Biomedical subjects

B Hemmer

Publications and source records attributed to B Hemmer.

At least 37 records · Page 2Linked to original sources

PubMed2000

Decrypting the spectrum of antigen-specific T-cell responses: the avidity repertoire of MBP-specific T-cells.

Myelin basic protein (MBP) is a well-characterized autoantigen potentially involved in the pathogenesis of the most common human demyelinating disease of the central nervous system (CNS), multiple sclerosis (MS). It is known that MBP-specific T-cell responses differ widely among different individuals and also within a single donor in terms of fine specificity and functional characteristics including the avidity in antigen recognition. In this report, we demonstrate that the in vitro selection of MBP-reactive T-cell repertoire is strictly dependent upon the antigen dose used in the primary cultures. MBP-specific T-cell lines (TCLs) were generated from MS patients and healthy donors using different antigen concentration in cultures (0.1 to 50 microg/ml). In both MS patients and controls, the number of obtained T-cell lines was affected by the antigen concentration. In addition, low and high antigen concentrations selected in vitro different T-cell populations in terms of peptide specificity patterns and different functional avidities in antigen recognition. Low concentrations of MBP in the primary cultures yielded a small number of TCLs recognizing the specific antigen with higher avidity whereas high antigen concentrations allowed the in vitro expansion of a higher numbers of T-cells recognizing MBP with lower avidity. The use of different antigen concentrations in the primary cultures can be applied as a simple experimental system to investigate the overall avidity repertoire of antigen-specific T-cell response in humans.

Antibody Affinity↗

PubMed2000

Dipeptidyl peptidase IV (CD26): role in T cell activation and autoimmune disease.

The ectoenzyme dipeptidyl peptidase IV (DP IV; EC 3.4.14.5; CD26) has been shown to play a crucial role in T cell activation. In the present study, we show by flow cytometry and by enzymatic DP IV assay that myelin basic protein (MBP)-specific, CD4+ T cell clones (TCC) derived from patients with multiple sclerosis (MS) express high levels of DP IV/CD26. The enzymatic activity of resting TCC was found to be three to fourfold higher than on resting peripheral blood T cells and close to that of T cells 48 hours after PHA stimulation. The DP IV inhibitors Lys[Z(NO2)]-thiazolidide and Lys[Z(NO2)]-pyrrolidide suppress in a dose-dependent manner DNA synthesis and IFN-gamma, IL-4, and TNF-alpha production of the antigen-stimulated TCC. These data suggest that CD26 plays a role in regulating activation of autoreactive TCC. Further in vivo investigations will clarify, whether the inhibition of the enzymatic activity of DP IV could be a useful tool for therapeutic interventions in MS and/or other autoimmune diseases.

Autoimmune Diseases↗

PubMed2000

A point mutation in PTPRC is associated with the development of multiple sclerosis.

Multiple sclerosis (MS) is the most common demyelinating disease of the central nervous system. It is widely accepted that a dysregulated immune response against brain resident antigens is central to its yet unknown pathogenesis. Although there is evidence that the development of MS has a genetic component, specific genetic factors are largely unknown. Here we investigated the role of a point mutation in the gene (PTPRC) encoding protein-tyrosine phosphatase, receptor-type C (also known as CD45) in the heterozygous state in the development of MS. The nucleotide transition in exon 4 of the gene locus interferes with mRNA splicing and results in altered expression of CD45 isoforms on immune cells. In three of four independent case-control studies, we demonstrated an association of the mutation with MS. We found the PTPRC mutation to be linked to and associated with the disease in three MS nuclear families. In one additional family, we found the same variant CD45 phenotype, with an as-yet-unknown origin, among the members affected with MS. Our findings suggest an association of the mutation in PTPRC with the development of MS in some families.

Base Sequence↗

PubMed2000

Minimal peptide length requirements for CD4(+) T cell clones--implications for molecular mimicry and T cell survival.

