Studies on T cells and cytokines in Guillain-Barré syndrome and experimental allergic neuritis

• Guillain-Barrésyndrome (GBS) is an inflammatory disease of peripheral nerves, characterised by muscle weakness. The nerves are attacked and destroyed by the immune system. The symptoms usually progress over a few weeks and many patients become severely disabled. However, in contrast to many other organspecific autoimmune diseases, GBS is self-limiting and most patients recover. Individuals of all ages can be affected. The incidence is about 1/100 000 per year. An infection often precedes the onset of neurological symptoms and probably triggers the immune-mediated attack.Activation of T cells and the resulting release of cytokines are decisive for the regulation of antigen-specific inflammation. Different cytokine patterns promote different types of responses. Interferon-y (lFN-γ) has a key role in Th type 1 responses, and is thought to be a driving force in many organ-specific autoimmune diseases. Interleukin-4 (IL-4) promotes Th type 2 responses, characterised by the production of certain antibodies and activation of mastcells and eosinophils. Th type 1 and Th type 2 responses down-regulate one another and the balance between them is important for the immune homeostasis. TGF-ß is an important cytokine with strong down-regulatory properties.Flow cytometry studies showed that circulating T cells were activated in patients with GBS as determined by expression of HLA-DR on T cells, increased proportion of activated memory phenotype (CD4+CD29+), and decreased proportion of naive phenotype (CD4+CD45RA+). A sensitive Ell-spot method was used to determine cytokine secretion from circulating mononuclear cells with or without stimulation with immunogenic peptides from myelin proteins P2 and PO. Both spontaneous and myelin-specific cytokine secretion were increased in patients compared with controls. Increased numbers of myelin-specific cells secreting IL-4 and TGF-ß were found in the majority of the patients, indicating a Th2 type and down-regulatory cytokine profile, in line with the self-limiting character of the disease.An animal model of GBS, experimental allergic neuritis (EAN), is known to be inducible by myelin-specific T cells, supporting the pathogenetic role of T cells. A Th1 deviated, IFN-y-producing cell population from EAN, was in vitro stimulated with autoantigen and IL-4, thereby obtaining a Th2 cytokine profile. These myelin-specific cells were subsequently transferred to rats with EAN, and were found to ameliorate the disease course.In conclusion, Circulating T cells are activated in patients with GBS. Most patients have myelin-specific T cells that mainly secrete down-regulatory cytokines such as IL-4 and TGF-ß, which probably have a beneficial role in regulating the disease process. In vitro deviation of myelin-specific T cells into Th2 phenotype and subsequent transfer of these cells ameliorated the disease course in EAN.

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