Natalizumab treatment is associated with peripheral sequestration of proinflammatory T cells.

BACKGROUND: Natalizumab is an antibody directed against integrin alpha4 that reduces disease activity in patients with multiple sclerosis (MS) by blocking migration of T and B cells into the CNS. The goal of this study was to characterize the effects of natalizumab treatment on cytokine production and expression of activation markers, costimulatory molecules, and trafficking determinants on CD4+ and CD8+ T cells. METHODS: In a longitudinal study, we investigated the expression of surface makers and cytokine expression on peripheral blood lymphocytes from 28 patients with MS who started natalizumab treatment and were followed for 1 year. A mixed effects model was used to compare pretreatment to on-treatment measurements. RESULTS: The frequency of CD4+ T cells producing interferon-gamma, tumor necrosis factor, and interleukin (IL)-17 upon anti-CD3 stimulation increased 6 months after initiation of natalizumab treatment and remained elevated throughout the follow-up. The frequency of CD4+ T cells expressing CD25, HLA-DR, and CCR6 ex vivo was increased at one or more time points during treatment. Among CD8+ T cells, the frequency of cells producing IL-2 and IL-17 after stimulation was increased during natalizumab treatment, as was the frequency of CD8+ T cells expressing CD58 and CCR5 ex vivo. The increase in the frequency of activated cells could not be replicated by in vitro exposure to natalizumab. CONCLUSION: Natalizumab treatment increases the percentage of activated leukocytes producing proinflammatory cytokines in blood, presumably due to sequestration of activated cells in the peripheral circulation.

Multiple sclerosis: chemokine receptor expression on circulating lymphocytes in correlation with radiographic measures of tissue injury.

BACKGROUND: Leukocytes expressing inflammatory chemokine receptors (CKRs), most consistently CCR2, CCR5, and CXCR3, have been identified in multiple sclerosis (MS) tissue lesions and provide attractive therapeutic targets. Our previous studies found large inter-individual differences in expression of these CKRs but stable levels over time within subjects. This observation suggests a CKR "set-point" within individuals, which might relate to inflammatory injury in MS. We evaluated the correlation between CKR levels and magnetic resonance imaging (MRI) measures of disease activity. METHODS: Fifty-five relapsing remitting MS (RRMS) and secondary progressive MS (SPMS) patients were prospectively followed with annual CKR and MRI studies. Multiparameter flow cytometry was used to determine CCR2, CCR5, and CXCR3 expression on CD4 and CD8 cells. Simultaneous cranial MRIs were performed, and quantitative measures of T2, T1, and gadolinium lesions, brain parenchymal fraction (BPF), and whole brain and fractionated magnetization transfer ratio (MTR) were performed using automated software. Spearman's rank correlations evaluated the relationship between CKR levels and MRI measures. RESULTS: Significant correlations were observed between CXCR3 expression on CD8 cells and measures of new (T1) and total (T1, T2) lesion volumes, lesion MTR, and BPF; higher levels of CXCR3 expression were correlated with greater injury on MRI (|r| = 0.27-0.42). In contrast, CD4 cell CKR expression was only minimally correlated with MRI measures. CONCLUSIONS: Over 2 years, we observed significant correlations between the percent of CD8 cells expressing CXCR3 and MRI measures of MS inflammatory activity and tissue destruction. These observations are consistent with a pathogenic role for cytotoxic T cells in MS brain and have significant implications regarding T-cell targeted therapeutic strategies.

Multiple sclerosis: a study of chemokine receptors and regulatory T cells in relation to MRI variables.

Magnetic resonance imaging (MRI) remains the most valuable tool for monitoring disease activity and progression in patients with multiple sclerosis (MS), a chronic demyelinating disease of the central nervous system (CNS) with presumably autoimmune etiology. Chemokine receptors have been implicated in MS as key molecules directing inflammatory cells into the CNS. Regulatory (CD4+CD25+) T cells (Tr cells) are important in suppressing autoimmunity, and their absolute or functional deficit could be expected in MS. In the present study, venous blood was obtained from MS patients concurrent with MRI examination of the brain, and expression of chemokine receptors CCR1, CCR2, CCR5, CXCR3 and CXCR4 by CD4 T cells and monocytes, proportions of Tr cells, as well as expression of CD45RO, CD95, CTLA-4, HLA-DR and interleukin (IL)-10 by Tr cells and non-Tr (CD25-) CD4 T cells was analyzed by flow cytometry. Surface expression of CXCR3 by CD4 T cells was downregulated in the group of patients with high lesion load (LL) on T2-weighted images and gadolinium (Gd)-enhancing lesions on T1-weighted images, compared to the group with high LL and no Gd-enhancing lesions, and to the group with low LL, suggesting internalization of CXCR3 due to the release of its chemokine ligand (IP-10/CXCL10) from active MS lesions. Proportions of Tr cells amongst all CD4 T cells, and expression of IL-10 by Tr cells were increased in the patients with high LL and Gd-enhancing lesions. These results suggest that there is correlation between MRI parameters, chemokine receptor expression and the status of circulating Tr cells in MS, but further studies need to discriminate between pathogenetically relevant and bystander phenomena.

