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Biomedical subjects

W R Heath

Publications and source records attributed to W R Heath.

At least 37 records · Page 2Linked to original sources
PubMed1999

Differential coupling of second signals for cytotoxicity and proliferation in CD8+ T cell effectors: amplification of the lytic potential by B7.

The role of second signals delivered through B7/CD28 interactions in T cell activation is well documented. However, once CTLs are elicited, TCR-mediated cytotoxicity appears to be uncoupled from the requirement for costimulatory signals. In this study, we show an uncoupling across a broad range of concentrations of peptide, thus demonstrating that cytolysis is a TCR-mediated response that is fully independent of costimulatory signals. However, the same T cell effectors remain fully responsive to B7 engagement, which is able to amplify Ag-mediated proliferation and cytolytic capacity. B7 expression by targets results in an IL-2-mediated proliferative expansion of the effectors concurrent with the elimination of the targets. Thus, costimulation of effectors results in a vast expansion in lytic units over time, which does not occur in the absence of IL-2 or B7. Both TCR-derived and second signals appear to be necessary to achieve this result. These results suggest that B7-expressing APC or a cohort of IL-2-producing helper cells would functionally extend the duration and effectiveness of the cytotoxic response occurring in localized immune responses.

Animals↗
PubMed1999

Ontogeny of T cell tolerance to peripherally expressed antigens.

Transgenic expression of the influenza virus hemagglutinin (HA) in the pancreatic islet beta cells of InsHA mice leads to peripheral tolerance of HA-specific T cells. To examine the onset of tolerance, InsHA mice were immunized with influenza virus A/PR/8 at different ages, and the presence of nontolerant T cells was determined by the induction of autoimmune diabetes. The data revealed a neonatal period wherein T cells were not tolerant and influenza virus infection led to HA-specific beta cell destruction and autoimmune diabetes. The ability to induce autoimmunity gradually waned, such that adult mice were profoundly tolerant to viral HA and were protected from diabetes. Because cross-presentation of islet antigens by professional antigen-presenting cells had been reported to induce peripheral tolerance, the temporal relationship between tolerance induction and activation of HA-specific T cells in the lymph nodes draining the pancreas was examined. In tolerant adult mice, but not in 1-week-old neonates, activation and proliferation of HA-specific CD8(+) T cells occurred in the pancreatic lymph nodes. Thus, lack of tolerance in the perinatal period correlated with lack of activation of antigen-specific CD8(+) T cells. This work provides evidence for the developmental regulation of peripheral tolerance induction.

Aging↗
PubMed1999

Signalling through CD30 protects against autoimmune diabetes mediated by CD8 T cells.

Autoantigens found on pancreatic islets can move to draining lymph nodes, where they are able to cause the activation and consequent deletion of autoreactive T cells by a mechanism termed cross-tolerance. This deletion depends on signalling through CD95 (also known as Fas), a member of the superfamily of tumour-necrosis-factor receptors. Here we describe a new mechanism that protects against autoimmunity: this mechanism involves another member of this superfamily, CD30, whose function was largely unknown. CD30-deficient islet-specific CD8-positive T cells are roughly 6,000-fold more autoaggressive than wild-type cells, with the transfer of as few as 160 CD30-deficient T cells leading to the complete destruction of pancreatic islets and the rapid onset of diabetes. We show that, in the absence of CD30 signalling, cells activated but not yet deleted by the CD95-dependent cross-tolerance mechanism gain the ability to proliferate extensively upon secondary encounter with antigen on parenchymal tissues, such as the pancreatic islets. Thus, CD30 signalling limits the proliferative potential of autoreactive CD8 effector T cells and protects the body against autoimmunity.

Adoptive Transfer↗
PubMed1999

Cytotoxic T lymphocyte activation by cross-priming.

Cross-priming represents the induction of cytotoxic T lymphocyte responses to exogenous, usually cell associated, antigens that are captured and re-presented on bone-marrow-derived antigen-presenting cells. For effective cross-priming, cytotoxic T lymphocytes require help from CD4(+) T cells, which mediate this help indirectly via modification of the antigen-presenting cell. Recent advances made in research into the cellular and molecular interactions required for cross-priming have greatly improved our understanding of the antigenic requirements for effective priming and have revealed a role for CD40 and its ligand in the provision of T cell help.

Animals↗
PubMed1999

Inhibition of naïve class I-restricted T cells by altered peptide ligands.