CD4(+) T lymphocytes usually recognize peptides of 12-16 amino acids in the context of HLA class II molecules. We have recently used synthetic peptide combinatorial libraries to dissect in detail antigen recognition by autoreactive CD4(+) T cell clones (TCC). The results of these studies demonstrated that antigen recognition by T cells is highly degenerate and that many cross-reactive ligands can be defined, some of which much more potent than the selecting autoantigen. Based on these observations, we examined the response of a myelin basic protein-specific HLA class II-restricted CD4(+) TCC to truncation variants of optimal ligands. Surprisingly, pentapeptides, tetrapeptides and even tripeptides derived from different segments of the optimal ligands were recognized by the TCC, and some were even more potent than the selecting autoantigen. In addition, these peptides enhanced the survival of the TCC at low concentration. The relevance of this finding was supported by the generation of pentapeptide-specific CD4(+) TCC from peripheral blood lymphocytes. These observations not only change existing views on the length requirements for activation of CD4(+) HLA class II-restricted T cells, but also extend our knowledge about the flexibility of TCR recognition and the potential for cross-reactivity in the immune system.

Antigen Presentation↗

PubMed1999

Immunogenicity. I. Use of peptide libraries to identify epitopes that activate clonotypic CD4+ T cells and induce T cell responses to native peptide ligands.

Recent studies have demonstrated the utility of synthetic combinatorial libraries for the rapid identification of peptide ligands that stimulate clonotypic populations of T cells. Here we screen a decapeptide combinatorial library arranged in a positional scanning format with two different clonotypic populations of CD4+ T cells to identify peptide epitopes that stimulate proliferative responses by these T cells in vitro. An extensive collection of mimic peptide sequences was synthesized and used to explore the fine specificity of TCR/peptide/MHC interactions. We also demonstrate that many of these deduced ligands are not only effective immunogens in vivo, but are capable of inducing T cell responses to the original native ligands used to generate the clones. These results have significant implications for considerations of T cell specificity and the design of peptide vaccines for infectious disease and cancer using clinically relevant T cell clones of unknown specificity.

Amino Acid Sequence↗

PubMed1999

Serial TCR engagement and down-modulation by peptide:MHC molecule ligands: relationship to the quality of individual TCR signaling events.

In the present study, we examined the relationships among quantitative aspects of TCR engagement as measured by receptor down-modulation, functional responses, and biochemical signaling events using both mouse and human T cell clones. For T cells from both species, ligands that are more potent in inducing functional responses promote TCR down-modulation more efficiently than weaker ligands. At low ligand density, the number of down-modulated TCR exceeds the number of available ligands by as much as 80-100:1 in the optimal human case, confirming the previous description of serial ligand engagement of TCR (Valitutti, et al. 1995. Nature 375:148-151). A previously unappreciated relationship involving TCR down-modulation, the pattern of proximal TCR signaling, and the extent of serial engagement was revealed by analyzing different ligands for the same TCR. Functionally, more potent ligands induce a higher proportion of fully tyrosine phosphorylated zeta-chains and a greater amount of phosphorylated ZAP-70 than less potent ligands, and the number of TCR down-modulated per available ligand is higher with ligands showing this full agonist-like pattern. The large number of receptors showing partial zeta phosphorylation following exposure to weak ligands indicates that the true extent of TCR engagement and signaling, and thus the amount of sequential engagement, is underestimated by measurement of TCR down-modulation alone, which depends on full receptor activation. These data provide new insight into T cell activation by revealing a clear relationship among intrinsic ligand quality, signal amplification by serial engagement, functional T cell responses, and observable TCR clearance from the cell surface.

Amino Acid Sequence↗

PubMed1999

Molecular mimicry and multiple sclerosis: degenerate T-cell recognition and the induction of autoimmunity.

Various mechanisms have been proposed for the initiation of autoimmune responses by autoreactive T-cell clones. One of these, the molecular mimicry hypothesis, postulates that myelin-reactive T-cell clones are activated by foreign antigens. Until recently, sequence homology between self- and foreign antigens was considered necessary for cross-recognition to occur in multiple sclerosis. This article reviews current progress in T-cell receptor immunology that led to modify this view and proposes a role for degenerate T-cell antigen recognition in the induction of autoimmunity.

Amino Acid Sequence↗

PubMed1999

Molecular mimicry and multiple sclerosis--a possible role for degenerate T cell recognition in the induction of autoimmune responses.

Multiple sclerosis is an inflammatory demyelinating disease of the central nervous system. The etiology is unknown, but several lines of evidence support the hypothesis that the pathogenesis is mediated by autoreactive T lymphocytes. Molecular mimicry has been proposed as a possible mechanism for the development of an autoimmune response to myelin antigens. According to this model, an immune reaction to self antigens could be initiated by T cells that cross-react with infectious agents that "mimic" the autoantigen, i.e. they share immunologic epitopes. It was previously thought that, in order for a cross-reaction of T cells to two different antigens to occur, a substantial amino acid sequence homology between the two antigens was required. More recent studies on the basic mechanisms of T cell antigen recognition have shown that, at least for some T cell clones, antigen recognition is more "degenerate" and sequence homology is not required for crossreactivity to occur. This article reviews the relevance of these recent advances in basic T cell receptor immunology to the occurrence of autoimmunity in the central nervous system.