T-cells in the cerebrospinal fluid express a similar repertoire of inflammatory chemokine receptors in the absence or presence of CNS inflammation: implications for CNS trafficking.

It is believed that chemokines and their receptors are involved in trafficking of T-cells to the central nervous system (CNS). The aim of the current study was to define the expression on cerebrospinal fluid (CSF) T-cells of six chemokine receptors associated with trafficking to sites of inflammation. Flow cytometry was used to detect chemokine receptor expression. We observed that CD3+T-cells in the CSF express a restricted array of inflammatory chemokine receptors, specifically CXCR3, CCR5 and CCR6, but little CCR1-3. This repertoire was independent of the presence of CNS inflammation, since comparable findings were obtained in patients with multiple sclerosis (MS) and individuals with non-inflammatory neurological diseases. The enrichment of CCR5+T-cells in the CSF could largely be explained by higher frequency of CD4+/CD45RO+T-cells in this compartment. In contrast, CD4+/CD45RO+T-cells expressing CXCR3 were significantly enriched in CSF as compared with blood. Similar levels of CCR6+/CD3+T-cells were observed in blood and CSF, while levels of CCR2+/CD3+T-cells were lower in CSF than in blood. The CSF was virtually devoid of CCR5+/CXCR3- T-cells, suggesting that the expression of CCR5 alone is not sufficient for the trafficking of CD3+T-cells to the CSF. We hypothesize that CXCR3 is the principal inflammatory chemokine receptor involved in intrathecal accumulation of T-cells in MS. Through interactions with its ligands, CXCR3 is proposed to mediate retention of T-cells in the inflamed CNS.

CCR1+/CCR5+ mononuclear phagocytes accumulate in the central nervous system of patients with multiple sclerosis.

Mononuclear phagocytes (monocytes, macrophages, and microglia) are considered central to multiple sclerosis (MS) pathogenesis. Molecular cues that mediate mononuclear phagocyte accumulation and activation in the central nervous system (CNS) of MS patients may include chemokines RANTES/CCL5 and macrophage inflammatory protein-1alpha/CCL3. We analyzed expression of CCR1 and CCR5, the monocyte receptors for these chemokines, on circulating and cerebrospinal fluid CD14+ cells, and in MS brain lesions. Approximately 70% of cerebrospinal fluid monocytes were CCR1+/CCR5+, regardless of the presence of CNS pathology, compared to less than 20% of circulating monocytes. In active MS lesions CCR1+/CCR5+ monocytes were found in perivascular cell cuffs and at the demyelinating edges of evolving lesions. Mononuclear phagocytes in early demyelinating stages comprised CCR1+/CCR5+ hematogenous monocytes and CCR1-/CCR5- resident microglial cells. In later stages, phagocytic macrophages were uniformly CCR1-/CCR5+. Cultured in vitro, adherent monocytes/macrophages up-regulated CCR5 and down-regulated CCR1 expression, compared to freshly-isolated monocytes. Taken together, these findings suggest that monocytes competent to enter the CNS compartment derive from a minority CCR1+/CCR5+ population in the circulating pool. In the presence of ligand, these cells will be retained in the CNS. During further activation in lesions, infiltrating monocytes down-regulate CCR1 but not CCR5, whereas microglia up-regulate CCR5.

Chemokine-based therapies for MS: how do we get there from here?

The workshop on Multiple Sclerosis and Chemokines: Prospects for Therapeutic and Prophylactic Intervention was held in Chevy Chase, MD, USA, from 9-10 July 2001.

Absence of monocyte chemoattractant protein 1 in mice leads to decreased local macrophage recruitment and antigen-specific T helper cell type 1 immune response in experimental autoimmune encephalomyelitis.

