Immunosuppressive treatment of ocular myasthenia gravis

Myasthenia gravis (MG) is caused by autoantibodies against proteins at the neuromuscular junction. This autoimmune process leads to abnormal fatiguability and weakness of striated muscle. Ptosis and diplopia are among the most common manifestations of MG. The term "ocular MG" (OMG) as opposed to "generalised MG" (GMG) is used to define the clinical subtype of MG with isolated eye muscle weakness. Although OMG may appear to cause only moderate disability, it can significantly impair the patient's activities of daily living and progress to generalised myasthenia. Therefore, a clear management plan should be installed early in these patients. Since prospective treatment trials have not been performed, basic management strategies for OMG have to be deduced from retrospective studies, trials in GMG, and generally accepted clinical experience. Cholinesterase inhibitors are used in all types of MG, but are often less helpful in OMG. In the absence of thymoma, thymectomy is usually not considered in OMG, although a few studies have described histological abnormalities in thymuses from patients with OMG. Corticosteroids are of great short term benefit in most patients with OMG but potential adverse effects limit their long term use. Azathioprine is needed to reduce long term corticosteroid adverse effects, but this agent requires about 6 months to be effective. In summary, OMG has a good prognosis in most patients, with corticosteroids and azathioprine being the major treatment options. The challenges for the clinician are to recognise the condition despite the large number of differential diagnoses, to minimise the patient's symptoms using the therapies available and to carefully limit potentially hazardous therapeutic efforts, especially in mild or even uncertain cases.

No association of three polymorphisms in the alpha-2-macroglobulin and lipoprotein related receptor genes with multiple sclerosis

Alpha-2-macroglobulin (A2M) is a proteinase inhibitor involved in deactivation of cytokines and modulation of antigen-mediated immune responses. Based on its role in inflammatory and neurodegenerative disorders, we investigated the role of A2M and its receptor low-density lipoprotein receptor-related protein (LRP) for the development of multiple sclerosis (MS). We analyzed the frequency of two polymorphisms in the A2M (Val 1000 Ile, Exon 18 del), and one polymorphism in the LRP (A216V) gene in a case control study involving 326 MS patients, and 290 controls, all defined for the expression of HLA-DR15. No association was found for any of the three polymorphism with MS. Furthermore, no differences in serum A2M levels were detected between MS patients and controls. The results do not suggest a contribution of A2M and LRP to the development of MS.

Combinatorial peptide libraries and biometric score matrices permit the quantitative analysis of specific and degenerate interactions between clonotypic TCR and MHC peptide ligands

The interaction of TCRs with MHC peptide ligands can be highly flexible, so that many different peptides are recognized by the same TCR in the context of a single restriction element. We provide a quantitative description of such interactions, which allows the identification of T cell epitopes and molecular mimics. The response of T cell clones to positional scanning synthetic combinatorial libraries is analyzed with a mathematical approach that is based on a model of independent contribution of individual amino acids to peptide Ag recognition. This biometric analysis compares the information derived from these libraries composed of trillions of decapeptides with all the millions of decapeptides contained in a protein database to rank and predict the most stimulatory peptides for a given T cell clone. We demonstrate the predictive power of the novel strategy and show that, together with gene expression profiling by cDNA microarrays, it leads to the identification of novel candidate autoantigens in the inflammatory autoimmune disease, multiple sclerosis.

New approaches to dissect degeneracy and specificity in T cell antigen recognition

The acquired immune system is a complex and very effective defense against invading pathogens such as bacteria and viruses. T cells are central to the acquired immune system by controlling B and T cell activation and induction of T cell effector functions. The key event for T cell activation is the recognition of a specific antigen by the T cell receptor. During the past decade antigen recognition of T cells has been investigated intensively leading to new insights into the molecular mechanisms of T cell activation. In addition to the resolution of the molecular structure of the trimolecular complex (T cell receptor, peptide, major histocompatibility complex) functional studies have demonstrated the flexibility of the T cell receptor interaction with its ligand. These observations have had strong implications for the understanding of T cell selection, maturation, and repertoire maintenance. In addition, the flexibility of the T cell receptor has provided the basis for novel methods to dissect antigen recognition and define the repertoire of ligands for a given receptor. Here, we summarize recent progress on T cell recognition and method innovations with respect to future studies in autoimmune diseases.

