Anne Lise Karlsgot Hestvik

Multiple sclerosis: immunopathogenesis and controversies in defining the cause.

Purpose of review Multiple sclerosis is a major cause of neurological disability in Western societies. The most important reason for the limited success obtained in the treatment and prevention so far is most likely related to the limited knowledge about its cause and pathogenesis. This paper discusses recent progress and controversies in the understanding of the pathogenesis and cause of multiple sclerosis. Recent findings Both T helper cells type 1 (Th1 cells), Th17 cells, cytotoxic T cells, B cells and regulatory T cells are involved in the inflammatory process. Axonal loss seems to be driven by inflammation during the early stages of disease but may become independent of inflammation at later stages. The target antigen of the immune response has not been identified. Weak genetic association has been established in two cytokine receptors, whereas increasing female: male ratio support the importance of environmental risk factors. A substantial proportion of intrathecal B cells are infected with Epstein–Barr virus. Summary Multiple sclerosis is a complex disease and calls for integrated efforts from immunology, epidemiology, neuroscience and genetics. In particular, the immunological implications of environmental risk factors such as vitamin D desufficiency, smoking and Epstein–Barr virus infection need to be explored.

Cerebrospinal fluid T cell responses against glutamic acid decarboxylase 65 in patients with stiff person syndrome

Most patients with stiff person syndrome (SPS) display intrathecal synthesis of oligoclonal and high-avidity IgG against the 65 kDa isoform of glutamic acid decarboxylase (GAD65 IgG), but little is known about the mechanisms driving this immune response. We hypothesized that GAD65-specific T cells accumulating in the central nervous system drive the intrathecal GAD65 IgG production. Accordingly, we were able to clone HLA-DR or DP restricted GAD65-specific T cells from the cerebrospinal fluid (CSF) of all three patients with, but not in one patient without substantial intrathecal production of GAD65 IgG. The CSF T cells recognized four GAD65 epitopes, which were unique to each patient. In two patients, identical or closely related GAD65-specific CSF T cell clones were expanded in vivo. In contrast to the findings in CSF, only one GAD65-specific T cell clone could be raised from the blood of one single patient. Cysteine in amino acid position 474, which is important for enzymatic function of GAD65, was critical for recognition of GAD65(474-484) by HLA-DP restricted CSF T cells. We conclude that GAD65-specific T cells and clonally expanded GAD65-specific B cells coexist intrathecally, where they may collaborate in the synthesis of GAD65 IgG.

GAD65 IgG autoantibodies in stiff person syndrome: clonality, avidity and persistence

Background and purpose:  Persistent intrathecal production of IgG autoantibodies against glutamic acid decarboxylase 65 (GAD65 IgG) and oligoclonal IgG of undetermined specificity has been reported in stiff person syndrome (SPS).

Cerebrospinal fluid T cell clones from patients with multiple sclerosis : recognition of idiotopes on monoclonal IgG secreted by autologous cerebrospinal fluid B cells

Due to somatic recombination and hypermutation, Ig variable heavy (VH) and light (VL) regions contain unique immunogenic determinants, idiotopes (Id), which can stimulate T cells. To address the relevance of this in a human disease, monoclonal IgG (mAb)‐secreting B cell clones were established from the cerebrospinal fluid (CSF) of two patients with multiple sclerosis (MS). HLA‐DR‐restricted CD4+ T cell lines and clones from CSF of both patients specifically recognized autologous CSF mAb. The CSF T cell clones produced IFN‐γ; some also produced TNF‐α, IL‐10 and IL‐5. VH and VL on the monoclonal IgG derived from CSF B cells expressed amino acid replacements due to somatic mutations. A T cell epitope was mapped to a VH framework region, where an amino acid replacement was critical for the T cell recognition. The finding of Id‐specific T cells and Id‐bearing B cells in the CSF indicates that they coexist within the diseased organ, and provide a basis for the study of Id‐driven T–B cell collaboration in a human autoimmune disease.

T cells from multiple sclerosis patients recognize multiple epitopes on Self-IgG.