Monocyte chemoattractant protein (MCP)-1 plays a critical role in innate immunity by directing the migration of monocytes into inflammatory sites. Recent data indicated a function for this chemokine in adaptive immunity as a regulator of T cell commitment to T helper cell type 2 (Th2) effector function. Studies in a Th1-dependent animal model, experimental autoimmune encephalomyelitis (EAE), showed that MCP-1 was highly expressed in the central nervous system (CNS) of affected rodents, and MCP-1 antibodies could block relapses of the disease. Mice deficient for the major MCP-1 receptor, CC chemokine receptor (CCR)2, did not develop EAE after active immunization but generated effector cells that could transfer the disease to naive wild-type recipients. We analyzed EAE in mice deficient for MCP-1 to define the relevant ligand for CCR2, which responds to murine MCP-1, MCP-2, MCP-3, and MCP-5. We found that C57BL/6 MCP-1-null mice were markedly resistant to EAE after active immunization, with drastically impaired recruitment of macrophages to the CNS, yet able to generate effector T cells that transferred severe disease to naive wild-type recipients. By contrast, adoptive transfer of primed T cells from wild-type mice into naive MCP-1-null recipients did not mediate clinical EAE. On the SJL background, disruption of the MCP-1 gene produced a milder EAE phenotype with diminished relapses that mimicked previous findings using anti-MCP-1 antibodies. There was no compensatory upregulation of MCP-2, MCP-3, or MCP-5 in MCP-1-null mice with EAE. These results indicated that MCP-1 is the major CCR2 ligand in mice with EAE, and provided an opportunity to define the role of MCP-1 in EAE. Compared with wild-type littermates, MCP-1-/- mice exhibited reduced expression of interferon gamma in draining lymph node and CNS and increased antigen-specific immunoglobulin G1 antibody production. Taken together, these data demonstrate that MCP-1 is crucial for Th1 immune responses in EAE induction and that macrophage recruitment to the inflamed CNS target organ is required for primed T cells to execute a Th1 effector program in EAE.

Altered expression of costimulatory molecules in myasthenia gravis.

To characterize the involvement of costimulatory pathways in the pathogenesis of myasthenia gravis (MG), a multiparameter flow cytometry assay was adopted to enumerate blood mononuclear cells (MNC) expressing CD28, CD80, CD86, CD40, and CD40L molecules in patients with MG and healthy subjects. Patients with MG had lower percentages of CD8(+)CD28(+) cells, augmented percentages of CD4(+)CD80(+), CD4(+)CD86(+), CD8(+)CD80(+), CD8(+)CD86(+), CD14(+)CD80(+), and CD14(+)CD86(+) cells, and similar levels of cells expressing CD40 and CD40L and of B cells expressing CD80 and CD86 compared to the controls. Patients with early onset of MG (<40 years) had lower percentages of CD3(+)CD86(+), CD4(+)CD86(+), CD8(+)CD86(+) T cells and CD20(+)CD86(+) B cells compared to those with late onset (>40 years). There was a positive correlation between the patients' age and percentages of CD86(+) cells. The data indicate that the CD28/CD80-CD86 costimulatory pathway is involved in MG. The high percentages of CD80 and CD86 positive T cells and monocytes may reflect persistent activation of T and B cells, whereas the low CD28 expression may be the result of chronic exposure to CD80 and CD86. These molecules could be the focus for new and improved immunomodulating therapies of MG.

Neutralizing and binding anti-interferon-beta (IFN-beta) antibodies. A comparison between IFN-beta-1a and IFN-beta-1b treatment in multiple sclerosis.

Interferon-beta (IFN-beta) is currently the most commonly used treatment of relapsing-remitting multiple sclerosis (MS). At the time of this study, two preparations of IFN-beta were available, IFN-beta-1a (Avonextrade mark) and IFN-beta-1b (Betaferon(R)), which both can elicit an immune response with the development of anti-IFN-beta antibodies. Direct comparisons between these two preparations regarding antibody frequencies have, however, been difficult to perform, because two different analysis methods measuring partly different biological effects of IFN-beta have been employed. In the present study, binding and neutralizing anti-IFN-beta-1a and -1b antibodies were detected in parallel by an independent, well-acknowledged, interferon research laboratory using an immunoassay and a cytopathic virus inhibition assay. Five per cent of patients treated with IFN-beta-1a intramuscularly (n = 20) had neutralizing antibodies (NABs) compared with 44% of patients treated with IFN-beta-1b subcutaneously (n = 48). A high degree of cross-reactivity between neutralizing anti-IFN-beta-1a and -1b antibodies was observed. No effect of NABs on clinical outcome could be detected in this limited material. Binding anti-IFN-beta antibodies were observed in 20% of IFN-beta-1a treated patients compared with 81% of patients treated with IFN-beta-1b. Only one of 17 patients examined (6%) had detectable titres of binding anti-IFN-beta-1b antibodies in the cerebrospinal fluid (CSF). These data are the first using identical methodology to show that IFN-beta-1a gives rise to fewer NABs than IFN-beta-1b at recommended treatment schedules.