Amino acid variants of an antigenic peptide or altered peptide ligands have previously been investigated with CD4+ and CD8+ T cells. However, for CD8+ T cells, only clones (which are continually restimulated in vitro) have been assessed. Using TCR transgenic mice specific for a class I Kb-restricted OVA peptide (OVAp; OT-I mice) as a source of naïve CD8+ T cells, single amino acid variants of the OVAp were analysed in vitro for their ability to antagonize the proliferative and cytotoxic function of naïve OT-I cells. Peptides with substitutions at TCR contact residues were found to be the most potent antagonists of OT-I cell function. Those peptides that inhibited activation of cells to proliferate also inhibited activation of cells to become killers. Inhibition was inversely correlated with interferon (IFN)-gamma production. It was found that levels of antagonist peptide required for inhibition were higher than that described for T cell clones, presumably due to affinity differences.

Amino Acid Sequence↗
PubMed1999

The use of carboxyfluorescein diacetate succinimidyl ester to determine the site, duration and cell type responsible for antigen presentation in vivo.

This report examines the use of 5-(and-6)-carboxyfluorescein diacetate succinimidyl ester (CFSE) to determine the site, duration and cell type responsible for antigen presentation in vivo. Evidence that CFSE-labelled T cells can be used to determine where various types of antigens are presented, including auto-antigens, oral antigens and cell-associated foreign antigens, is provided. Using this technique, the length of time antigen is presented after acquisition by APC was measured. Finally, CFSE labelling was used to identify the origin of the APC responsible for different forms of antigen presentation.

Animals↗
PubMed1999

CD30 prevents T-cell responses to non-lymphoid tissues.

Self antigens can induce T-cell tolerance via a mechanism termed cross-tolerance. This involves the transfer of peripheral tissue antigens to professional APC for presentation in the draining lymph nodes. In this site, CD8+ T cells are activated, proliferate, and are slowly deleted by a CD95-dependent mechanism. Prior to their deletion, some activated cells leave the lymph nodes and encounter antigens on peripheral parenchymal tissues. Without functional CD30, these cells proliferate extensively and cause substantial tissue damage. Thus, CD30 limits autoreactivity, acting as a 'brake' on T-cell proliferation after recognition of autoantigens on parenchymal tissues.

Animals↗
PubMed1999

The cytotoxic T-cell response to herpes simplex virus type 1 infection of C57BL/6 mice is almost entirely directed against a single immunodominant determinant.

Many virus infections give rise to surprisingly limited T-cell responses directed to very few immunodominant determinants. We have been examining the cytotoxic T-lymphocyte (CTL) response to herpes simplex virus type 1 (HSV-1) infection. Previous studies have identified the glycoprotein B-derived peptide from residues 498 to 505 (gB(498-505)) as one of at least three determinants recognized by HSV-1-specific CTLs isolated from C57BL/6 mice. We had previously found that in vitro-derived CTLs directed to gB(498-505) show a characteristic pattern of T-cell receptor (TCR) usage, with 60% of gB(498-505)-specific CD8(+) T cells expressing BV10(+) TCR beta chains and a further 20% expressing BV8S1. In this report, we confirm that this TCR V-region bias is also reflected in the ex vivo response to HSV-1 infection. A high proportion of activated CD8(+) draining lymph node cells were found to express these dominant V regions, suggesting that a substantial number of in vivo responding T cells were directed to this one viral determinant. The use of an HSV-1 deletion mutant lacking the gB(498-505) determinant in combination with accurate intracellular gamma interferon staining allowed us to quantify the extent of gB-specific T-cell dominance. Together, these results suggested that between 70 and 90% of all CD8(+) HSV-1-specific T cells target gB(498-505). While deletion of this determinant resulted in an attenuated CD8(+) T-cell response, it also permitted the emergence of one or more previously unidentified cryptic specificities. Overall, HSV-1 infection of C57BL/6 mice results in an extremely focused pattern of CD8(+) T-cell selection in terms of target specificity and TCR expression.

Animals↗
PubMed1999

Oral administration of antigen can lead to the onset of autoimmune disease.

Oral administration of antigen is known to induce a state of specific immunological unresponsiveness to a subsequent challenge with the same antigen. Based on this, oral delivery of autoantigens has been applied as a possible strategy for the treatment of human autoimmune diseases like rheumatoid arthritis and multiple sclerosis. The precise mechanisms involved in the induction of oral tolerance are yet to be clearly defined. In an attempt to address this issue, we have generated several lines of transgenic mice using ovalbumin (OVA) as the model antigen. Our studies have shown that a cytotoxic T lymphocyte response could be induced by oral administration of antigen and that this could lead to the onset of autoimmune disease. These findings suggest caution should be applied when oral administration of antigen is used to treat human autoimmune diseases.

Administration, Oral↗
PubMed1998

B cells directly tolerize CD8(+) T cells.

