonstrate that proliferation in response to immobilized anti-CD3 mAb requires the cell-cell interaction. These results suggest a model of T cell stimulation in which activation of a costimulatory signaling pathway is important in the regulation of the IL-2 gene, and only in the presence of this (third) signal can an increase in [Ca2+]i and PKC activity induce T cell proliferation. Such a model predicts that IL-2-dependent expansion of T cell clones in vivo in response to Ag receptor occupancy requires the delivery of an independent accessory cell-derived co-stimulatory signal.

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PubMed1990

Molecular requirements for T cell activation by the staphylococcal toxic shock syndrome toxin-1.

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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PubMed1990

Antigen presentation by resting B cells. Effectiveness at inducing T cell proliferation is determined by costimulatory signals, not T cell receptor occupancy.

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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PubMed1990

Inhibition of antigen-specific proliferation of type 1 murine T cell clones after stimulation with immobilized anti-CD3 monoclonal antibody.

The effect of stimulating normal type 1 murine T cell clones with anti-CD3 antibody was examined in vitro. In the absence of accessory cells, anti-CD3 antibody immobilized on plastic plates stimulated inositol phosphate production, suboptimal proliferation, IL-2 and IL-3 production, and maximal IFN-gamma production. Addition of accessory cells augmented lymphokine production and proliferation when the effects of "high-dose suppression" were relieved by removing the T cells from the antibody-coated plates. Exposure of type 1 T cell clones to immobilized anti-CD3 antibody alone rapidly induced long-lasting proliferative unresponsiveness (anergy) to Ag stimulation that could be prevented by accessory cells. This anergic state was characterized by a lymphokine production defect, not a failure of the T cells to respond to exogenous IL-2 or to express surface Ti/CD3 complexes. In addition, anergy could not be induced in the presence of cyclosporine A. These results suggest that under certain conditions anti-CD3 antibodies may have potent immunosuppressive effects independent of Ti/CD3 modulation. Furthermore, our results support a two-signal model of type 1 T cell activation in which Ti/CD3 occupancy alone (signal 1) induces anergy, whereas Ti/CD3 occupancy in conjunction with a costimulatory signal (signal 2) induces a proliferative response.

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PubMed1989

An accessory cell-derived costimulatory signal acts independently of protein kinase C activation to allow T cell proliferation and prevent the induction of unresponsiveness.

Presentation of Ag to type I CD4+ T cell clones by chemically fixed APC results in the induction of a long-lasting state of proliferative unresponsiveness in the T cell. Ag-specific TCR interactions do occur during this stimulation, as Ag- and Ia molecule-dependent increases in intracellular calcium free ion concentration can be demonstrated, yet free inositol phosphate generation is low and neither IL-2 synthesis nor proliferation occur. The addition of normal allogeneic accessory cells during this stimulation can restore the T cell proliferative response, as well as prevent the induction of unresponsiveness, thus defining an accessory cell-dependent costimulatory activity necessary for proliferation. We have now examined the biochemical effects of this costimulatory activity on early T cell activation. Normal accessory cell costimulatory activity was found to be incapable of augmenting the generation of free inositol phosphate in response to either fixed APC plus Ag or Con A alone. Furthermore, protein kinase C-dependent CD3 gamma-chain phosphorylation occurred in response to either fixed APC plus Ag or Con A alone, and the addition of normal accessory cells had no effect on the level of this phosphorylation. Finally, minimal CD3 zeta-chain tyrosine phosphorylation occurred during the induction of unresponsiveness with Ag and fixed APC alone and this also was not affected by the costimulatory activity. Our results demonstrate that T cell Ag receptor-mediated increases in intracellular calcium free ion concentration and protein kinase C activation occur independently of an accessory cell-derived costimulatory signal. In the absence of this costimulatory signal, these two intracellular second messengers are insufficient to induce a maximal proliferative response and in fact lead to a state of unresponsiveness.

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PubMed1988

Effect of gamma radiation on resting B lymphocytes. II. Functional characterization of the antigen-presentation defect.