Molecular mimicry and antigen-specific T cell responses in multiple sclerosis and chronic CNS Lyme disease

The concept of molecular mimicry provides and elegant framework as to how cross-reactivity between antigens from a foreign agent with self proteins may trigger autoimmune diseases. While it was previously thought that sequence and structural homology between foreign and self proteins or the sharing of T cell receptor (TCR) and MHC-binding motifs are required for molecular mimicry to occur, we have shown that even completely unrelated peptide sequences may lead to cross-recognition by T cells. The use of synthetic combinatorial peptide libraries in the positional scanning format (PS-SCL) together with novel biometric prediction approaches has allowed us to describe the recognition profiles of individual autoreactive T cell clones (TCC) with unprecedented accuracy. Through studies of myelin-specific TCC as well as clones from the nervous system of patients suffering from chronic central nervous (CNS) Lyme disease it has become clear that at least some T cells are more degenerate than previously anticipated. These data will not only help us to redefine what constitutes specific T cell recognition, but also allow us to study in more detail the biological role of molecular mimicry. A recent clinical trial with an altered peptide ligand (APL) of one of the candidate myelin basic protein (MBP) epitopes in MS (amino acids 83-99) has shown that such a modified MBP peptide may not only have therapeutic efficacy, but also bears the potential to exacerbate disease. Thus, we provide firm evidence that the basic principles of cross-recognition and their pathogenetic significance are relevant in MS.

Rapid identification of local T cell expansion in inflammatory organ diseases by flow cytometric T cell receptor Vbeta analysis

Oligoclonal expansion of antigen-specific T cells occurs frequently during inflammatory diseases. These cells may persist for a long time at high frequency in the body and be enriched in the affected tissues. As a screening test for expanded cell T cell populations at sites of inflammation, we developed an optimized methodology for flow-cytometry-based quantification of T cell receptor Vbeta (TCRBV) expression. We first validated the specificity of a TCRBV-specific monoclonal antibody set by direct comparison with PCR-based analysis of mono- and polyclonal T cell samples. This monoclonal antibody (mAb) panel recognized approximately two thirds of the T cell receptor alpha/beta repertoire in a group of 64 healthy donors and allowed defining TCR usage in the CD4+ and CD8+ subsets. The reliable detection of expanded Vbeta gene families in T cell populations was confirmed in experiments on superantigen-stimulated T cells. Through differential TCR analysis on T cell subpopulations in cerebrospinal fluid and blood in patients with acute encephalitis, we were able to identify locally expanded CD8+ T cells. The power of this approach affords not only high-throughput comparative TCR analysis for immunological studies in vitro, but also rapid ex vivo identification of cell populations enriched in organ compartments during inflammatory diseases.

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.

Degeneracy in T-cell antigen recognition - implications for the pathogenesis of autoimmune diseases

T-cells recognize by their T-cell receptor (TCR) short peptides presented by major histocompatibility complex (MHC) molecules. Based on functional and structural data, it has become widely accepted that this interaction is highly flexible thus allowing a specific TCR to interact with a broad range of different peptide ligands. Although cross-reactivity is essential for selection and maintenance of the T-cell repertoire, it also carries the danger of inducing autoreactivity following protective immune responses. This hypothesis has been supported by a large number of findings in vitro and in vivo experimental systems. Here we discuss recent findings on cross-recognition of T-cells and provide a new experimental approach to address specificity and cross-reactivity in autoimmune disorders.

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.

Contribution of individual amino acids within MHC molecule or antigenic peptide to TCR ligand potency

The TCR recognition of peptides bound to MHC class II molecules is highly flexible in some T cells. Although progress has been made in understanding the interactions within the trimolecular complex, to what extent the individual components and their amino acid composition contribute to ligand recognition by individual T cells is not completely understood. We investigated how single amino acid residues influence Ag recognition of T cells by combining several experimental approaches. We defined TCR motifs for CD4+ T cells using peptide synthetic combinatorial libraries in the positional scanning format (PS-SCL) and single amino acid-modified peptide analogues. The similarity of the TCR motifs defined by both methods and the identification of stimulatory antigenic peptides by the PS-SCL approach argue for a contribution of each amino acid residue to the overall potency of the antigenic peptide ligand. In some instances, however, motifs are formed by adjacent amino acids, and their combined influence is superimposed on the overall contribution of each amino acid within the peptide epitope. In contrast to the flexibility of the TCR to interact with different peptides, recognition was very sensitive toward modifications of the MHC-restriction element. Exchanges of just one amino acid of the MHC molecule drastically reduced the number of peptides recognized. The results indicate that a specific MHC molecule not only selects certain peptides, but also is crucial for setting an affinity threshold for TCR recognition, which determines the flexibility in peptide recognition for a given TCR.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

