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Biomedical subjects

Michael K Racke

Publications and source records attributed to Michael K Racke.

At least 19 recordsLinked to original sources
PubMed2006

Glatiramer acetate (GA) therapy induces a focused, oligoclonal CD8+ T-cell repertoire in multiple sclerosis.

We have demonstrated that GA therapy induces a differential upregulation of GA-specific, cytotoxic/suppressor CD8+ T-cell responses in MS patients. We utilized a novel combination of flow sorting and anchored PCR to analyze the evolving clonal composition of GA-specific CD4+ and CD8+ T-cells. TCRbeta chain analysis revealed the development of an oligoclonal GA-specific CD8+ repertoire with persistence of dominant clones over long periods. Interestingly, some sequences resembled published oligoclonal CD8+ TCR sequences from MS lesions. In contrast, GA-specific CD4+ responses were polyclonal and showed continual evolution of their repertoire. This clonotypic and functional analysis provides mechanistic insights into GA therapy.

Adult↗
PubMed2006

Phenotypic characterization of autoreactive T cells in multiple sclerosis.

MS has been hypothesized to result from autoreactive T cell responses against myelin antigens. In this report, we examined myelin-specific CD8 and CD4 T cells for two markers differentially expressed on naïve, memory and chronically stimulated T cells, CD28 and CD57. We observed differential expression on CD8 T cells in response to myelin antigens, but not in response to the recall antigen mumps. We demonstrate these cells display reduced proliferation and this may explain why therapies that limit the proliferation of T cells have had little effect on the course of MS, particularly later in the course of the disease.

Adult↗
PubMed2006

CD28-CD57+ T cells predominate in CD8 responses to glatiramer acetate.

Human T cells adopt a CD28-CD57+ phenotype in chronic viral infections and this has been hypothesized to result from continuous stimulation, however this phenotype may be due to direct viral effects on T cells. Employing MS patients before and after chronic in vivo administration of the antigen glatiramer acetate (GA) we examine this hypothesis. Pre-treatment glatiramer acetate-specific CD8 T cells were CD57-Perforin-. This changed to a predominantly CD28-CD57+Perforin+ response after administration of this drug. This phenotype was only observed after chronic stimulation and not in a recall response to mumps. The relevance to GA's mechanism of action is discussed.

Adult↗
PubMed2006

Peroxisome proliferator-activated receptor-alpha and retinoid X receptor agonists inhibit inflammatory responses of astrocytes.

The peroxisome proliferator-activated receptor-alpha (PPAR-alpha) plays a key role in lipid metabolism and inflammation. Recently, we demonstrated that administration of the PPAR-alpha agonists gemfibrozil and fenofibrate, inhibit the clinical signs of experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis (MS). In the present study, we investigated the effects of PPAR-alpha agonists on primary mouse astrocytes, a cell type implicated in the pathology of MS and EAE. Our studies demonstrated that the PPAR-alpha agonists fenofibrate, and WY 14643 inhibited NO production by LPS-stimulated astrocytes in a dose-dependent manner. Additionally, PPAR-alpha agonists inhibited the secretion of the pro-inflammatory cytokines TNF-alpha, IL-1beta, and IL-6 by LPS-stimulated astrocytes. Fenofibrate inhibited NF-kappaB DNA binding activity, suggesting a mechanism by which PPAR-alpha agonists may regulate the expression of genes encoding these pro-inflammatory molecules. Retinoid X receptors (RXRs) physically interact with PPAR-alpha receptors, and the resulting heterodimers regulate the expression of PPAR-responsive genes. Interestingly, a combination of 9-cis RA and the PPAR-alpha agonists fenofibrate or gemfibrozil cooperatively inhibited NO, TNF-alpha, IL-1beta, IL-6, and MCP-1 production by these cells. Collectively, these results raise the possibility that PPAR-alpha and RXR agonists might be effective in the treatment of MS, where activated astrocytes are believed to contribute to disease pathology.

Animals↗
PubMed2006

Peroxisome proliferator-activated receptor agonist regulation of glial activation: relevance to CNS inflammatory disorders.