The effect of radiation on three discrete Ag-presentation functions in resting B cells was examined: 1) Ag uptake and processing, 2) expression of processed Ag in the context of functional class II molecules, and 3) provision of necessary co-stimulatory, or "second," signals. Analysis of radiation's effect on B cell presentation of intact vs fragmented Ag or its effect on presentation by Ag-pulsed B cells indicated that damage to Ag uptake and processing could not account for the bulk of the radiation-induced Ag-presentation defect. Experiments with phosphatidylinositol hydrolysis as an indirect measure of TCR occupancy suggested that irradiation caused a fairly rapid (within 1 to 2 h) decrease in the ability of the B cell APC to display a stimulatory combination of Ag and class II molecule. Ag dose-response analyses demonstrated that when presenting a fragment of the Ag pigeon cytochrome c to a T cell clone, 3000 rad-treated B cell APC were able to stimulate approximately 50% as much phosphatidylinositol turnover as unirradiated B cells. It was also found that, in contrast to their inability to initiate T cell proliferation, and similarly to chemically cross-linked splenocytes, heavily irradiated resting B cells plus Ag induced a state of Ag hyporesponsiveness in T cell clones. This effect on T cells had the same Ag- and MHC-specificity as did receptor occupancy required for proliferation, indicating that heavily irradiated resting B cells bear functional class II molecules. Co-culture of T cells with allogeneic B cells and syngeneic heavily irradiated B cells or chemically cross-linked splenic APC plus Ag resulted in T cell proliferation and interfered with the induction of the hyporesponsive state. This co-stimulatory function was radiosensitive in resting allogeneic B cells. Together, these data support the hypothesis that the major functional consequences of radiation to resting B cell APC are a reduction in the effective display of Ag plus class II molecules and, probably what is more important, a loss in the ability to provide APC-derived co-stimulatory signals.

Animals↗
PubMed1988

Class II MHC-bearing keratinocytes induce antigen-specific unresponsiveness in hapten-specific Th1 clones.

Previous studies of Ia+ keratinocytes (KC) indicated that they functioned poorly or not at all when utilized as accessory cells for T cell activation. When Ia+ KC were modified with trinitrobenzene sulfonic acid, these cells did not induce a proliferative response in the TNP-specific, 1-Ek-restricted Th1 clone SE-4 (less than 5% of control). Analysis of supernatants generated from SE-4 cells incubated with these non-stimulatory accessory cells revealed low levels of IL-3 and IFN-gamma, but an absence of IL-2, when compared with supernatants generated from SE-4 cells stimulated with TNP-modified cultured Langerhans' cells that contain high levels of all of these lymphokines. Incubation of SE-4 cells with TNP-modified Ia+, but not Ia- KC or FITC-modified Ia+ KC, resulted in unresponsiveness to subsequent stimulation with TNP-modified functional accessory cells. Blocking studies with anti-class II MHC mAb revealed that the induction of unresponsiveness by hapten-modified Ia+ KC was restricted to the I-Ek molecule. Thus, the Ag and MHC specificities of unresponsiveness induced by TNP-modified Ia+ KC were identical to those observed for the proliferation of this clone in response to TNP-modified functional accessory cells. These data indicate the existence of a naturally occurring population of Ia+ cells that, after hapten-modification, induce an unresponsive state instead of proliferation of T cells.

Animals↗
PubMed1988

Effects of cyclosporine A on T cell development and clonal deletion.

Cyclosporine A (CsA) is an important immunosuppressive drug that is widely used in transplantation medicine. Many of its suppressive effects on T cells appear to be related to the inhibition of T cell receptor (TCR)-mediated activation events. Paradoxically, in certain situations CsA is responsible for the induction of a T cell-mediated autoimmunity. The effects of CsA on T cell development in the thymus were investigated to elucidate the physiologic events underlying this phenomenon. Two major effects were revealed: (i) CsA inhibits the development of mature single positive (CD4+8- or CD4-8+) TCR-alpha beta+ thymocytes without discernibly affecting CD4-8- TCR-gamma delta+ thymocytes and (ii) CsA interferes with the deletion of cells bearing self-reactive TCRs in the population of single positive thymocytes that do develop. This suggests a direct mechanism for CsA-induced autoimmunity and may have implications for the relative contribution of TCR-mediated signaling events in the development of the various T cell lineages.