Abstract The highly diversified variable regions of immunoglobulin (Ig) molecules contain immunogenic determinants denoted idiotopes. We have previously reported that T cells from multiple sclerosis (MS) patients recognize IgG from autologous cerebrospinal fluid (CSF), and mapped a T‐cell epitope to an IgG idiotope. To test the ability of CSF IgG molecules to elicit a broad polyclonal T‐cell response in MS, we have analysed T‐cell responses in the blood and CSF against idiotope peptides spanning complementarity determining region (CDR) 3 and somatic mutations within the variable regions of monoclonal CSF IgG. Consistent with a diversified idiotope‐specific T‐cell repertoire, CD4+ T cells from both patients recognized several idiotope peptides presented by HLA‐DR molecules. Mutations were critical for T‐cell recognition, as T cells specific for a mutated CDR1 peptide did not recognize corresponding germline‐encoded peptides. One T‐cell clone recognized both an idiotope peptide and the B‐cell clone expressing this idiotope, compatible with endogenous processing and presentation of this idiotope by B cells. These results suggest that mutated CSF IgG from MS patients carry several T‐cell epitopes, which could mediate intrathecal IgG production and inflammation in MS through idiotope‐driven T–B‐cell collaboration.

Expression and functional activity of chemokine receptors in glatiramer acetate-specific T cells isolated from multiple sclerosis patient receiving the drug glatiramer acetate.

The purpose of the current study is to examine the surface expression of chemokine receptors and the chemotaxis toward the respective chemokines of glatiramer acetate (GA)-specific CD4(+) T cells isolated from the blood and the cerebrospinal fluid (CSF) of a multiple sclerosis (MS) patient. Four clones were selected, two isolated from the peripheral blood and two from the CSF. CCR4 and CXCR3 were expressed on all four clones. Both blood-derived clones also expressed CCR5 and, to a lesser extent, CCR6. Similarly, one CSF clone expressed CCR5 and CCR6. In contrast, CCR1, CCR2, CCR3, CCR7, CCR9, CCR10, CXCR1, CXCR4, CXCR5, CXCR6, and CCR6 were either expressed on few cells or were not expressed at all on all four clones examined. The expression of chemokine receptors was corroborated with the ability of the cells to respond chemotactically to the corresponding chemokines, CCL5/RANTES, CCL20/MIP-3α, CCL22/MDC and CXCL10/IP-10. Both the receptor expression and chemotaxis were reduced upon activation with PMA and ionomycin. The shared expression of chemokine receptors and the migration patterns suggest that GA-reactive cells have migrated from the blood into the CSF, and that local reactivation within the inflamed CSF may downregulate the expression of chemokine receptors and hence impede their migration intrathecally. The results may also explain the beneficial synergistic effects of combining immunosuppressive drugs with GA in MS patients.

Idiotope-specific CD4(+) T cells induce apoptosis of human oligodendrocytes.

CD4(+) T cells specific for immunologic non-self determinants on self-IgG, idiotopes (Id), can be raised from cerebrospinal fluid (CSF) and blood of patients with multiple sclerosis (MS). To test if Id-specific CD4(+) T cells have the potential to destroy oligodendrocytes (ODCs), we analyzed their ability to induce apoptosis of human ODC cell lines. Id-specific CD4(+) T cells stimulated with either Id-bearing B cells, Id-peptide presented by other antigen presenting cells, or by anti-CD3/anti-CD28 in the absence of accessory cells induced DNA fragmentation and killed ODCs. Killing required contact between the ODCs and the T cells, it did not depend on the cytokine profile of the T cells, it was independent of other cell types, and was inhibited by a general caspase inhibitor and an anti-Fas antibody. Activated CD4(+) T cells specific for glutamic acid decarboxylase 65 also induced apoptosis, showing that killing does not depend on cognate interaction between T cells and target cells but rather on the activation status of the T cells.

The idiotype connection: linking infection and multiple sclerosis

B cells present idiotopes (Id) from their B cell receptor to Id-specific CD4(+) T cells. Chronic Id-driven T-B cell collaboration can cause autoimmune disease in mice. We propose that Id-driven T-B cell collaboration mediates the development of multiple sclerosis by perpetuating immune responses initiated against infectious agents. During germinal centre reactions, B cells express a multitude of mutated Ids. While most mutations lead to decreased affinity and deletion of the B cell, some B cells could be rescued by Id-specific T cells. Such Id-connected T-B cell pairs might initiate inflammatory foci in the central nervous system. This model may explain the intrathecal synthesis of low-avidity IgG against viruses, and the synthesis of oligoclonal IgG with unknown specificity in multiple sclerosis.