Human T-cell response to myelin basic protein peptide (83-99): extensive heterogeneity in antigen recognition, function, and phenotype

Multiple sclerosis (MS) is considered a T cell-mediated autoimmune disease, and myelin proteins are the most likely candidate autoantigens. Based on experiments performed in experimental allergic encephalomyelitis (EAE), innovative immunotherapies have been developed that target either the specific trimolecular complex of encephalitogenic T cells, consisting of T-cell receptor (TCR), major histocompatibility complex (MHC; HLA in humans) class II molecule, and autoantigenic peptide, or the effector functions of these cells. To provide the basis for the transfer of these specific immunotherapies to MS, we extensively characterized the human T-cell response to one major myelin epitope, the myelin basic protein peptide (83-99). We analyzed restriction element, TCR usage and affinity, fine specificity, cytokine production, cytolytic activity, and expression of surface molecules on 41 T-cell clones (TCCs) derived from MS patients and normal controls. We demonstrate a high degree of complexity of recognition patterns as well as of functional phenotypes among T cells responding to the same epitope. In contrast to results from animal models, these findings indicate that the design of epitope-based specific immunotherapies for MS is more difficult than previously thought.

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.

T cell response to myelin basic protein in the context of the multiple sclerosis-associated HLA-DR15 haplotype: peptide binding, immunodominance and effector functions of T cells

In this study, we evaluated the role of the two functional HLA-DR heterodimers, DR2a (DR alpha paired with the beta chain encoded by DRB5*0101) and DR2b (DR alpha paired with the beta chain encoded by DRB1*1501), that are coexpressed in the multiple sclerosis (MS)-associated haplotype HLA-DR15 Dw2, in presenting myelin basic protein (MBP) peptides to MBP-specific T cell lines (TCL). Our results show that both HLA-DR molecules serve as restriction elements for HLA-DR15-restricted TCL. Slightly higher numbers of TCL use DR2a as restriction element, and the epitopes contained in the immunodominant C-terminal region (131-159) are uniquely restricted by DR2a. The immunodominant middle epitope (81-99) is recognized in the context of both DR2a and DR2b, but this specificity strongly dominates the DR2b-restricted T cell response. Overall, immunodominance in the MBP-specific T cell response correlated well with peptide binding to DR2a or DR2b, demonstrating that the affinity of MHC-peptide interactions is important for shaping the T cell response to this autoantigen. Furthermore, we show that binding of the middle MBP peptide to HLA-DR15 molecules prevents cleavage by cathepsin D, a protease abundantly found in endosomal processing compartments, and thus contributes to its immunodominance. Surprisingly, the restriction element employed by MBP-specific T cell clones influenced the effector function (i.e., cytotoxic activity) of T cells irrespective of their peptide fine specificity.

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.

Identification of high potency microbial and self ligands for a human autoreactive class II-restricted T cell clone

CD4+ class II-restricted T cells specific for self antigens are thought to be involved in the pathogenesis of most human autoimmune diseases and molecular mimicry between foreign and self ligands has been implicated as a possible mechanism for their activation. In this report we introduce combinatorial peptide libraries as a powerful tool to identify cross-reactive ligands for these T cells. The antigen recognition of a CD4+ T cell clone (TCC) specific for myelin basic protein peptide (MBP) (86-96) was dissected by the response to a set of 220 11-mer peptide sublibraries. Based on the results obtained with the libraries for each position of the antigen, artificial peptides were found that induced proliferative responses at much lower concentrations than MBP(86-96). In addition stimulatory ligands derived from protein sequences of self and microbial proteins were identified, some of them even more potent agonists than MBP(86-96). These results indicate that: (a) for at least some autoreactive CD4+ T cells antigen recognition is highly degenerate; (b) the autoantigen used to establish the TCC represents only a suboptimal ligand for the TCC; (c) a completely random and unbiased approach such as combinatorial peptide libraries can decrypt the spectrum of stimulatory ligands for a T cell receptor (TCR).