Animals↗
PubMed1988

Allogeneic non-T spleen cells restore the responsiveness of normal T cell clones stimulated with antigen and chemically modified antigen-presenting cells.

Stimulation of IL-2-producing T cell clones with chemically modified APC and Ag induces a state of proliferative unresponsiveness, i.e., subsequent stimulation with normal APC and Ag fails to elicit IL-2 production. One possible effect of chemical modification on the APC is the destruction of its ability to provide costimulatory signals. To test this, various potential costimulators were added to T cells at the time of exposure to Ag and chemically modified APC. None of the cytokines tested, including IL-1, had a positive effect; however, addition of allogeneic spleen cells allowed a T cell proliferative response and prevented the induction of subsequent unresponsiveness. Fractionation of the spleen cells showed that low density B cells and macrophages were the best source of costimulatory activity. Allogeneic resting B cells provided some costimulatory activity and resting T cells, none at all. Attempts to mimic costimulatory signals with the phorbol ester PMA were only partially successful. PMA prevented the induction of T cell unresponsiveness but failed to allow T cell proliferation in response to Ag plus chemically modified APC. Our results suggest that IL-2 production by normal T cell clones is dependent not only on T cell receptor occupancy, but also on short range costimulatory signals that are provided to different degrees by various non-T accessory cells.

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PubMed1987

Antigen presentation by chemically modified splenocytes induces antigen-specific T cell unresponsiveness in vitro and in vivo.

We investigated the antigen specificity and presentation requirements for inactivation of T lymphocytes in vitro and in vivo. In vitro studies revealed that splenocytes treated with the crosslinker 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide (ECDI) and soluble antigen fragments failed to stimulate significant proliferation by normal pigeon cytochrome c-specific T cell clones, suggesting that the chemical treatment inactivated full antigen presentation function. However, T cell clones exposed to ECDI-treated splenocytes and antigen in vitro were rendered unresponsive for at least 8 d to subsequent antigen stimulation with normal presenting cells. As predicted by the in vitro results, specific T cell unresponsiveness was also induced in vivo in B10.A mice injected intravenously with B10.A, but not B10.A(4R), splenocytes coupled with pigeon cytochrome c via ECDI. The antigen and MHC specificity of the induction of this T cell unresponsiveness in vitro and in vivo was identical to that required for T cell activation. These results suggest that nonmitogenic T cell recognition of antigen/MHC on ECDI-modified APCs results in the functional inactivation of T cell clones.

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PubMed1987

Molecular events in the induction of a nonresponsive state in interleukin 2-producing helper T-lymphocyte clones.

Exposure of normal interleukin 2 (IL-2)-producing helper T-cell clones to antigen and 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide-treated antigen-presenting cells results in proliferative unresponsiveness to subsequent stimulation with antigen and normal antigen-presenting cells. In the present study, we have examined the molecular events that accompany the induction of this unresponsive state. T cells stimulated in this manner failed to produce IL-2, but interleukin 3, interferon-gamma, and IL-2 receptors were partially induced and T-cell receptor beta mRNA was fully induced. Although T-cell unresponsiveness correlated with an IL-2 production defect, addition of IL-2 during the induction phase failed to prevent development of the unresponsive state. The critical biochemical event appeared to be an increase in intracellular calcium. Removal of calcium from the medium prevented induction of the unresponsive state, whereas addition of the calcium ionophore ionomycin induced unresponsiveness as well as all of the related partial activation events. Thus, an increase in intracellular calcium under nonmitogenic conditions appears to initiate an alternative activation program that prevents the T cell from producing IL-2 in response to subsequent normal activation signals. The significance of this in vitro model for tolerance induction in vivo is discussed.

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