This report investigates the response of CD8(+) T cells to antigens presented by B cells. When C57BL/6 mice were injected with syngeneic B cells coated with the Kb-restricted ovalbumin (OVA) determinant OVA257-264, OVA-specific cytotoxic T lymphocyte (CTL) tolerance was observed. To investigate the mechanism of tolerance induction, in vitro-activated CD8(+) T cells from the Kb-restricted, OVA-specific T cell receptor transgenic line OT-I (OT-I cells) were cultured for 15 h with antigen-bearing B cells, and their survival was determined. Antigen recognition led to the killing of the B cells and, surprisingly, to the death of a large proportion of the OT-I CTLs. T cell death involved Fas (CD95), since OT-I cells deficient in CD95 molecules showed preferential survival after recognition of antigen on B cells. To investigate the tolerance mechanism in vivo, naive OT-I T cells were adoptively transferred into normal mice, and these mice were coinjected with antigen-bearing B cells. In this case, OT-I cells proliferated transiently and were then lost from the secondary lymphoid compartment. These data provide the first demonstration that B cells can directly tolerize CD8(+) T cells, and suggest that this occurs via CD95-mediated, activation-induced deletion.

Animals↗
PubMed1998

Major histocompatibility complex class I-restricted cross-presentation is biased towards high dose antigens and those released during cellular destruction.

Naive T cells recirculate mainly within the secondary lymphoid compartment, but once activated they can enter peripheral tissues and perform effector functions. To activate naive T cells, foreign antigens must traffic from the site of infection to the draining lymph nodes, where they can be presented by professional antigen presenting cells. For major histocompatibility complex class I-restricted presentation to CD8+ T cells, this can occur via the cross-presentation pathway. Here, we investigated the conditions allowing antigen access to this pathway. We show that the level of antigen expressed by peripheral tissues must be relatively high to facilitate cross-presentation to naive CD8+ T cells. Below this level, peripheral antigens did not stimulate by cross-presentation and were ignored by naive CD8+ T cells, although they could sensitize tissue cells for destruction by activated cytotoxic T lymphocytes (CTLs). Interestingly, CTL-mediated tissue destruction facilitated cross-presentation of low dose antigens for activation of naive CD8+ T cells. This represents the first in vivo evidence that cellular destruction can enhance access of exogenous antigens to the cross-presentation pathway. These data indicate that the cross-presentation pathway focuses on high dose antigens and those released during tissue destruction.

Animals↗
PubMed1998

The peripheral deletion of autoreactive CD8+ T cells induced by cross-presentation of self-antigens involves signaling through CD95 (Fas, Apo-1).

Recently, we demonstrated that major histocompatibility complex class I-restricted cross-presentation of exogenous self-antigens can induce peripheral T cell tolerance by deletion of autoreactive CD8+ T cells. In these studies, naive ovalbumin (OVA)-specific CD8+ T cells from the transgenic line OT-I were injected into transgenic mice expressing membrane-bound OVA (mOVA) under the control of the rat insulin promoter (RIP) in pancreatic islets, kidney proximal tubules, and the thymus. Cross-presentation of tissue-derived OVA in the renal and pancreatic lymph nodes resulted in activation, proliferation, and then the deletion of OT-I cells. In this report, we investigated the molecular mechanisms underlying this form of T cell deletion. OT-I mice were crossed to tumor necrosis factor receptor 2 (TNFR2) knockout mice and to CD95 (Fas, Apo-1) deficient mutant lpr mice. Wild-type and TNFR2-deficient OT-I cells were activated and then deleted when transferred into RIP-mOVA mice, whereas CD95-deficient OT-I cells were not susceptible to deletion by cross-presentation. Furthermore, cross-presentation led to upregulation of the CD95 molecule on the surface of wild-type OT-I cells in vivo, consistent with the idea that this is linked to rendering autoreactive T cells susceptible to CD95-mediated signaling. This study represents the first evidence that CD95 is involved in the deletion of autoreactive CD8+ T cells in the whole animal.

Animals↗
PubMed1998

Help for cytotoxic-T-cell responses is mediated by CD40 signalling.

Cytotoxic T lymphocytes (CTLs) which carry the CD8 antigen recognize antigens that are presented on target cells by the class I major histocompatibility complex. CTLs are responsible for the killing of antigen-bearing target cells, such as virus-infected cells. Although CTL effectors can act alone when killing target cells, their differentiation from naive CD8-positive T cells is often dependent on 'help' from CD4-positive helper T (TH) cells. Furthermore, for effective CTL priming, this help must be provided in a cognate manner, such that both the TH cell and the CTL recognize antigen on the same antigen-presenting cell. One explanation for this requirement is that TH cells are needed to convert the antigen-presenting cell into a cell that is fully competent to prime CTL. Here we show that signalling through CD40 on the antigen-presenting cells can replace the requirement for TH cells, indicating that T-cell 'help', at least for generation of CTLs by cross-priming, is mediated by signalling through CD40 on the antigen-presenting cell.