Amino Acid Sequence↗

PubMed1999

Identification of candidate T-cell epitopes and molecular mimics in chronic Lyme disease.

Elucidating the cellular immune response to infectious agents is a prerequisite for understanding disease pathogenesis and designing effective vaccines. In the identification of microbial T-cell epitopes, the availability of purified or recombinant bacterial proteins has been a chief limiting factor. In chronic infectious diseases such as Lyme disease, immune-mediated damage may add to the effects of direct infection by means of molecular mimicry to tissue autoantigens. Here, we describe a new method to effectively identify both microbial epitopes and candidate autoantigens. The approach combines data acquisition by positional scanning peptide combinatorial libraries and biometric data analysis by generation of scoring matrices. In a patient with chronic neuroborreliosis, we show that this strategy leads to the identification of potentially relevant T-cell targets derived from both Borrelia burgdorferi and the host. We also found that the antigen specificity of a single T-cell clone can be degenerate and yet the clone can preferentially recognize different peptides derived from the same organism, thus demonstrating that flexibility in T-cell recognition does not preclude specificity. This approach has potential applications in the identification of ligands in infectious diseases, tumors and autoimmune diseases.

Adult↗

PubMed1999

Stress doses of hydrocortisone reverse hyperdynamic septic shock: a prospective, randomized, double-blind, single-center study.

OBJECTIVE: To investigate the effects of stress doses of hydrocortisone on the duration of vasopressor therapy in human septic shock. DESIGN: Prospective, randomized, double-blind, single-center study. SETTING: Twenty-bed multidisciplinary intensive care unit in a 1400-bed university hospital. PATIENTS: Forty consecutive patients who met the ACCP/SCCM criteria for septic shock. An additional criterion for inclusion in the study was vasopressor support and high-output circulatory failure with a cardiac index of >4 L/min/m2 after fluid resuscitation (pulmonary capillary wedge pressure: 12-15 mm Hg) and without the use of positive inotropes such as dobutamine or dopexamine. The primary study end point was the time to cessation of vasopressor support (norepinephrine or epinephrine in any dose, dopamine > or = 6 microg/kg/min). Secondary study end points were the evolution of hemodynamics and the multiple organ dysfunction syndrome (MODS). The severity of illness at recruitment was graded using the Acute Physiology and Chronic Health Evaluation II and the Simplified Acute Physiology Score II scoring systems. MODS was described by the Sepsis-related Organ Failure Assessment score. INTERVENTIONS: All eligible patients were prospectively randomized to receive either stress doses of hydrocortisone or placebo. Hydrocortisone was started with a loading dose of 100 mg given within 30 mins and followed by a continuous infusion of 0.18 mg/ kg/hr. When septic shock had been reversed, the dose of hydrocortisone was reduced to 0.08 mg/kg/hr. This dose was kept constant for 6 days. As soon as the underlying infection had been treated successfully or sodium serum concentrations had increased to >155 mmol/L, the hydrocortisone infusion was tapered in steps of 24 mg/day. Physiologic saline solution was the placebo. MEASUREMENTS AND MAIN RESULTS: Hemodynamic and oxygen-derived variables were measured at previously defined time points over a study period of 5 days. Relevant clinical and laboratory measurements were registered for a study period of 14 days to assess the evolution of organ dysfunction. Baseline data at recruitment did not differ between the two groups. Shock reversal was achieved in 18 of the 20 patients treated with hydrocortisone vs. 16 of the 20 patients treated with placebo. Hydrocortisone significantly reduced the time to cessation of vasopressor support. The median time of vasopressor support was 2 days (1st and 3rd Quartiles, 1 and 6 days) in the hydrocortisone-treated group and 7 days (1st and 3rd Quartiles, 3 and 19 days) in the placebo group (p = .005 Breslow test). There was a trend to earlier resolution of the organ dysfunction syndrome in the hydrocortisone group. CONCLUSIONS: Infusion of stress doses of hydrocortisone reduced the time to cessation of vasopressor therapy in human septic shock. This was associated with a trend to earlier resolution of sepsis-induced organ dysfunctions. Overall shock reversal and mortality were not significantly different between the groups in this low-sized single-center study.