Peroxisome proliferator-activated receptors (PPARs) play key roles in lipid metabolism and inflammation. Recent studies indicated that PPARs are also capable of modulating immune responses. Microglia and astrocytes are cells resident to the central nervous system (CNS) that function to protect against environmental insults including pathogens. However, following CNS inflammation, reactive gliosis occurs which is characterized by astrocyte hypertrophy and increased glial proliferation. Under such conditions, glia can become chronically activated and may contribute to the neuropathology associated with a variety of neuroinflammatory disorders including multiple sclerosis (MS), Alzheimer's disease (AD), Parkinson's disease (PD), amyotrophic lateral sclerosis (ALS), and stroke. A review of the role of PPAR agonists in modulating glial cell activation is presented. Included is a discussion of the molecular mechanisms of action of these PPAR agonists and the potential utility of these agents for the treatment of neuroinflammatory disorders.

Animals↗
PubMed2006

Therapeutic induction of regulatory, cytotoxic CD8+ T cells in multiple sclerosis.

In the setting of autoimmunity, one of the goals of successful therapeutic immune modulation is the induction of peripheral tolerance, a large part of which is mediated by regulatory/suppressor T cells. In this report, we demonstrate a novel immunomodulatory mechanism by an FDA-approved, exogenous peptide-based therapy that incites an HLA class I-restricted, cytotoxic suppressor CD8+ T cell response. We have shown previously that treatment of multiple sclerosis (MS) with glatiramer acetate (GA; Copaxone) induces differential up-regulation of GA-reactive CD8+ T cell responses. We now show that these GA-induced CD8+ T cells are regulatory/suppressor in nature. Untreated patients show overall deficit in CD8+ T cell-mediated suppression, compared with healthy subjects. GA therapy significantly enhances this suppressive ability, which is mediated by cell contact-dependent mechanisms. CD8+ T cells from GA-treated patients and healthy subjects, but not those from untreated patients with MS, exhibit potent, HLA class I-restricted, GA-specific cytotoxicity. We further show that these GA-induced cytotoxic CD8+ T cells can directly kill CD4+ T cells in a GA-specific manner. Killing is enhanced by preactivation of target CD4+ T cells and may depend on presentation of GA through HLA-E. Thus, we demonstrate that GA therapy induces a suppressor/cytotoxic CD8+ T cell response, which is capable of modulating in vivo immune responses during ongoing therapy. These studies not only explain several prior observations relating to the mechanism of this drug but also provide important insights into the natural immune interplay underlying this human immune-mediated disease.

Adult↗
PubMed2006

Altered CD4+/CD8+ T-cell ratios in cerebrospinal fluid of natalizumab-treated patients with multiple sclerosis.

BACKGROUND: Treatment with natalizumab, a monoclonal antibody against the adhesion molecule very late activation antigen 4, an alpha4beta(1) integrin, was recently associated with the development of progressive multifocal leukoencephalopathy, a demyelinating disorder of the central nervous system caused by JC virus infection. OBJECTIVE: To test the effect of natalizumab treatment on the CD4(+)/CD8(+) T-cell ratios in cerebrospinal fluid (CSF) and peripheral blood. DESIGN: Prospective longitudinal study. SETTING: Academic and private multiple sclerosis centers. PATIENTS: Patients with multiple sclerosis (MS) treated with natalizumab, untreated patients with MS, patients with other neurologic diseases, and human immunodeficiency virus-infected patients. MAIN OUTCOME MEASURES: CD4(+) and CD8(+) T cells were enumerated in CSF and peripheral blood. The mean fluorescence intensity of unbound alpha4 integrin on peripheral blood CD4(+) and CD8(+) T cells was analyzed before and after natalizumab therapy. RESULTS: Natalizumab therapy decreased the CSF CD4(+)/CD8(+) ratio of patients with MS to levels similar to those of human immunodeficiency virus-infected patients. CD4(+)/CD8(+) ratios in peripheral blood in patients with MS progressively decreased with the number of natalizumab doses, but they remained within normal limits. Six months after the cessation of natalizumab therapy, CSF CD4(+)/CD8(+) ratios normalized. The expression of unbound alpha4 integrin on peripheral blood T cells decreases with natalizumab therapy and was significantly lower on CD4(+) vs CD8(+) T cells. CONCLUSIONS: Natalizumab treatment alters the CSF CD4(+)/CD8(+) ratio. Lower expression of unbound alpha4 integrin on CD4(+) T cells is one possible mechanism. These results may have implications for the observation that some natalizumab-treated patients with MS developed progressive multifocal leukoencephalopathy.

Adolescent↗
PubMed2006

Immune surveillance in multiple sclerosis patients treated with natalizumab.