Multiple sclerosis is associated with an imbalance between tumour necrosis factor-alpha (TNF-alpha)- and IL-10-secreting blood cells that is corrected by interferon-beta (IFN-beta) treatment.

The up-regulated B cell responses detectable in cerebrospinal fluid (CSF) and the augmented myelin antigen-specific T cell responses observed in the CSF as well as systematically in patients with multiple sclerosis (MS) suggest the involvement of cytokines in disease development and perpetuation. Here we report on the parallel involvement of TNF-alpha, IL-6, IFN-gamma and IL-10 in MS and controls, using enzyme-linked immunospot (ELISPOT) assays to detect and enumerate cytokine-secreting mononuclear cells (MNC) prepared from blood and, for IL-6 and IL-10, from CSF without in vitro stimulation. MS is associated with elevated levels of TNF-alpha-secreting blood MNC when compared with levels in groups of control patients with myasthenia gravis (MG) and other neurological diseases (OND) or healthy subjects. This elevation was confined to patients with untreated MS and not present in those examined during ongoing treatment with IFN-beta. Untreated patients with MS had lower numbers of IL-10-secreting blood MNC compared with the three control groups. In patients undergoing treatment with IFN-beta, numbers of IL-10-secreting cells were in the same range as in controls. Normalization of TNF-alpha from elevated, and of IL-10 from decreased levels could be one reason for the beneficial effects of IFN-beta in MS, although it remains to be shown whether these changes reflect phenomena primarily involved in MS pathogenesis or secondary changes. In CSF, levels of IL-10-secreting cells were higher than in blood in both MS and OND, with no difference between these groups. Systemic aberrations of IL-6 and IFN-gamma and of IL-6 in CSF in MS versus controls were only minor, irrespective of treatment with IFN-beta.

Elevated CD40 ligand expressing blood T-cell levels in multiple sclerosis are reversed by interferon-beta treatment.

Myelin protein reactive CD4+ T cells are considered to be involved in the proposed immunopathogenesis of multiple sclerosis (MS). One particularly important molecule for T-cell activation is the CD40L (gp39) that is expressed on the surface of T cells. This study focuses on the CD40 and the CD40L expression on mononuclear cells prepared from blood from patients with MS, other neurological diseases (OND) and healthy subjects. Immunostaining followed by a three channel flow cytometry was adopted. Patients with MS had higher levels of CD3+CD40L+, CD4+CD40L+ and CD8+CD40L+ T cells compared to patients with OND and healthy subjects. Cross-sectional comparisons revealed that the elevation of CD40L+ T cell subtypes was confined to the patients with untreated MS and not observed in the patients with MS treated with interferon-beta (IFN-beta). Follow up studies showed that levels of CD3+CD40L+ and CD4+CD40L+ T cells decreased in individual patients after the initiation of the IFN-beta treatment. The enhanced expression of CD40L on CD3+, CD4+ and CD8+ T cells in patients with MS may implicate a role for this molecule in disease immunopathogenesis.

Regression analysis of metabolite concentrations estimated from localized proton MR spectra of active and chronic multiple sclerosis lesions.

Localized short echo time magnetic resonance (MR) spectra were obtained from patients with multiple sclerosis of relapsing-remitting or secondary chronic-progressive course and from healthy controls. Automated analysis using model spectra, sensitivity correction, and subtraction of partial ventricular volume yielded tissue concentrations of metabolites that were in line with findings of previous studies. Additional findings were increased creatine in chronic lesions and increased myo-inositol in normal-appearing white matter. Regression analysis was performed to reveal concomitant changes of metabolite concentrations. Differences in the correlations between cholines and myo-inositol suggest increased expression of myo-inositol in chronic lesions or of cholines in active, contrast-enhanced lesions. A correlation between N-acetyl-aspartate and creatine, which is probably due to extracellular edema, was observed in active but not in chronic lesions. Creatine and cholines correlated in chronic lesions, which may be the result of gliosis. The consequences of these findings for the interpretation of absolute concentrations and creatine ratios are discussed.