Adult↗

PubMed1998

Inhibitors of dipeptidyl peptidase IV/CD26 suppress activation of human MBP-specific CD4+ T cell clones.

The ectoenzyme dipeptidyl peptidase IV (DP IV, EC 3.4.14.5, CD26) has been shown to play a crucial role in T cell activation. Specific inhibitors of DP IV suppress DNA synthesis as well as cytokine production (IL-2, IL-10, IL-12, IFN-gamma) of stimulated human and mouse T cells suggesting a potential application of these effectors in transplantations and autoimmune diseases. In the present study, we have examined the expression of DP IV/CD26 on six myelin basic protein (MBP)(87-99)-specific, CD4+ T cell clones (TCC) derived from patients with multiple sclerosis (MS) as well as the biological effects of the two synthetic DP IV inhibitors Lys[Z(NO2)]-thiazolidide and Lys[Z(NO2)]-pyrrolidide on the function of these cells. All TCC expressed high levels of DP IV/CD26, as shown by flow cytometry and by enzymatic DP IV assay. Enzymatic activity of resting TCC was found to be three to fourfold higher than on resting peripheral blood T cells and close to that of T cells 48 h after PHA stimulation. The DP IV inhibitors suppress DNA synthesis and IFN-gamma, IL-4, and TNF-alpha production of the antigen-stimulated TCC. These data suggest that CD26 plays a role in regulation of activation of autoreactive TCC. Further in-vivo investigations, first in experimental models, will clarify, whether the inhibition of the enzymatic activity of DP IV could be a useful tool for therapeutic interventions in MS or other autoimmune diseases.

CD4 Antigens↗

PubMed1998

Relationships among TCR ligand potency, thresholds for effector function elicitation, and the quality of early signaling events in human T cells.

Determining how receptor ligand quality and quantity together control the biologic responses of T cells is central to understanding normal and pathologic T cell immunity. Here we have carefully examined how variations in antigenic peptide structure and dose affect multiple functional responses of human T cell clones and have correlated these observations with proximal TCR signaling events induced by the same set of related ligands. As the Ag concentration increases, effector functions are elicited according to a clone-specific hierarchy. The absolute amount of each peptide required to stimulate the entire set of effector functions (potency) differs markedly among ligands for a single TCR, correlating with the efficiency of TCR down-modulation and the extent of ZAP-70 activation. However, distinct patterns of TCR zeta-chain phosphorylation were observed, with the ratios of TCRzeta isoforms relating to ligand agonist potency. The appearance of partially phosphorylated TCRzeta isoforms was paralleled by relative changes in certain response thresholds within the hierarchy. Thus, a combination of density, potency, and quality of signaling all contribute to the distinct effects of agonist ligands on T cell immunity.

Cells, Cultured↗

PubMed1998

Predictable TCR antigen recognition based on peptide scans leads to the identification of agonist ligands with no sequence homology.

The potential of CD4+ T cells for cross-recognition of self and foreign Ags has important implications for the understanding of thymic selection, lymphocyte survival, and the occurrence of autoimmune diseases. Here, we define the extensive flexibility of Ag recognition for three human CD4+ autoreactive T cell clones (TCC) by using ligands with single and multiple amino acid (aa) substitutions. Our results demonstrate that the spectrum of tolerated ligands and the resulting stimulatory potency of peptides for a TCC can be predicted by the relative influence of each aa. Using this approach, we have identified stimulatory ligands not sharing a single aa in corresponding positions with the Ag used to establish the TCC. These results argue for an independent contribution of each aa in the peptide sequence to the affinity of the MHC/peptide complex to the TCR.

Amino Acid Sequence↗

PubMed1998

MRI of spinal cord and brain lesions in subacute combined degeneration.

Subacute combined degeneration is a rare cause of demyelination of the dorsal and lateral columns of the spinal cord and even more rarely of the pyramidal and spinocerebellar tracts and cerebellum. We present the initial and follow-up MRI appearances in a patient with subacute combined degeneration of the spinal cord, brain stem and cerebellum, due to vitamin B12 deficiency. The lesions in these structures were demonstrated clearly as pathologically high-signal areas on T2-weighted images. These lesions, except those of the brain stem and cerebellum, disappeared 4 months after therapy. MRI 14 months after the patient's discharge on vitamin B12 therapy showed the same picture.

