Background: Multiple sclerosis (MS) is characterized by perivascular inflammation and high levels of circulating T and B lymphocytes that respond to the myelin antigens myelin basic protein (MBP) and proteolipid protein (PLP), thereby suggesting a role for immunoregulatory cytokines.
Materials and method: Blood mononuclear cells (MNC) were prepared from patients with MS, optic neuritis (ON), myasthenia gravis (MG), other inflammatory (OIND) and non-inflammatory neurological diseases (OND), and from patients with HIV infection and healthy controls. MNC expressing cytokine mRNA were detected by in situ hybridization with radiolabelled cDNA oligonucleotide probes. Numbers of cytokine mRNA expressing cells were presented per standard numbers of MNC.
Results: MS patients had elevated numbers of MNC in blood expressing T helper type 1 (Th1) cell related interferon-gamma (IFN-gamma), Th2 cell associated interleukin-4 (IL-4) and the endogenously produced immunosuppressant transforming growth factor-beta (TGF-beta). IFN-gamma and TGF-beta correlated with MS disability: EDSS score < 3 was associated with high numbers of TGF-beta mRNA positive cells while IFN-gamma mRNA positive cells tended to be low. The reverse was seen in patients with EDSS > or = 3. Cultures of MNC in presence and absence of antigen revealed that MBP and PLP induced strong responses in MS reflected by high levels of IFN-gamma, IL-4 and TGF-beta mRNA expressing cells. Recombinant (r) TGF-beta 1 dose-dependently suppressed MBP-induced upregulation of the proinflammatory cytokines IFN-gamma, IL-4, IL-6, tumor necrosis factor-alpha, (TNF-alpha), TNF-beta and perforin, but not of the immunosuppressive and probably advantageous IL-10. Cytokine mRNA expressing cells were enriched in the MS patients' cerebrospinal fluid, as were the cytokine mRNA positive cells detected after culture in presence of MBP and PLP, reflecting an autonomy of the immune response in this compartment. ON, in many instances representing early MS, did not differ from clinically definite MS regarding profiles of IFN-gamma, IL-4 and TGF-beta. Also patients with MG had elevated numbers of IFN-gamma, IL-4 and TGF-beta mRNA expressing blood MNC. They were further augmented upon culture of the MG patients' MNC in presence of acetylcholine receptor (AChR). An upregulation of AChR-induced TGF-beta was observed in thymectomized patients. rTGF-beta suppressed AChR-induced upregulation of proinflammatory cytokines but not IL-10. Elevated numbers of IFN-gamma, IL-4 and TGF-beta mRNA expressing blood MNC were also found in patients with OIND (aseptic meningo-encephalitis, chronic inflammatory demyelinating polyneuropathy, polymyositis, Eaton-Lambert syndrome) and in HIV-infected patients. In HIV infection, numbers of IL-4 mRNA positive cells correlated inversely with CD4+ cell counts, reflecting the involvement of IL-4 in later stages of the disease. Patients with non-inflammatory neurological diseases and healthy subjects had either no or low numbers of IFN-gamma, IL-4 and TGF-beta mRNA expressing cells when blood MNC were examined without previous culture, and after culture in presence and absence of MBP, PLP and AChR as antigens. An exception was a healthy pregnant lady who showed high levels especially of IL-4 and IL-10 mRNA expressing cells, probably reflecting pregnancy-associated upregulation of Th2 cell related cytokines. Numbers of myelin antigen- and AChR-reactive IFN-gamma and IL-4 mRNA expressing cells were also elevated, implicating upregulation of natural T cell autoimmunity in normal pregnancy.
Conclusion: High numbers of in vivo activated and of organ-specific antigen-responsive Th1 and Th2 like cells expressing IFN-gamma and IL-4 mRNA are characteristic for MS and MG. Upregulation of TGF-beta in MS patients with little disability and in MG after thymectomy implicates that TGF-beta has desirable effects in human diseases with autoimmune background.