Modifications of peptide ligands enhancing T cell responsiveness imply large numbers of stimulatory ligands for autoreactive T cells

In this report, we demonstrate for autoreactive T cell clones that single amino acid modifications of the antigenic ligand can result in not only abrogated, decreased, or unmodified, but also increased, T cell responsiveness (superagonist ligands). We further studied the effects of combinations of multiple substitutions with different effects in single peptides. Experiments with peptides carrying multiple amino acid exchanges revealed that the final outcome of TCR ligation by a given ligand is the integration of negative, neutral, and positive effects of each single residue. In addition, the introduction of superagonist substitutions together with nonconservative modifications of primary and secondary TCR contacts resulted in stimulatory ligands. These findings indicate that: 1) the specificity of a single TCR is highly degenerate; 2) ligands exist for autoreactive T cells that have higher agonist activity than the autoantigen itself; 3) the rules to search for cross-reactive epitopes in autoimmunity should take into account that amino acids at certain positions within an antigenic peptide may exert superagonist activity and compensate for the negative effects of residues at other positions that would otherwise not be tolerated.

Modifications of peptide ligands enhancing T cell responsiveness imply large numbers of stimulatory ligands for autoreactive T cells

In this report, we demonstrate for autoreactive T cell clones that single amino acid modifications of the antigenic ligand can result in not only abrogated, decreased, or unmodified, but also increased, T cell responsiveness (superagonist ligands). We further studied the effects of combinations of multiple substitutions with different effects in single peptides. Experiments with peptides carrying multiple amino acid exchanges revealed that the final outcome of TCR ligation by a given ligand is the integration of negative, neutral, and positive effects of each single residue. In addition, the introduction of superagonist substitutions together with nonconservative modifications of primary and secondary TCR contacts resulted in stimulatory ligands. These findings indicate that: 1) the specificity of a single TCR is highly degenerate; 2) ligands exist for autoreactive T cells that have higher agonist activity than the autoantigen itself; 3) the rules to search for cross-reactive epitopes in autoimmunity should take into account that amino acids at certain positions within an antigenic peptide may exert superagonist activity and compensate for the negative effects of residues at other positions that would otherwise not be tolerated.

Human autoreactive CD4+ T cell clones use perforin- or Fas/Fas ligand-mediated pathways for target cell lysis

It is well established that target cell lysis by MHC class I-restricted CD8+ T cells is an important defense mechanism during infections with intracellular pathogens or against tumor targets. On the other hand, little is known about the physiologic role and the mechanisms of cytotoxicity of CD4+ MHC class II-restricted T cells. We have recently demonstrated that human autoreactive CD4+ T cells specific for one candidate autoantigen of multiple sclerosis, myelin basic protein, can mediate cytotoxicity. In the present report, we analyze the cytolytic mechanisms employed by these cells. We show that individual T cell clones, regardless of their cytokine phenotype, can be noncytotoxic or lyse target cells via either perforin- or Fas/Fas ligand-mediated cytotoxicity.

Human autoreactive CD4+ T cell clones use perforin- or Fas/Fas ligand-mediated pathways for target cell lysis

It is well established that target cell lysis by MHC class I-restricted CD8+ T cells is an important defense mechanism during infections with intracellular pathogens or against tumor targets. On the other hand, little is known about the physiologic role and the mechanisms of cytotoxicity of CD4+ MHC class II-restricted T cells. We have recently demonstrated that human autoreactive CD4+ T cells specific for one candidate autoantigen of multiple sclerosis, myelin basic protein, can mediate cytotoxicity. In the present report, we analyze the cytolytic mechanisms employed by these cells. We show that individual T cell clones, regardless of their cytokine phenotype, can be noncytotoxic or lyse target cells via either perforin- or Fas/Fas ligand-mediated cytotoxicity.

Differential activation of human autoreactive T cell clones by altered peptide ligands derived from myelin basic protein peptide (87-99)

We have examined the functional consequences induced by interaction of DR2a-restricted myelin basic protein (MBP) (87-99)-specific T cell clones (TCC) with altered peptide ligands (APL) derived from MBP peptide (87-99). The immunodominant MBP peptide (87-99) has been implicated as a candidate antigen in multiple sclerosis (MS) by several lines of evidence. In the present study, we have defined the T cell receptor (TCR) contact residues for DR2a-restricted, (87-99)-specific T helper type 1 T cells to design APL suitable to modify the functions of such T cells potentially relevant for the pathogenesis of MS. We show that neutral (L-alanine substitutions) or conservative exchanges of the primary and secondary TCR contact residues lead to various alterations of T cell function, ranging from differences in interleukin-2 receptor up-regulation to anergy induction and TCR antagonism. The potential usefulness of APL as an immunomodulating therapy for DR2+ MS patients is discussed.

