Immunological Mechanisms and Natalizumab Treatment in Multiple Sclerosis Studies on lymphocytes, inflammatory markers and magnetic resonance spectroscopy

Sammanfattning: Background: Multiple sclerosis (MS) is a chronic inflammatory, demyelinating disease of the central nervous system (CNS), and a frequent cause of neurological disability among young adults. In addition to focal inflammatory demyelinated lesions, diffuse white matter pathology as well as a neurodegenerative component with accumulating axonal damage and gliosis have been demonstrated and contribute to MS disease characteristics. The inflammatory component is considered autoimmune and mediated by auto-reactive T lymphocytes together with other cell populations of the immune system and their respective products like cytokines and chemokines. Treatment with natalizumab, a monoclonal antibody directed against the ?4?1-integrin (VLA-4), reduces migration of potential disease-promoting cells to the CNS. The efficacy of natalizumab in reducing relapses and MRI activity is evident, however associated effects on the immune response and the neurodegenerative component in MS are not clear.Methods: In total 72 MS patients were included, distributed among paper I-IV. We investigated effects associated with one-year natalizumab treatment in 31 MS patients regarding cytokine and chemokine levels in CSF and blood using multiplex bead assay analyses (paper I), as well as treatment effects on blood lymphocyte composition in 40 patients using flow cytometry, including functional assays of lymphocyte activation (paper II). Normal appearing white matter (NAWM) metabolite concentrations were assessed with proton magnetic resonance spectroscopy (1H-MRS) in 27 MS patients before and after one year of treatment (paper III). We also evaluated the balance between circulating T helper (Th) subsets in 33 MS patients using gene expression analyses of the CD4+ T cell related transcription factors in whole blood (paper IV).Results: One-year natalizumab treatment was associated with a marked decline in pro-inflammatory cytokines (IL-1? and IL-6) and chemokines (CXCL8, CXCL9, CXCL10 and CXCL11) intrathecally. Circulating plasma levels of some cytokines (GM-CSF, TNF, IL-6 and IL-10) also decreased after treatment. Natalizumab treatment was further associated with an increase in lymphocyte numbers of major populations in blood (total lymphocytes, T cells, T helper cells, cytotoxic T cells, NK cells and B cells). In addition, T cell responsiveness to recall antigens and mitogens was restored after treatment. As to 1H-MRS metabolite concentrations in NAWM, no change in levels were detected post-to pretreatment on a group level. However, correlation analyses between one-year change in metabolite levels (total creatine and total choline) and levels of pro-inflammatory IL-1? and CXCL8 showed a pattern of high magnitude correlation coefficients (r=0.43-0.67). Gene expression analyses demonstrated a systemically reduced expression of transcription factors related to immunoregulatory T cell populations (regulatory T cells and Th2) in relapsing MS compared with controls.Conclusions: Our findings support that an important mode of action of natalizumab is reducing lymphocyte extravasation, although cell-signalling effects through VLA-4 also may be operative. Correlation analyses between changes 1H-MRS metabolite concentrations and inflammatory markers possibly point towards an association between intrathecal inflammation and gliosis development in NAWM. Finally, gene expression analyses indicate a systemic defect at the mRNA level in relapsing MS, involving downregulation of beneficial CD4+ phenotypes.