IMMUNOLOGY OF MULTIPLE SCLEROSIS: A COMPREHENSIVE OVERVIEW OF CELLULAR, MOLECULAR, AND NEUROIMMUNE MECHANISMS

ISSN: 2181-3906 2025 International scientific journal «MODERN SCIENCE АND RESEARCH» VOLUME 4 / ISSUE 12 / UIF:8.2 / MODERNSCIENCE.UZ 628 IMMUNOLOGY OF MULTIPLE SCLEROSIS: A COMPREHENSIVE OVERVIEW OF CELLULAR, MOLECULAR, AND NEUROIMMUNE MECHANISMS Yoqubov Ilyosbek Yaxyobek o`g`li Andijan State Medical institute. Master`s student https://doi.org/10.5281/zenodo.17983522 Abstract. Multiple sclerosis (MS) is a chronic immune-mediated disorder of the central nervous system (CNS) characterized by inflammatory demyelination, axonal injury, and progressive neurodegeneration [1–4]. Although historically regarded as a T cell–driven disease, accumulating evidence demonstrates that MS arises from complex interactions between adaptive and innate immune systems, genetic susceptibility, and environmental exposures [5,10]. Aberrant activation of autoreactive lymphocytes, dysregulated cytokine signaling, breakdown of immune tolerance, and sustained microglial activation collectively drive CNS pathology [1,18–20]. This review provides an in-depth and updated analysis of the immunological mechanisms underlying MS pathogenesis, with particular emphasis on immune tolerance failure, lymphocyte trafficking, antigen presentation, neuroimmune crosstalk, and chronic inflammatory neurodegeneration. Keywords: Multiple sclerosis; Neuroimmunology; Central nervous system autoimmunity; Adaptive immune response; Innate immunity; T lymphocytes; B cells; Microglial activation; Blood–brain barrier dysfunction; Cytokine and chemokine networks; Demyelination; Neurodegeneration; Immune tolerance failure; Antigen presentation; Immunopathogenesis. 1. Introduction: MS as a Prototypical Neuroimmunological Disease Multiple sclerosis represents one of the most extensively studied immune-mediated neurological disorders and serves as a paradigm for CNS autoimmunity [4,31]. Affecting over 2.8 million individuals worldwide, MS typically manifests in early adulthood and leads to cumulative neurological disability [2,4]. The disease course may be relapsing–remitting or progressive, reflecting distinct immunopathological mechanisms [1,20,26]. Advances in immunology have reshaped MS from a purely inflammatory demyelinating disorder to a neuroimmune disease in which inflammation, neurodegeneration, and failed repair coexist [1,10,26]. Understanding the immunological basis of MS is essential not only for diagnostic and therapeutic advances but also for elucidating broader principles of immunemediated CNS disease [5]. 2. Breakdown of Immune Tolerance to CNS Antigens Central to MS pathogenesis is the loss of immune tolerance toward self-antigens expressed within the CNS [6,10]. Under physiological conditions, autoreactive lymphocytes are eliminated or functionally silenced through central and peripheral tolerance mechanisms. In MS, these mechanisms fail, allowing pathogenic immune responses to develop [6,9]. 2.1 Central and Peripheral Tolerance Failure  Central tolerance: Imperfect deletion of autoreactive T cells in the thymus allows lowaffinity myelin-reactive T cells to enter the periphery [6,10].  Peripheral tolerance: Defective regulatory T cell (Treg) function and altered antigen presentation permit autoreactive cell activation [9,10]. Table 1. Major Myelin Autoantigens and Their Immunological Role ISSN: 2181-3906 2025 International scientific journal «MODERN SCIENCE АND RESEARCH» VOLUME 4 / ISSUE 12 / UIF:8.2 / MODERNSCIENCE.UZ 629 Autoantigen Cellular source Pathogenic relevance Myelin basic protein (MBP) Oligodendrocytes CD4⁺ T-cell activation [6,9] Proteolipid protein (PLP) Myelin sheath Epitope spreading [6] Myelin oligodendrocyte glycoprotein (MOG) Outer myelin surface Antibody-mediated injury [14,16] Genetic susceptibility, particularly HLA-DRB1*15:01, strongly influences antigen presentation, while environmental factors such as Epstein–Barr virus infection further skew immune responses toward autoimmunity [2,4,10]. 