Cytokine phenotype of human autoreactive T cell clones specific for the immunodominant myelin basic protein peptide (83-99)

Experimental allergic encephalomyelitis (EAE), an animal model resembling multiple sclerosis (MS), is mediated by myelin antigen-specific CD4+ T cells secreting cytokines such as interferon-gamma (IFN-gamma), tumor necrosis factor-beta (TNF-beta), and the proinflammatory cytokine TNF-alpha-all associated with the T-helper-1 (Th1) T cell subset. Based on numerous similarities between MS and EAE, it has been postulated that Th1-like T cells are involved in the pathogenesis of MS. Production of proinflammatory cytokines such as IFN-gamma and, in particular, TNF-alpha/beta by autoreactive T cells is considered crucial for the initiation and amplification of inflammatory brain lesions and possibly also for direct myelin damage. In contrast, regulatory cytokines such as interleukin-4 (IL-4), IL-10, and IL-13, which are associated with the Th2-like phenotype, may play a role in the resolution of relapses. Although the human T cell response to myelin basic protein (MBP) is well characterized in terms of antigen specificity, HLA restriction, and T cell-receptor (TCR) usage, little is known about the cytokine pattern of these autoreactive T cells. To gain such information, conditions for studying cytokine secretion by human autoreactive T cell clones (TCC) were established. The cytokine secretion profile of human autoreactive CD4+ TCC, specific for myelin basic protein peptide (83-89) [MBP(83-99)], a candidate autoantigen in MS, was investigated. Our results show that TCC cytokine production in long-term culture was stable. In addition, the correlation of various cytokines within specific TCC revealed differences compared to murine T cells. The comparison of 30 human MBP (83-99)-specific TCC demonstrated heterogeneity in cytokine secretion, with a continuum between Th1- and Th2-like cells rather than distinct Th1 or Th2 subsets. These data are important for further investigation of the potential role of cytokines in the inflammatory process of MS, and provide a powerful tool to investigate therapeutic interventions with respect to their influence on cytokine secretion of autoreactive T cells.

Human T lymphocytes specific for the immunodominant 83-99 epitope of myelin basic protein: recognition of golli MBP HOG 7

Myelin basic protein (MBP) is a candidate autoantigen in the disease multiple sclerosis. Although MBP was thought to be sequestered behind the blood-brain barrier, isoforms of MBPs have recently been demonstrated in lymphoid tissues. These isoforms, termed golli MBPs, contain sequences that are shared with "classic" MBP within the CNS. In the present study, we have determined that epitopes within golli MBP isoforms may be recognized by human T lymphocyte clones specific for classic MBP. Ten of 12 T-cell clones recognized golli MBP. Although 11 clones were specific for the immunodominant 83-99 sequence, the clones differed with respect to human leukocyte antigen (HLA) restriction, T-helper phenotype, cytolytic activity, and T-cell receptor usage. Greater responses to classic MBP than to golli MBP suggested a difference in the ability of the two proteins to be processed and to present epitopes therein. These data advance the hypothesis that golli MBP sequences expressed within lymphoid tissues may be recognized by classic MBP-specific T lymphocytes during central or peripheral tolerance.

[A case of gustatory sweating and facial pain]

We report a case of a patient with gustatory sweating, a unilateral hyperhidrosis following a gustatory stimulus and an accompanying thermoregulatory hypohidrosis in the same area. Unusual features in this case are a possible association with a face pain and that the causing lesion can be localized in the brain-stem by neurological-topical reasoning. Most cases of gustatory sweating are caused by damage to the parotid gland.

