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Biomedical subjects

E Meinl

Publications and source records attributed to E Meinl.

At least 37 records · Page 2Linked to original sources
PubMed1998

Human myelin basic protein specific T cell lines display differential cytotoxicity against astrocytes, but are consistently cytotoxic against monocytes.

In experimental allergic encephalomyelitis (EAE) myelin basic protein (MBP) specific T cells differ in their encephalitogenic potential. To investigate the functional diversity of human MBP specific T cell lines, we analysed their cytotoxic activity against human astrocytes and monocytes. Five out of 14 MBP specific T cell lines killed astrocytes in the presence of MBP. Nevertheless, all lines lysed blood derived monocytes. T cell lines that lysed astrocytes efficiently in the presence of MBP, recognized peptide aa 80-99/86-105 in context with HLA-DRB5 * 0101, peptide aa 50-69/61-83 in context with HLA-DRB1 * 1501 and peptides aa 139-153, and aa 148-162 in context with HLA-DRB1 * 0101. There was no correlation of MBP-mediated lysis of astrocytes with TCR-Vbeta usage, HLA-restriction and the production of tumor-necrosis-factor-alpha (TNF-alpha), lymphotoxin (LT) and interferon-gamma (IFN-gamma). Different lysis of astrocytes, however, revealed a functional heterogeneity of MBP specific T cells, which was not observed by using monocytes as targets.

Astrocytes↗
PubMed1998

Impairment of mycobacterial immunity in human interleukin-12 receptor deficiency.

In humans, interferon gamma (IFN-gamma) receptor deficiency leads to a predisposition to mycobacterial infections and impairs the formation of mature granulomas. Interleukin-12 (IL-12) receptor deficiency was found in otherwise healthy individuals with mycobacterial infections. Mature granulomas were seen, surrounded by T cells and centered with epithelioid and multinucleated giant cells, yet reduced IFN-gamma concentrations were found to be secreted by activated natural killer and T cells. Thus, IL-12-dependent IFN-gamma secretion in humans seems essential in the control of mycobacterial infections, despite the formation of mature granulomas due to IL-12-independent IFN-gamma secretion.

Animals↗
PubMed1998

Anti-apoptotic strategies of lymphotropic viruses.

Induction of apoptosis of virus-infected cells is an important host cell defence mechanism. However, some viruses have incorporated genes that encode anti-apoptotic proteins or modulate the expression of cellular regulators of apoptosis. Here, Edgar Meinl and colleagues discuss recent evidence that viral interference with host cell apoptosis leads to enhanced viral replication, and to evasion of cytotoxic T-cell effects.

Apoptosis↗
PubMed1998

The fight of viruses against apoptosis.

The induction of apoptosis of virus-infected cells is an important host defense mechanism against invading pathogens. Some viruses express anti-apoptotic proteins that efficiently block apoptosis induced by death receptors or in response to stress signaled through mitochondria. Viral interference with host cell apoptosis leads to enhanced viral replication and may promote cancer.

Animals↗
PubMed1998

Herpesvirus saimiri transforms human T-cell clones to stable growth without inducing resistance to apoptosis.

Herpesvirus saimiri (HVS) transforms human T cells to stable growth in vitro. Since HVS codes for two different antiapoptotic proteins, growth transformation by HVS might be expected to confer resistance to apoptosis. We found that the expression of both viral antiapoptotic genes was restricted to cultures with viral replication and absent in growth-transformed human T cells. A comparative examination of HVS-transformed T-cell clones and their native parental clones revealed that the expression of Bcl-2, Bcl-X(L), Bax, and members of the tumor necrosis factor receptor (TNF-R) superfamily with a death domain, namely, TNF-RI, CD95, and TRAMP, were not modulated by HVS. Expression of CD30 was induced in HVS-transformed T cells, and these cells also expressed the CD30 ligand. Uninfected and transformed T cells were sensitive to CD95 ligation but resistant to apoptosis mediated by TRAIL or soluble TNF-alpha. CD95 ligand was constitutively expressed on transformed but not uninfected parental T cells. Both cell types showed similar sensitivity to cell death induction or inhibition of T-cell activation mediated by irradiation, oxygen radicals, dexamethasone, cyclosporine, and prostaglandin E2. Altogether, this study strongly suggests that growth transformation by HVS is based not on resistance to apoptosis but, rather, on utilization of normal cellular activation pathways.