OBJECTIVE: Our objective was to test whether natalizumab, an antibody against very late activating antigen (VLA)-4, interferes with central nervous system immune surveillance as assessed by leukocyte cell numbers and cellular phenotypes in cerebrospinal fluid (CSF) and peripheral blood. METHODS: Cell numbers and cellular phenotypes in CSF and peripheral blood were analyzed in multiple sclerosis (MS) patients treated with natalizumab, untreated MS patients, and patients with other neurological disease (OND). JC virus DNA in the CSF and peripheral blood was quantified by kinetic polymerase chain reaction. RESULTS: CSF leukocyte counts, CD4(+) and CD8(+) T cells, CD19(+) B cells, and CD138(+) plasma cells were significantly lower in natalizumab-treated MS patients compared with OND patients and untreated MS patients. JC virus DNA was not detected in CSF or peripheral blood from natalizumab-treated patients. Six months after cessation of natalizumab therapy, low lymphocyte counts in the CSF persisted. The patient with the highest total leukocyte and CD4(+) and CD8(+)T-cell counts in the CSF experienced a clinical relapse. INTERPRETATION: These data suggest that natalizumab treatment results in a prolonged decrease of lymphocytes in the CSF and are consistent with the hypothesis that natalizumab impairs immune surveillance of the central nervous system.

Adult↗
PubMed2006

Nuclear receptors and autoimmune disease: the potential of PPAR agonists to treat multiple sclerosis.

Experimental autoimmune encephalomyelitis (EAE) is a T-cell-mediated, autoimmune disorder characterized by central nervous system inflammation and demyelination, features reminiscent of the human disease, multiple sclerosis (MS). Prior work in the EAE model has suggested that encephalitogenic T cells are of the T helper (Th)-1 phenotype. Our group has performed several studies in the EAE model that suggest that a strategy for treating autoimmune disorders is to convert the pathogenic cells from the Th1 to Th2 phenotype. Peroxisome proliferator-activated receptors (PPARs) are members of a nuclear hormone receptor superfamily that include receptors for steroids, retinoids, and thyroid hormone, all of which are known to affect the immune response. Recently, we examined the role of PPARgamma in EAE and observed that administration of the PPARgamma agonist 15-deoxy-Delta(12,14) prostaglandin J2 exerted a significant therapeutic effect predominantly by inhibiting the activation and expansion of encephalitogenic T cells. One potential advantage in studying PPARalpha agonists is that they have been very well tolerated when used in humans to treat conditions such as elevated triglycerides. Building on prior work in immune deviation and with PPAR agonists, we have demonstrated that PPARalpha agonists can alter the cytokine phenotype of myelin-reactive T cells, alter their encephalitogenicity, and be useful in the treatment of EAE. The fact that PPARalpha agonists have been used as therapeutic agents in humans to treat metabolic conditions for over 25 years with little toxicity makes them attractive candidates for use as adjunctive therapies in MS.

Autoimmune Diseases↗
PubMed2005

Multiple toll-like receptor agonists act as potent adjuvants in the induction of autoimmunity.

Infections can trigger or exacerbate the course of Multiple Sclerosis, and both bacterial and viral agents have been implicated. These agents are recognized by host cells via pathogen-associated molecular patterns activating TLRs. We investigated the role that PAMPs play in the animal model Experimental Autoimmune Encephalomyelitis, and found various MyD88-dependent PAMPs can participate as the adjuvant to induce EAE. Studies with IRAK1-deficient mice suggest that signaling through TLRs is not required in the target organ to develop disease. This suggests that PAMPs play an important role in priming of autoreactive T cells in EAE and potentially MS.

Adaptor Proteins, Signal Transducing↗
PubMed2005

Agonists for the peroxisome proliferator-activated receptor-alpha and the retinoid X receptor inhibit inflammatory responses of microglia.