3. Adaptive Immunity: Central Drivers of MS Pathogenesis 3.1 CD4⁺ T Helper Cells CD4⁺ T cells orchestrate the immune response in MS by recognizing myelin antigens presented by antigen-presenting cells (APCs) [6,9]. Pathogenic differentiation pathways  Th1 cells: Promote macrophage and microglial activation via IFN-γ [6,9]  Th17 cells: Enhance BBB permeability and neutrophil recruitment [7,8,21] Table 2. Functional Roles of CD4⁺ T-cell Subsets Subset Key cytokines Contribution to MS Th1 IFN-γ, TNF-α CNS inflammation [6,9] Th17 IL-17, IL-21 BBB disruption [7,8,21] Treg IL-10, TGF-β Suppressed function in MS [9,10] Th17 cells are particularly implicated in early lesion formation due to their ability to breach the BBB and sustain inflammation [7,21]. 3.2 CD8⁺ T Cells and Neuroaxonal Damage Unlike CD4⁺ cells, CD8⁺ T lymphocytes directly target neurons and oligodendrocytes. Histopathological studies show CD8⁺ cells outnumber CD4⁺ cells in active MS lesions [11,12]. Mechanisms of injury:  Perforinand granzyme-mediated cytotoxicity [11,12]  MHC class I–restricted recognition of CNS cells [13] CD8⁺ T-cell density correlates strongly with irreversible axonal loss and disability progression [12,27]. 4. B Cells and Humoral Immune Dysregulation B cells are now recognized as central contributors to MS pathogenesis beyond antibody production [5,14,16]. 4.1 Pathogenic Functions of B Cells  Antigen presentation to autoreactive T cells [14,16]  Secretion of pro-inflammatory cytokines (IL-6, GM-CSF) [14]  Formation of ectopic lymphoid follicles in meninges [17] Table 3. Immunological Evidence for B-cell Involvement ISSN: 2181-3906 2025 International scientific journal «MODERN SCIENCE АND RESEARCH» VOLUME 4 / ISSUE 12 / UIF:8.2 / MODERNSCIENCE.UZ 630 Observation Significance CSF oligoclonal IgG bands Intrathecal antibody synthesis [14,16] Meningeal B-cell follicles Cortical demyelination [17] Anti-CD20 therapy efficacy Causal pathogenic role [15,28] B-cell depletion therapies have profoundly altered MS treatment paradigms, highlighting the immunological importance of B cells [15,28]. 5. Innate Immunity: Microglia and Macrophages Microglia act as resident immune cells of the CNS and play a dual role in MS [18,19]. Microglial polarization  M1 phenotype: Pro-inflammatory, neurotoxic [18,20]  M2 phenotype: Anti-inflammatory, reparative [19] Table 4. Microglial Functional States in MS Phenotype Mediators Effect M1 ROS, IL-1β, TNF-α Demyelination [18,20] M2 IL-10, growth factors Remyelination [19] Chronic M1 dominance contributes to progressive neurodegeneration [20,26]. 6. Cytokine and Chemokine Networks MS lesions are characterized by a highly organized cytokine milieu [10,21]. Table 5. Key Cytokines Driving MS Immunopathology Cytokine Cellular source Pathogenic effect IL-17 Th17 cells BBB damage [7,21,23] IFN-γ Th1 cells Microglial activation [6,9] TNF-α Macrophages Oligodendrocyte apoptosis [20] IL-10 Treg cells Protective (reduced in MS) [9,10] Chemokines such as CXCL13 facilitate sustained lymphocyte recruitment into the CNS [22]. 7. Blood–Brain Barrier Dysfunction and Immune Cell Trafficking BBB breakdown is a prerequisite for CNS immune infiltration [24,25]. Pathophysiological scheme (textual): Peripheral immune activation → endothelial adhesion molecule upregulation (VCAM-1, ICAM-1) [24] → lymphocyte diapedesis → CNS antigen re-encounter → inflammatory amplification → demyelination and axonal injury [25] 8. Chronic Inflammation and Neurodegeneration Neurodegeneration in MS is not solely a consequence of inflammation but is driven by mitochondrial dysfunction, oxidative stress, iron accumulation, and glutamate-mediated ISSN: 2181-3906 2025 International scientific journal «MODERN SCIENCE АND RESEARCH» VOLUME 4 / ISSUE 12 / UIF:8.2 / MODERNSCIENCE.UZ 631 excitotoxicity [20,26,27]. Chronic microglial activation sustains inflammation even in progressive disease stages [18,26]. 9. Immunological Basis of Disease-Modifying Therapies Table 6. Immunological Targets of MS Therapies Therapy Immune target Mechanism Interferon-β Cytokine balance Immune modulation [3,28] Anti-CD20 mAbs B cells Depletion [15,28] S1P modulators Lymphocyte trafficking CNS isolation [29] Natalizumab α4-integrin BBB migration blockade [30] Therapeutic success underscores the central role of immune dysregulation in MS [3,5]. 