Animals↗
PubMed1998

Antiapoptotic activity of the herpesvirus saimiri-encoded Bcl-2 homolog: stabilization of mitochondria and inhibition of caspase-3-like activity.

Viruses have evolved different strategies to interfere with host cell apoptosis. Herpesvirus saimiri (HVS) and other lymphotropic herpesviruses code for proteins that are homologous to the cellular antiapoptotic Bcl-2. In this study HVS-Bcl-2 was stably expressed in the human leukemia cell line Jurkat and in the murine T-cell hybridoma DO to assess its antiapoptotic spectrum and to gain further insight into its mode of action. HVS- Bcl-2 prevented apoptosis that occurs as a result of a disturbance of intracellular homeostasis by, for example, DNA damage or menadione, which gives rise to oxygen radicals. In Jurkat cells, HVS-Bcl-2 also inhibited apoptosis mediated by the death receptor CD95. In DO cells, HVS-Bcl-2 did not interfere with CD95-mediated apoptosis but blocked dexamethasone-induced cell death. Mitochondrial damage is a central coordinating event in apoptosis induced by different stimuli. To assess the integrity of mitochondria, we used rhodamine 123, which is released upon disturbance of the mitochondrial membrane potential, and determined the release of cytochrome c into the cytosol. Both signs of mitochondrial damage were prevented by HVS-Bcl-2. This viral protein also inhibited the generation of caspase-3-like DEVDase activity and blocked the cleavage of poly(ADP-ribose) polymerase, a natural substrate of caspase-3-like proteases. In conclusion, HVS-Bcl-2 protects against a great variety of apoptotic stimuli, stabilizes mitochondria, and acts upstream of the generation of caspase-3-like activity.

Apoptosis↗
PubMed1997

Identification of naturally processed T cell epitopes from glutamic acid decarboxylase presented in the context of HLA-DR alleles by T lymphocytes of recent onset IDDM patients.

Glutamic acid decarboxylase (GAD) has been defined as a major target antigen in insulin-dependent diabetes mellitus (IDDM). To identify the molecular ligands triggering a T cell response to GAD, a panel of human GAD65-specific T lymphocyte lines was generated from peripheral blood of three recent onset IDDM patients. All lines derived from a patient expressing the high-risk-conferring HLA-DR*0301/ *0401 haplotypes recognized a single epitope localized between amino acid positions 270 and 283 of GAD65, a stretch that is located in close proximity to the homology region shared with Coxsackie virus P2-C protein. All lines with this specificity were restricted to the DRA, B1*0401 product of the DR4 haplotype. Analysis of the GAD-specific T cell response in a second patient homozygous for DR4 haplotypes demonstrated that the same DRA, B1*0401 allele selected T cells specific for a different determinant. The T cell response profile in a third patient showed that DR*1501/ *1601-encoding haplotypes could present at least three different epitopes to GAD65-specific T lymphocytes. One of these epitopes was presented by a DR allele associated with the resistance-conferring DRB1*1501 haplotype. GAD-specific T cell lines could not be isolated from HLA class II-matched normal individuals. Our data reveal that (a) the T cell response to GAD65 is quite heterogenous in recent onset IDDM patients; (b) HLA-DR, not DQ, seems to be the principal restriction element used by T cells present at the onset of the disease; and (c) T cells responding to epitopes containing identical sequences to Coxsackie virus P2-C protein were not detected.

Alleles↗
PubMed1997

Viral FLICE-inhibitory proteins (FLIPs) prevent apoptosis induced by death receptors.

Viruses have evolved many distinct strategies to avoid the host's apoptotic response. Here we describe a new family of viral inhibitors (v-FLIPs) which interfere with apoptosis signalled through death receptors and which are present in several gamma-herpesviruses (including Kaposi's-sarcoma-associated human herpesvirus-8), as well as in the tumorigenic human molluscipoxvirus. v-FLIPs contain two death-effector domains which interact with the adaptor protein FADD, and this inhibits the recruitment and activation of the protease FLICE by the CD95 death receptor. Cells expressing v-FLIPs are protected against apoptosis induced by CD95 or by the related death receptors TRAMP and TRAIL-R. The herpesvirus saimiri FLIP is detected late during the lytic viral replication cycle, at a time when host cells are partially protected from CD95-ligand-mediated apoptosis. Protection of virus-infected cells against death-receptor-induced apoptosis may lead to higher virus production and contribute to the persistence and oncogenicity of several FLIP-encoding viruses.

