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.

MS and clinically isolated syndromes: shared specificity but diverging clonal patterns of virus-specific IgG antibodies produced in vivo and by CSF B cells in vitro

BACKGROUND

Intrathecal synthesis of oligoclonal IgG antibodies against measles virus (MeV), varicella zoster virus (VZV) and herpes simplex virus type-1 (HSV-1) is a characteristic feature multiple sclerosis (MS).

METHODS

We have used isoelectric focusing-immunoblot to define the clonal patterns of IgG and of IgG antibodies to MeV, VZV and HSV-1 in supernatants of in vitro cultures of peripheral blood lymphocytes (PBL) and cerebrospinal fluid (CSF) cells and in sera and CSF from three patients with MS and three patients with clinically isolated syndromes (CIS) suspective of demyelinating disease.

RESULTS

In vitro synthesis of IgG by PBL was not detected in any patient. In contrast, in vitro synthesis by CSF cells of oligoclonal IgG and oligoclonal IgG antibodies to one or two of the three viruses tested was observed in all six patients. The clonal patterns of the in vitro synthesized IgG and virus specific IgG differed to varying extent from those synthesized intrathecally in vivo. However, in each patient, the in vitro and in vivo intrathecally produced antibodies displayed specificity for the same viruses. The addition of B cell activating factor (BAFF) had no effect on the amounts or clonal patterns of either total IgG or virus-specific IgG produced by CSF cells in vitro.

CONCLUSION

Virus specific B cells capable of spontaneous IgG synthesis are clonally expanded in the CSF of patients with MS. The B-cell repertoire in CSF samples is only partially representative of the intrathecal B-cell repertoire.

Multiple sclerosis: glatiramer acetate induces anti-inflammatory T cells in the cerebrospinal fluid

Glatiramer acetate (GA) is believed to induce GA-reactive T cells that secrete anti-inflammatory cytokines at the site of inflammation in multiple sclerosis (MS). However, GA-reactive T cells have not been established from the intrathecal compartment of MS patients, and intrathecal T cells may differ from T cells in blood. Here, we compared the phenotype of GA-reactive T cells from the cerebrospinal fluid (CSF) and blood of five MS patients treated with GA for 3-36 months, and in three of these patients also before treatment. From the CSF of these patients, all 22 T cell lines generated before and all 38 T cell lines generated during treatment were GA-reactive. GA treatment induced a more pronounced anti-inflammatory profile of GA-reactive T cell lines from CSF than from blood. While GA-reactive T cell clones from CSF were restricted by either human leukocyte antigen (HLA) -DR or HLA-DP, only HLA-DR restricted GA-reactive T cell clones were detected in blood. No cross reactivity with myelin proteins was detected in GA-reactive T cell lines or clones from CSF. These results suggest that a selected subset of GA-reactive T cells are present in the intrathecal compartment, and support an anti-inflammatory mechanism of action for GA.

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

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.