Animals↗
PubMed1998

The threshold for autoimmune T cell killing is influenced by B7-1.

The concept that naive CD4+ and CD8+ T cells require co-stimulatory signals for activation and proliferation is well documented. Less clear is the need for co-stimulation during the effector phase of the T cell response. Here we examined the influence of B7-1 (CD80) during the effector phase of an autoimmune response to pancreatic islets using transgenic mouse lines which expressed B7-1 in either all or only some of their beta cells ("confluent" or "patchy" RIP-B7-1 mice). Transgenic expression of B7-1 in normal mouse islets that co-expressed the pro-inflammatory cytokine, IL-2, resulted in early spontaneous autoimmunity. Islets with IL-2 and "confluent" B7-1 expression were destroyed whereas islets with IL-2 and "patchy" B7-1 expression showed selective killing of the B7-1+ beta cells. Islet-reactive T cells, circulating in the RIP-B7-1/IL-2 mice, rejected syngeneic islet grafts, but only if these expressed B7-1. Introduction of the B7-1 transgene into the nonobese diabetic (NOD) genetic background likewise resulted in early spontaneous autoimmunity, but splenocytes from the diabetic animals could only transfer diabetes to NOD scid recipients that expressed B7-1 on their beta cells. In both these transgenic models, therefore, islet destruction required continuous B7-1 expression by target beta cells. Thus, although the normal repertoire contains T cells with potential islet reactivity, these T cells remain harmless because parenchymal cells like the beta cell cannot normally express B7-1. Our results also have implications for tumor immunotherapy in that the ability of T cells to kill poorly immunogenic targets may be dependent upon B7-1 expression by the target cell itself.

Animals↗
PubMed1998

Cross-presentation of self antigens to CD8+ T cells: the balance between tolerance and autoimmunity.

Upon encounter with foreign antigen, tissue-associated antigen-presenting cells (APCs) migrate to draining lymph nodes to prime specific T cells. Using the transgenic RIP-mOVA model, we recently demonstrated that self antigens derived from peripheral tissues are constitutively transported to draining lymph nodes, and can be presented in association with MHC class I molecules by a bone marrow-derived APC population. This form of class I-restricted presentation of exogenous antigen has been referred to as cross-presentation and can induce activation and proliferation of antigen-specific CD8+ T cells. In the absence of CD4+ T cell help, activation of CD8+ T cells is inefficient, and cross-presentation leads to peripheral deletion of autoreactive CD8+ T cells, acting as a mechanism to maintain self-tolerance. If CD4+ T cell help is available, CD8+ T cell responses to self antigens can be rendered immunogenic, leading to autoreactive responses. Whether autoimmunity results from such responses also depends on the tissue location of the antigen. In RIP-mOVA mice, which express the model antigen mOVA (a membrane-bound form of ovalbumin) in the pancreatic beta cells and kidney proximal tubules, OVA-specific CD8+ T cells, activated by cross-presentation, infiltrated the pancreas and caused B cell destruction. Interestingly, however, these cells did not infiltrate the kidney, suggesting that proximal tubular cells are to some extent protected from immune destruction. Analysis of the role of antigen concentration indicates that high doses were required for efficient cross-presentation, suggesting that this pathway is directed towards immune responses to high-dose antigens, such as may be present during viral infection.

Animals↗
PubMed1998

Defective TCR expression in transgenic mice constructed using cDNA-based alpha- and beta-chain genes under the control of heterologous regulatory elements.

We describe the generation of ovalbumin (OVA)-specific, MHC class II-restricted alpha beta T cell receptor (TCR) transgenic mice. Initial attempts at generating these transgenic mice utilized heterologous regulatory elements to drive the expression of cDNA genes encoding the separate alpha- and beta-chains of the TCR. Unexpectedly, T cells bearing the transgenic alpha beta TCR failed to emerge from the thymus in these mice, although the transgenes did modify endogenous TCR expression. However, subsequent modification of the approach which enabled expression of the TCR beta-chain under the control of its natural regulatory elements generated mice whose peripheral T cells expressed the transgenic TCR and were capable of antigen-dependent proliferation. These results show that successful generation of MHC class II-restricted, OVA-specific alpha beta TCR transgenic mice was dependent upon combining cDNA- and genomic DNA-based constructs for expression of the respective alpha- and beta-chains of the TCR.

Animals↗