Adaptor Proteins, Signal Transducing↗
PubMed1997

Growth transformation of antigen-specific T cell lines from rhesus monkeys by herpesvirus saimiri.

This study aims in establishing the in vitro basis for a primate model to evaluate potential applications of H. saimiri-transformed T cells. T cell lines specific for myelin basic protein and streptolysin O were derived from rhesus monkeys and transformed to stable antigen-independent growth with strain C488 of H. saimiri. The transformed T cells from rhesus monkeys did not produce infectious virus and harbored the H. saimiri genome exclusively in an episomal form, whereas transformed T cells from the New World monkey Calltithrix jacchus released infectious virus. Transformed T cells from rhesus monkeys showed an unaltered surface expression of CD2 and CD3, of the activation markers CD25 and CD69, and of the costimulatory molecule CD80 (B7.1). Remarkably, both transformed and nontransformed T cell lines were largely double-positive for CD4 and CD8. In contrast to the parental cell lines, the transformed cells constitutively expressed major histocompatibility complex-DR antigens and were able to present antigen to each other. The transformed T cells from rhesus monkeys continued to express a functionally intact T cell receptor and responded to recognition of their antigen with enhanced proliferation and production of Th1-type cytokines. In conclusion, H. saimiri-transformed rhesus monkey T cells may open a way to primate models for adoptive immunotherapy and studies on the pathogenesis of autoaggressive T cells.

Animals↗
PubMed1997

Activation induces apoptosis in Herpesvirus saimiri-transformed T cells independent of CD95 (Fas, APO-1).

Signaling via the T cell receptor (TCR)/CD3 complex of pre-activated T cells induces apoptosis. Such an activation-induced cell death (AICD) is thought to play an important role in the regulation of cellular immune responses. In this study we analyzed pathways of AICD by using human T cells transformed by Herpesvirus saimiri. These growth-transformed T cells show the phenotype of activated mature T cells and continue to express a functionally intact TCR. We show that human H. saimiri-transformed T cell clones readily undergo cell death upon signaling via the TCR/CD3 complex or via phorbol 12-myristate 13-acetate (PMA) + ionomycin. The AICD in H. saimiri-transformed T cells was detectable a few hours after activation and it was not affected by the presence of interleukin (IL)-2 or by anti-CD4 cross-linking. However, AICD required tyrosine phosphorylation, since it could be blocked by herbimycin A. Cyclosporin A (CsA) did not block the development of AICD, but other consequences of activation in H. saimiri-transformed T cells like the production of interferon-gamma. Surprisingly, the development of AICD was not reduced by neutralizing antibodies to tumor necrosis factor (TNF)-alpha or blocking antibodies directed to CD95 (Fas, APO-1), although H. saimiri-transformed T cells were sensitive to CD95 ligation. To confirm that this form of AICD is really independent of CD95, we have established an H. saimiri-transformed T cell line from a patient with a homozygous deletion in the CD95 gene. This CD95-deficient T cell line was as sensitive to AICD as other CD95-expressing H. saimiri-transformed T cells. In conclusion, we describe here a type of AICD in H. saimiri-transformed T cells that is independent of CD95 and TNF-alpha, not sensitive to CsA, but requires tyrosine phosphorylation. This system should be useful for the investigation of CD95-independent forms of AICD.

Apoptosis↗
PubMed1997

Functional phenotype of transformed human alphabeta and gammadelta T cells determined by different subgroup C strains of herpesvirus Saimiri.