10. Conclusion Multiple sclerosis is a multifactorial neuroimmune disorder in which immune tolerance failure, adaptive and innate immune activation, and chronic neuroinflammation converge to drive CNS pathology [1,4,26]. The evolving immunological understanding of MS has transformed therapeutic strategies and continues to inform the development of precision immunotherapies aimed at neuroprotection and remyelination [5,28]. REFERENCES 1. Lassmann H. Pathogenic mechanisms associated with different clinical courses of multiple sclerosis. Front Immunol. 2019;10:3116. 2. Filippi M, Bar-Or A, Piehl F, et al. Multiple sclerosis. Nat Rev Dis Primers. 2018;4:43. 3. Hauser SL, Cree BAC. Treatment of multiple sclerosis: A review. Am J Med. 2020;133(12):1380–1390. 4. Thompson AJ, Baranzini SE, Geurts J, Hemmer B, Ciccarelli O. Multiple sclerosis. Lancet. 2018;391(10130):1622–1636. 5. Bar-Or A, Li R. Cellular immunology of relapsing multiple sclerosis: interactions, immune regulation, and therapeutic interventions. Lancet Neurol. 2021;20(3):225–238. 6. Goverman J. Autoimmune T cell responses in the central nervous system. Nat Rev Immunol. 2009;9:393–407. 7. Kebir H, et al. Preferential recruitment of Th17 cells to the CNS via CCR6–CCL20 axis. Nat Med. 2007;13:1173–1179. 8. Korn T, Bettelli E, Oukka M, Kuchroo VK. IL-17 and Th17 cells. Annu Rev Immunol. 2009;27:485–517. 9. Fletcher JM, Lalor SJ, Sweeney CM, Tubridy N, Mills KHG. T cells in multiple sclerosis. Clin Exp Immunol. 2010;162:1–11. 10. Dendrou CA, Fugger L, Friese MA. Immunopathology of multiple sclerosis. Nat Rev Immunol. 2015;15:545–558. 11. Babbe H, et al. Clonal expansions of CD8⁺ T cells dominate the T cell infiltrate in MS lesions. J Exp Med. 2000;192:393–404. 12. Friese MA, Fugger L. Autoreactive CD8⁺ T cells in MS. Brain. 2009;132:173–185. 13. Zozulya AL, Wiendl H. The role of CD8 T cells in MS. Nat Rev Neurol. 2008;4: 354–365. ISSN: 2181-3906 2025 International scientific journal «MODERN SCIENCE АND RESEARCH» VOLUME 4 / ISSUE 12 / UIF:8.2 / MODERNSCIENCE.UZ 632 14. Bar-Or A, et al. Abnormal B-cell cytokine responses in MS. Brain. 2010;133:174–188. 15. Hauser SL, et al. B-cell depletion with rituximab in relapsing MS. N Engl J Med. 2008;358:676–688. 16. Baker D, et al. B cells in MS: targets and mechanisms. Brain. 2017;140: 290–308. 17. Magliozzi R, et al. Meningeal B-cell follicles in secondary progressive MS. Brain. 2007;130:1089–1104. 18. Prinz M, Priller J. Microglia and brain macrophages in MS. Nat Rev Neurosci. 2014;15:300– 312. 19. Voet S, Prinz M, van Loo G. Microglia in CNS inflammation. Nat Rev Neurol. 2019;15: 593–605. 20. Lassmann H, van Horssen J, Mahad D. Progressive MS pathology. Nat Rev Neurol. 2012;8:647–656. 21. Murphy AC, Lalor SJ, Lynch MA, Mills KHG. Infiltration of Th17 cells in MS. J Neuroimmunol. 2010;225:35–39. 22. Kothur K, et al. CXCL13 in neuroinflammation. J Neuroinflammation. 2016;13:93. 23. Croxford AL, Kurschus FC, Waisman A. IL-17-driven autoimmunity. Front Immunol. 2015;6: 130. 24. Engelhardt B, Ransohoff RM. Capture, crawl, cross: BBB immune surveillance. Trends Immunol. 2012;33:579–589. 25. Alvarez JI, et al. The blood–brain barrier in MS. Cold Spring Harb Perspect Med. 2015;5:a020537. 26. Mahad DH, Trapp BD, Lassmann H. Pathological mechanisms in progressive MS. Lancet Neurol. 2015;14:183–193. 27. Frischer JM, et al. The relation between inflammation and neurodegeneration in MS. Brain. 2009;132:1175–1189. 28. Hemmer B, Kerschensteiner M, Korn T. Role of B cells in MS therapy. Nat Rev Neurol. 2015;11:613–625. 29. Cohen JA, et al. S1P receptor modulators in MS. Lancet Neurol. 2019;18: 1026–1037. 30. Miller DH, et al. Natalizumab mechanisms of action. N Engl J Med. 2003;348:15–23. 31. Compston A, Coles A. Multiple sclerosis. Lancet. 2008;372:1502–1517. 32. Reich DS, Lucchinetti CF, Calabresi PA. MS imaging and pathology. N Engl J Med. 2018;378:169–180.