The peroxisome proliferator-activated receptor-alpha (PPAR-alpha) plays a key role in lipid metabolism and inflammation. Recently, we demonstrated that administration of the PPAR-alpha agonists gemfibrozil and fenofibrate, inhibit the clinical signs of experimental autoimmune encephalomyelitis (EAE), the animal model of multiple sclerosis (MS). In the present study we investigated the effects of PPAR-alpha agonists on primary mouse microglia, a cell type implicated in the pathology of MS and EAE. Our studies demonstrated that the PPAR-alpha agonists ciprofibrate, fenofibrate, gemfibrozil, and WY 14,643 each inhibited NO production by cytokine-stimulated microglia in a dose-dependent manner. However, fenofibrate and WY 14,643 were more potent inhibitors than gemfibrozil and ciprofibrate. In LPS-stimulated microglia, only fenofibrate and WY 14,643 significantly suppressed NO production. Additionally, PPAR-alpha agonists inhibited the secretion of the proinflammatory cytokines IL-1beta, TNF-alpha, IL-6, and IL-12 p40 and the chemokine MCP-1 by LPS-stimulated microglia. Retinoid X receptors (RXRs) physically interact with PPAR-alpha receptors, and the resulting heterodimers regulate the expression of PPAR-responsive genes. Interestingly, the RXR agonist 9-cis retinoic acid (9-cis RA) inhibited NO production by LPS-stimulated microglia. Furthermore, a combination of 9-cis RA and the PPAR-alpha agonist fenofibrate cooperatively inhibited NO production by these cells. A combination of these agonists also selectively inhibited the expression of proinflammatory cytokines including IL-1beta, TNF-alpha, and IL-6 by LPS-stimulated microglia. Collectively, these results raise the possibility that PPAR-alpha and RXR agonists might have benefit as a therapy in MS, where activated microglia are believed to contribute to disease pathology.

Alitretinoin↗
PubMed2005

Therapeutic considerations for disease progression in multiple sclerosis: evidence, experience, and future expectations.

In the management of patients with multiple sclerosis (MS), providers are all faced with the highly formidable challenge of ascertaining whether, and to what degree, disease-modifying therapy is effective in the individual patient. While much has been learned in randomized, controlled clinical trials, we cannot simply extrapolate the outcomes of these initiatives and apply them to the care of a single patient. In the future, the application of pharmacogenetic techniques, proteomics, and microarray analysis will yield novel profiling information on individual patients that will substantially refine the specific therapeutic questions of relevance: (1) What is the best treatment for an individual patient? (2) Which patients require intensive therapeutic combination regimens to optimize control of the disease process? (3) What are the appropriate drug dosing targets for an individual patient? and (4) Which patients will be predisposed to the development of drug-related adverse events? Such data may provide a novel variable of drug responsiveness that will mandate its inclusion into the process of covariate analyses for clinical trials.

Disease Progression↗
PubMed2005

Effect of rituximab on the peripheral blood and cerebrospinal fluid B cells in patients with primary progressive multiple sclerosis.

BACKGROUND: Rituximab, an anti-CD20 monoclonal antibody that depletes CD20(+) B cells, has demonstrated efficacy in peripheral neurological diseases. Whether this efficacy can be translated to neurological diseases of the central nervous system with possible autoimmune B-cell involvement remains unknown. OBJECTIVE: To determine the effect of rituximab on cerebrospinal fluid B cells in patients with multiple sclerosis. DESIGN: Four patients with primary progressive multiple sclerosis were treated with rituximab. Cerebrospinal fluid and peripheral blood B-cell subsets were identified by flow cytometry from each patient before and after rituximab treatment. RESULTS: The B cells in cerebrospinal fluid were not as effectively depleted as their peripheral blood counterparts. Rituximab treatment temporarily suppressed the activation state of B cells in cerebrospinal fluid. The residual B cells underwent expansion after rituximab treatment. CONCLUSION: The effect(s) of rituximab on the cerebrospinal fluid B-cell compartment is limited in comparison with the effect(s) on the B cells in the periphery, but this finding will need to be confirmed in a larger group of MS patients.

Adult↗
PubMed2005

Recommended standard of cerebrospinal fluid analysis in the diagnosis of multiple sclerosis: a consensus statement.

New criteria for the diagnosis of multiple sclerosis (MS) were published as the result of an internationally formed committee. To increase the specificity of diagnosis and to minimize the number of false diagnoses, the committee recommended the use of both clinical and paraclinical criteria, the latter involving information obtained from magnetic resonance imaging, evoked potentials, and cerebrospinal fluid (CSF) analysis. Although rigorous magnetic resonance imaging requirements were provided, the "new criteria paper" fell short in terms of guidelines as to how the CSF analysis should be performed and simply equated the IgG index with isoelectric focusing, without any justification. The spectrum of parameters analyzed and methods for CSF analysis differ worldwide and often yield variable results in terms of sensitivity, specificity, accuracy, and reliability, with no decided "optimal" CSF test for the diagnosis of MS. To address this question specifically, an international panel of experts in MS and CSF diagnostic techniques was convened and the result was this article, representing a consensus of all the participants. These recommendations for establishing a standard for the evaluation of CSF in patients suspected of having MS should greatly complement the new criteria in ensuring that a correct diagnosis of MS is being made.

Consensus Statements as Topic↗