Based on sequence divergence in the transformation-relevant region, herpesvirus saimiri strains are classified into three subgroups. Only members of subgroup C transform human T lymphocytes to continuous interleukin-2-dependent growth in culture. In this study, human cord blood T cells were immortalized by using different subgroup C strains (C488, C484, and C139). The resulting T-cell lines represented different types of T-cell clones. They were either CD4+ or CD8+ and expressed either the alphabeta or the gammadelta type of T-cell receptors. If transformed by the same virus strain, alphabeta and gammadelta clones were similar with respect to viral persistence, virus gene expression, proliferation, and Th1-type cytokine production. However, major differences were observed in T cells immortalized by different subgroup C strains. Strain C139 persisted at low copy number, compared to the high copy number of prototype C488. The transformation-associated genes stpC and tip of strain C488 were strongly induced after T-cell stimulation. The homologous genes of strain C139 were only weakly expressed and not induced after activation. After CD2 ligation, the C488-transformed T cells produced interleukin-2, whereas the C139-transformed cells did not. Correspondingly, the C139-transformed T cells were less sensitive to cyclosporin A. Sequence comparison from different subgroup C strains revealed a variability of the stpC/tip promoter region and of the Lck-binding viral protein Tip. Thus, closely related subgroup C strains of herpesvirus saimiri cause major differences in the functional phenotype of growth-transformed human T cells.

Amino Acid Sequence↗
PubMed1995

Activation of a myelin basic protein-specific human T cell clone by antigen-presenting cells from rhesus monkeys.

This study addresses the capacity of peripheral blood mononuclear cells (PBMC) from rhesus monkeys (Macaca mulatta) to present myelin basic protein (MBP), a candidate auto-antigen for multiple sclerosis, to MBP-specific human CD4+ T cell clones. MHC-restriction of the human T cell clones was determined with HLA-DR-transfected L cells, and epitope specificity was established with a panel of overlapping 20-mer peptides. The MHC-DR region of the rhesus monkeys (Mamu) was characterized serologically and by sequence analysis. We identified one CD4+ HLA-DRB1*0301-restricted Th1-like human T cell clone (ES-BP8) that was activated to proliferation with human or rhesus monkey MBP, or peptide MBP 29-48 presented by PBMC from six different rhesus monkeys expressing the Mamu-DRB1*0305 or -DRB1*0306 alleles. After transformation to continuous growth with Herpesvirus saimiri, the T cell clone could still be stimulated by antigen (Ag) and Ag-presenting cells (APC) from monkeys. Two other T cell clones with the same HLA-restriction and the same peptide-specificity did not respond to MBP presented by these rhesus monkeys. The exon 2 sequences HLA-DRB1*0301, Mamu-DRB1*0305 and -DRB1*0306 differ at positions 32, 47, 67, 73 and 86. These amino acid differences are not critical for the binding of MBP 29-48 and do not abrogate recognition by the clone ES-BP8, but interfere with the recognition of the two other HLA-DRB1*0301-restricted T cell clones. In conclusion, studying Ag-presentation from rhesus monkey may provide further insight into the interaction of antigenic peptide, TCR and MHC.(ABSTRACT TRUNCATED AT 250 WORDS)

Alleles↗
PubMed1995

The role of autoimmune T lymphocytes in the pathogenesis of multiple sclerosis.

Autoimmune T cells play a key role as regulators and effectors of autoimmune disease. In multiple sclerosis (MS), activated T cells specific for myelin components or other locally expressed autoantigens enter the CNS and recognize their antigen(s) on local antigen-presenting cells. After local stimulation, the T cells produce a plethora of cytokines and inflammatory mediators that have profound effects on the local cellular environment, induce and recruit additional inflammatory cells, and contribute to myelin damage. An increasingly detailed knowledge of these processes will greatly facilitate the development of new immunotherapies. This article focuses on the role of T cells in MS. We provide a brief overview of the principles of T-cell immunology, discuss the experimental techniques available for studying T cells, address the role of T cells in the pathogenesis of MS, and highlight modern concepts for immunotherapy.

Amino Acid Sequence↗
PubMed1994

Refolding of human class II major histocompatibility complex molecules isolated from Escherichia coli. Assembly of peptide-free heterodimers and increased refolding-yield in the presence of antigenic peptide.