Brain Stem↗

PubMed1998

Probing degeneracy in T-cell recognition using peptide combinatorial libraries.

Recent studies have demonstrated flexibility of the T-cell receptor (TCR) with respect to recognition of peptide bound to self major histocompatibility complex (MHC). With the introduction of peptide combinatorial libraries, it has become possible to dissect the extent of degeneracy in T-cell recognition. On the basis of these novel findings, Bernhard Hemmer and colleagues propose a conceptual framework for lymphocyte selection and survival and the occurrence of autoimmunity.

Humans↗

PubMed1998

The use of soluble synthetic peptide combinatorial libraries to determine antigen recognition of T cells.

T cells identify by their T-cell receptor (TCR) short peptides in the context of major histocompatibility complex (MHC) molecules. The interaction of the trimolecular complex composed of the TCR and MHC bound peptide was extensively studied using substitution analogs of the original peptide ligands to define those residues important for T-cell recognition in the peptide chain. This approach has led to the observation that T-cell recognition is highly flexible and that many different peptides can be recognized by an individual TCR. Others and we have recently introduced synthetic peptide combinatorial libraries (SCL) to investigate T-cell recognition. Here we review the SCL-based approaches and describe our current techniques for mapping TCR motifs for CD4+ T cells. The implications of our findings for the understanding of T-cell recognition, as well as for future applications to study T-cell responses in infectious diseases, autoimmune disorders and cancer are discussed.

Amino Acid Sequence↗

PubMed1998

Subacute combined degeneration: clinical, electrophysiological, and magnetic resonance imaging findings.

OBJECTIVE: Vitamin B12 deficiency is a systemic disease that often affects the nervous system. One of the most prevalent manifestations is subacute combined degeneration (SCD) of the spinal cord. To access the clinical, electrophysiological, and structural abnormalities associated with SCD, a study was conducted in nine patients. METHODS: Clinical, electrophysiological (electroneurography, somatosensory and motor evoked potentials), and MRI evaluations were performed in patients before and after treatment. RESULTS: The most prominent clinical and electrophysiological findings in all patients were dysfunctions of the posterior column. Corresponding hyperintense lesions in the posterior column of the spinal cord were found in two patients by T2 weighted MRI. Damage to the central motor pathway was identified in four patients. Demyelinating neuropathy was present in one patient and axonal neuropathy in four. All patients showed improvement of their symptoms after treatment with cobalamin. Abnormalities of the spinal cord on MRI disappeared early in recovery. Motor evoked potentials and median somatosensory evoked potentials typically normalised after treatment, whereas tibial somatosensory evoked potentials remained abnormal in most patients. CONCLUSIONS: Clinical, electrophysiological, and MRI findings associated with SCD in vitamin B12 deficiency are diverse. Thus vitamin B12 deficiency should be considered in the differential diagnosis of all spinal cord, peripheral nerve, and neuropsychiatric disorders.

Acute Disease↗

PubMed1997

Differential expression of cyclic nucleotide phosphodiesterase 3 and 4 activities in human T cell clones specific for myelin basic protein.

Little is known concerning the relative distribution and function of the different cyclic nucleotide phosphodiesterases (PDEs) in lymphocytes. Recent reports, however, have indicated that specific PDE4 inhibitors were effective in treatment of experimental allergic encephalomyelitis, an animal model of multiple sclerosis. The therapeutic effect of PDE4 inhibitors is thought to be related to inhibition of autoreactive CD4+ T cells specific for myelin basic protein (MBP) or other myelin proteins. Human autoreactive CD4+ T lymphocyte clones (TCC), specific for the immunodominant MBP epitope (amino acids 83-99), contain PDE3 and PDE4, two PDEs that exhibit a high affinity for cAMP. Amplification of TCC mRNA by reverse transcription-PCR indicated that TCC PDE3 mRNA was of the PDE3B, not PDE3A, subtype. Different TCC contained different proportions of PDE3 and PDE4, and their activities increased during Ag (MBP) stimulation. Specific PDE3 (cilostamide) and PDE4 (rolipram) inhibitors suppressed [3H]thymidine incorporation in TCC. Since it is believed that many autoimmune diseases are at least partially mediated by autoreactive CD4+ T cells, these observations may have important implications not only for the treatment of multiple sclerosis but also for other autoimmune diseases.

3',5'-Cyclic-AMP Phosphodiesterases↗