Heart rate and ventilation in relation to venous [K+], osmolality, pH, PCO2, PO2, [orthophosphate], and [lactate] at transition from rest to exercise in athletes and non-athletes

To evaluate to what metabolci event in contracting muscles heart rate (HR) and VE are related, time courses of femoral and cubital venous [K=], osomolality (OSM), pH, POC2, PO2, [lactate], and [orthophosphate] ([Pi]) at onset of exercise were studied in athletes (TR) and non-athletes (UT) and compared to time courses of HR and VE. During ischaemic work with the calf muscles it could be shown that most of these blood constituents were only released from contracting muscles. Thus their time courses reflected the metabolic events in working muscles being not essentially disturbed by non-working parts of the body. Ischaemic work induced, however, substantial increases of HR and VE. In the course of non-ischaemic bicycle work HR and VE rose more rapidly in TR than in UT but were lower in TR during the steady state. During non-ischaemic work only the increased of femoral venous [K=1 closely mimicked the cardiorespiratory transients in TR as well as in UT. None of the other femoral venous substances showed such a rapid change or such typical variations between TR and UT. Cubital venous [K=1 and [Pi] approached femoral venous concentrations only in second minute after start whereas pH, PCO2, and OSM increased mainly in venous outflow from contracting muscles. PO2 decreased in femoral venous blood of TR and UT, but in cubital venous blood it remained depressed only in UT. It was discussed that the cardiorespiratory adjustment during the initial stages of work was related to K+ release in working muscles and not to O2 consuming or H+ producing processes, nor to release of Pi or increase of OSM.

Relationships of femoral venous [K+], PO2, osmolality, and [orthophosphate) with heart rate, ventilation, and leg blood flow during bicycle exercise in athletes and non-athletes

The relationship of femoral venous [K+], [H+], osmolality (OSM), PO2, and [inorganic phosphate] ([Pi]) with heart rate (HR), ventilation (VE), and calculated leg blood flow (Q) were investigated during bicycle exercise in endurance trained (TR) and untrained (UT) test subjects. At a given VO2 the increases of [K+], OSM, [Pi] and the decrease of PO2 were significantly lower in TR than in UT. In the same proportion the increases of HR, VE, and Q were diminished. Thus in TR and UT identical and highly significantly correlated regression lines of [K+], [H+], OSM, [Pi] and PO2 with HR, VE, and Q were obtained. These constituents changed in the same proportion as the relative VO2 in TR and UT. No relationships with [Na+], [Ca++], and [ Mg++] were found. By means of a multiple regression analysis the partial influence of K+, H+, OSM, PO2, and Pi upon the total change of HR, VE and Q was estimated to compare with data from infusion experiments. The findings were discussed in view of the hypothesis that these candidates may provide linkage between metabolic events, circulatory, and ventilatory adjustments during work.

Effects of a multi-hour immersion with intermittent exercise on urinary excretion and tilt table tolerance in athletes and nonathletes

The circulatory and diuretic responses of athletes and non-athletes to 6-h water i-mersion with intermittent swimming exercise (series I) as well as to 8-h inactive immersions (series II) were studied. With simultaneous intermittent exercise, the normally arising diuresis during a water bath was strongly suppressed in athletes and even abolished in nonathletes. In subsequent tilt table tests, 3 of 11 (27.3%) athletes of series I and 3 of 4 (75%) of series II collapsed, whereas all nonathletes tolerated the vertical position without any subjective complaints. By use of the so-called "orthostatic index" (4) the later group, however, was also shown to yield a substantially better orthostatic stability in series I than in series II. The protective effect of intermittent physical activity for simulation of the weightless state can possibly be explained by assuming a less-reduced plasma volume via a diminished urinary excretion.

Influences of exercise and endurance training on the oxygen dissociation curve of blood under in vivo and in vitro conditions

In experiments with graded exercise of 15 men (6 untrained, 3 semitrained, 6 endurance-trained) the trained subjects showed a massive shift to the right of the in vivo O2 dissociation curve (ODC) of femoral venous blood. At a saturation of 20 to 25% (18 mkp/sec) Po2 was about 9 mm Hg higher for the trained than for the untrained group. The following factors play a role: 1. The 2,3-diphosphoglycerate [2,3-DPG] concentration was increased by 15 to 20% in the trained group which explains about 2 mm Hg of the diffenence in Po2-2. Exercise acidosis in the femoral venous blood depends to a large extent on CO2 in the trained, but on lactic acid in the untrained group. At low saturations the CO2-Bohr effect increases sharply thus having a greater importance in the trained subjects. This factor can explain about 2 mm Hg of the difference. However, influence of chloride and 2,3-DPG on the Bohr effect must be taken into consideration. 3. Since the large ODC-shift to the right of the trained group was not reproducible under in vitro conditions, it is suggested that a rapidly decaying unknown substance accounts for the remaining difference in Po2.