Increased levels of circulating acetylcholine receptor (AChR)-reactive IL-10-secreting cells are characteristic for myasthenia gravis (MG).

Antibodies to the nicotinic AChR are pivotal in the immunopathogenesis of MG. Cytokines produced by T-helper cells are important regulators of humoral immune responses. IL-10 is considered an anti-inflammatory cytokine, but it promotes B cell activation and worsens experimental autoimmune MG in Lewis rats, an experimental model of MG. To study IL-10 and, as a control, interferon-gamma (IFN-gamma) in MG, we used an enzyme-linked immunospot (ELISPOT) assay, thereby assessing numbers of blood mononuclear cells (MNC) secreting IL-10 and IFN-gamma spontaneously and after stimulation with AChR. Low numbers of IL-10-secreting cells were regularly found in peripheral blood from patients with MG as well as in controls with other neurological diseases and healthy subjects. However, only MG patients had elevated blood levels of AChR-reactive IL-10- and IFN-gamma-secreting cells. The MG patients showed no responses to the control autoantigen myelin basic protein, underlining the specificity of the IL-10 and IFN-gamma responses. Immunosuppressive treatment reduced numbers of AChR-reactive IFN-gamma-secreting cells but increased the numbers of IL-10-secreting cells. The numbers of IL-10-secreting cells tended to be higher in patients with generalized versus ocular MG, further suggesting that the augmented IL-10 responses may be important in the pathogenesis and perpetuation of MG.

Increased IL-1beta, IL-8, and IL-17 mRNA expression in blood mononuclear cells observed in a prospective ischemic stroke study.

BACKGROUND AND PURPOSE: Ischemic brain injury secondary to arterial occlusion is characterized by acute local inflammation, which involves accumulation of polymorphonuclear neutrophils (PMN). Factors that influence the recruitment of PMN could represent new therapeutic targets in acute stroke. In this prospective study we evaluated numbers of peripheral blood mononuclear cells (PBMC) expressing mRNA for interleukin (IL)-1beta, IL-8, and IL-17 and macrophage inflammatory protein-1alpha (MIP-1alpha) after ischemic stroke. METHODS: Peripheral blood was obtained on days 1 to 3, 4 to 10, and 20 to 31 after onset of symptoms. In situ hybridization with radiolabeled synthetic oligonucleotide probes was adopted to measure cytokine mRNA expression in PBMC. Plasma and cerebrospinal fluid levels of IL-8 were measured by an enzyme-linked immunosorbent assay. RESULTS: Most patients with ischemic stroke had clearly elevated numbers of IL-1beta, IL-8, and IL-17 mRNA expressing PBMC 1 to 3 days after onset of symptoms compared with healthy individuals (P<0. 0001 for all comparisons). At follow-up after 20 to 31 days, numbers of IL-8 mRNA expressing PBMC were lower than during the acute stage (P<0.001), but only IL-1beta and IL-17 mRNA expression had returned to the level of the healthy individuals. Numbers of MIP-1alpha mRNA expressing PBMC did not differ between patients with ischemic stroke and healthy individuals at any time point. A correlation was observed between numbers of IL-1beta, IL-8, and IL-17 mRNA expressing PBMC and the degree of neurological impairment as measured by the Scandinavian Stroke Scale 1 to 3 days after onset of symptoms (r=0.5; P<0.01 for all correlations). CONCLUSIONS: A longitudinal study of patients with ischemic stroke revealed systemic increases of levels of IL-1beta, IL-8, and IL-17 that correlated with Scandinavian Stroke Scale scores. IL-8 levels were further increased in cerebrospinal fluid.

Levels of interleukin-15-expressing blood mononuclear cells are elevated in multiple sclerosis.