The alpha- and beta-chains of the heterodimeric major histocompatibility complex molecules HLA-DRB5*0101 and DRB1*0101 were expressed separately in Escherichia coli. The cytoplasmic and membrane-spanning domains of both chains were replaced by oligohistidine tags to allow purification by metal chelate chromatography. The recombinant proteins were refolded to peptide-free, water-soluble heterodimers by removal of major amounts of detergents and concomitant reoxidiation of disulfide bonds. Correct conformation was documented by three criteria: (a) affinity binding experiments using the antibody L243, which is known to recognize a conformational epitope formed only by correctly associated heterodimers; (b) specific binding of peptides to the refolded molecules; (c) recognition of peptides bound to refolded HLA-DR molecules by T-cells as reflected by Ca2+ influx into T-cells and production of interferon-gamma. The refolding reaction did not absolutely depend on the presence of peptides. The yield of peptide-free heterodimers was 3.0%. However, the yield of refolded heterodimer was increased to 10% if refolding was performed in the presence of antigenic peptides.

Amino Acid Sequence↗
PubMed1994

Human astrocytes are only partially competent antigen presenting cells. Possible implications for lesion development in multiple sclerosis.

Highly purified astrocyte cultures from human embryonic brain were examined for their capacity to present antigen to human leukocyte antigen (HLA) class II compatible, cytolytic CD4+ T lymphocytes. Most astrocytes constitutively expressed HLA class I products and LFA-3 (CD58). Constitutive expression of HLA class II, LFA-1 alpha (CD11a) and ICAM-1 (CD54) was lower and varied among different cultures, while LFA-2 (CD2) was absent. IFN-gamma alone or in combination with TNF-alpha strongly enhanced expression of HLA class I, HLA-DR, -DP, -DQ, LFA-1 alpha and ICAM-1, but did not affect expression of LFA-2 (CD2) and LFA-3 (CD58). TNF-alpha alone induced only HLA class I and ICAM-1, but not HLA class II or LFA-1 alpha. Cytokine treated, but not untreated astrocytes were able to present protein (auto-)antigens to specific T lymphocyte lines. Astrocytes expressing appropriate major histocompatibility complex class II products were lysed by CD4+ T cells specific for myelin basic protein or tetanus toxoid. The lytic response was antigen dose dependent and HLA-DR restricted. It could be blocked by antibodies against HLA-DR determinants and against the adhesion molecules LFA-1 alpha and ICAM-1. In remarkable contrast to their susceptibility to T cell lysis, antigen presenting astrocytes were not only completely unable to induce T cell proliferation but even inhibited proliferation. The results indicate that, although human astrocytes have the potential to present protein antigens to CD4+ T cells, they do not induce the co-stimulatory factors required to trigger the complete T cell activation programme.

Antigen-Presenting Cells↗
PubMed1994

Multiple sclerosis. Immunomodulatory effects of human astrocytes on T cells.

Using a human culture system, we have previously shown that interferon-gamma-and tumour necrosis factor-alpha-stimulated astrocytes are capable of presenting antigens to T lymphocytes, but do not support antigen-dependent T cell proliferation. To gain further insight into the mechanisms involved in the local regulation of intracerebral T cell responses, we have investigated the effects of astrocytes on T cell proliferation induced by peripheral blood-derived mononuclear cells (PBMC). We found that astrocytes derived from human embryonic brain were able to suppress PBMC-dependent proliferation of antigen-specific, CD4+ T cell lines. Interferon-gamma production by PBMC-stimulated T cells was also suppressed by astrocytes, and this inhibition was seen as early as 6 h after initiation of co-culture. The inhibitory effect was observed in the presence of both HLA matched and mismatched astrocytes and was mediated by astrocyte-derived soluble factor(s) rather than by direct cellular contact. Inhibition of T cell proliferation was incompletely reverted by indomethacin, suggesting that prostaglandins were partially involved in the suppressive effect. The cytotoxic mediator nitric oxide was not involved in astrocyte-mediated inhibition. These observations led us to further investigate the contribution of other mediators known to down-regulate inflammatory processes. Our astrocyte cultures did not synthesize interleukin (IL)-4 or IL-10, whereas they secreted both the latent and active forms of transforming growth factor-beta 2. Transforming growth factor-beta was, however, found not to participate in astrocyte-induced inhibition in vitro. The inhibitory properties of human astrocytes may contribute to confinement of inflammatory lesions in multiple sclerosis and other inflammatory diseases of the central nervous system.

Astrocytes↗