Protective and detrimental immunity: lessons from stiff person syndrome and multiple sclerosis

Background – The immune system may attack the brain and cause inflammatory disorders like multiple sclerosis (MS). On the other hand, the immune system may protect and support neurons. Methods– There are two obstacles to study this paradox in humans. First, the target antigens in many human central nervous system (CNS) disorders are unknown. Second, it is often difficult to separate pathogenic from protective events, as well as primary from secondary phenomena. Idiopathic stiff person syndrome (SPS) circumvents the first obstacle, because most patients secrete antibodies against glutamic acid decarboxylase (GAD) 65. The immune response against glatiramer acetate (GA) may circumvent the second obstacle. Migration of activated T helper cells to the intrathecal compartment could be a common denominator in GA treatment and SPS. Results– We here discuss recent results on T cells in MS and SPS, showing that GAD65‐specific and GA‐reactive lymphocytes in the cerebrospinal fluid are not a simple reflection of those in blood. Conclusion– The rules and mechanisms governing T cell selection and maintenance in the CNS may provide a key to the understanding of protective and detrimental aspects of CNS immunity.

Management of progressive multifocal leukoencephalopathy associated with natalizumab – possibilities and responsibility

Natalizumab is a promising drug for the treatment of multiple sclerosis [1], and could also be useful for other autoimmune diseases. However, the manufacturer has removed the drug from the market as three patients treated with natalizumab were found to have developed progressive multifocal leukoencephalopathy (PML). Two of these patients have died and one has survived with mental sequelae [2,3]. Natalizumab is a monoclonal antibody against the adhesion molecule a4b1 integrin, and its effect on multiple sclerosis has been attributed to the blocking of lymphocyte migration to the central nervous system. However, lymphocytes are needed to keep the JC virus in check, and the development of PML in these patients was probably a consequence of distorted immunosurveillance leading to unbridled JC virus replication [4]. In patients with AIDS who develop PML, survival is associated with immune reconstitution [5]. The logical treatment for PML associated with natalizumab would be to remove or neutralize the drug. Plasma exchange, and perhaps also intravenous immunoglobulin (IVIG), probably enhances the clearance of natalizumab. However, the biological effect of the drug could probably be more rapidly and effectively neutralized by infusion of an anti-idiotypic antibody against natalizumab. Anti-idiotypic antibodies bind specifically to the antigen-binding site on the hypervariable regions of antibodies. An anti-idiotypic antibody could therefore be designed to target natalizumab specifically, which would allow rapid intrathecal immune reconstitution by reducing the blocking of a4 integrin. Interestingly, in a controlled clinical trial, natalizumab was found to have no clinical effect and no serious adverse effects in patients who had developed antibodies against the drug [1]. Although this result could be a long-term effect of the anti-natalizumab antibodies, the neutralizing effect of these antibodies is an indicator of the safety and potential usefulness of treatment with anti-idiotypic antibodies. Several questions needs to be answered before plasma exchange, IVIG or antiidiotypic antibodies can be tried for the treatment of PML associated with natalizumab. First, their efficacy in the clearance of natalizumab must be established. This also applies to their effect on adhesion molecules already blocked by natalizumab and on the expression of new adhesion molecules. The impact on intrathecal immune reconstitution, the timewindow and safety of these treatment modalities must be determined. Thus, developing an anti-idiotypic antibody, pre-clinical testing and comparison with plasma exchange and IVIG is a laborious and expensive process. Given the low prevalence of PML (three cases in several thousand treated patients), we doubt that anyone will embark voluntarily on this task. However, if natalizumab is to be reapproved, the pharmaceutical company should be obliged by the national drug regulatory authorities to perform these studies. Careful surveillance for PML will be mandatory if natalizumab is reapproved, and a clinical trial of these treatment modalities must be considered if new cases of PML occur in sufficient numbers.