Interleukin-15 (IL-15) is a novel IL-2-like cytokine expressed by cells of the monocyte/macrophage and epithelial lineages. Cytokines might be involved in the pathogenesis of multiple sclerosis (MS). Using immunocytochemistry, we analysed spontaneous expression of IL-15 by peripheral blood (PB) and cerebrospinal fluid (CSF) mononuclear cells (MNC) from patients with MS, other neurological diseases (OND) and healthy controls. IL-15- positive peripheral blood mononuclear cells (PBMNC) were elevated in patients with MS compared to healthy controls (P < 0.05). The elevation of IL-15- positive PBMNC was restricted to patients with chronic progressive MS and not observed in patients studied during the relapsing-remitting phase of MS. The numbers of IL-15- expressing PBMNC correlated with the duration and disability of MS (r = 0.45, P < 0.001, and r = 0.39, P < 0.01, respectively). IL-15 was undetectable in CSF MNC, and ELISA showed low CSF levels of IL-15 in occasional patients with MS and OND. IL-15 is a potent growth factor for gammadelta T cells, but there was no correlation between IL-15 expression by PBMNC and percentage of gammadelta T cells in blood from the MS patients. Together, these data demonstrate that IL-15 expression by PBMNC is upregulated in the chronic stage of MS.

High numbers of perforin mRNA expressing CSF cells in multiple sclerosis patients with gadolinium-enhancing brain MRI lesions.

Enhanced expression of pro- and anti-inflammatory cytokines is a common finding in MS, but attempts to correlate cytokine expression with disease activity have produced conflicting results. In this paper, gadolinium-(Gd-)enhancing lesions on brain MRI were used as markers for active inflammation in patients with MS not treated with any immunomodulatory drugs. In parallel, in situ hybridization was used to detect blood and cerebrospinal fluid (CSF) mononuclear cells (MNC) expressing cytokine mRNA. An association was observed between numbers of perforin mRNA expressing CSF MNC and numbers of Gd-enhancing brain MRI lesions. Perforin mRNA expressing CSF MNC were not detected in any of the patients lacking active lesions on brain MRI. The expression of tumor necrosis factor-alpha, interleukin-10 (IL-10) and IL-12 mRNA in CSF MNC did not differ between MS patients with and without active MRI lesions. Based on the present finding, a role for perforin in the disruption of the blood-brain barrier in MS can be hypothesized.

High levels of IL-10 secreting cells are present in blood in cerebrovascular diseases.

Ischemic stroke is associated with altered systemic immune responses both early after the onset and in the recovery phase. Interleukin (IL)-10, a Th2 related cytokine, has multiple effects on different cell types, including T and B lymphocytes, monocytes, neutrophils and mast cells. IL-4 is another Th2 cytokine that inhibits the synthesis of pro-inflammatory cytokines by Th1 clones. We used enzyme-linked immunospot assays to detect and enumerate blood mononuclear cells (MNC) secreting IL-10 and IL-4 spontaneously as well as after stimulation with myelin basic protein (MBP), considered to be an autoantigen of possible pathogenic importance in, for example, multiple sclerosis, to evaluate the involvement of anti-inflammatory cytokines in ischemic stroke. All patients with ischemic stroke and cerebral hemorrhage had strongly elevated numbers of IL-10 secreting blood MNC compared with healthy individuals. Numbers of MBP-reactive IL-10 secreting blood MNC were also elevated in a proportion of the patients with stroke and hemorrhage. Levels of IL-4 secreting blood MNC did not differ in ischemic stroke versus healthy individuals. The anti-inflammatory IL-10 could play a pivotal role in ischemic stroke as well as cerebral hemorrhage.

Interleukin-17 mRNA expression in blood and CSF mononuclear cells is augmented in multiple sclerosis.

Myelin-directed autoimmunity is considered to play a key role in the pathogenesis of multiple sclerosis (MS). Increased production of both pro- and anti-inflammatory cytokines is a common finding in MS. Interleukin-17 (IL-17) is a recently described cytokine produced in humans almost exclusively by activated memory T cells, which can induce the production of proinflammatory cytokines and chemokines from parenchymal cells and macrophages. In situ hybridisation with synthetic oligonucleotide probes was adopted to detect and enumerate IL-17 mRNA expressing mononuclear cells (MNC) in blood and cerebrospinal fluid (CSF) from patients with MS and control individuals. Numbers of IL-17 mRNA expressing blood MNC were higher in patients with MS and acute aseptic meningoencephalitis (AM) compared to healthy individuals. Higher numbers of IL-17 mRNA expressing blood MNC were detected in MS patients examined during clinical exacerbation compared to remission. Patients with MS had higher numbers of IL-17 mRNA expressing MNC in CSF compared to blood. This increase in numbers of IL-17 mRNA expressing MNC in CSF was not observed in patients with AM. Our results thus demonstrate increased numbers of IL-17 mRNA expressing MNC in MS with higher numbers in CSF than blood, and with the highest numbers in blood during clinical exacerbations.