{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,3,25]],"date-time":"2026-03-25T07:56:38Z","timestamp":1774425398959,"version":"3.50.1"},"reference-count":36,"publisher":"MDPI AG","issue":"6","license":[{"start":{"date-parts":[[2026,3,23]],"date-time":"2026-03-23T00:00:00Z","timestamp":1774224000000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/501100004412","name":"Turkish Academy of Sciences","doi-asserted-by":"crossref","id":[{"id":"10.13039\/501100004412","id-type":"DOI","asserted-by":"crossref"}]},{"name":"Presidency of Turkish Health Institutes","award":["TB-22906"],"award-info":[{"award-number":["TB-22906"]}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["IJMS"],"abstract":"<jats:p>Multiple sclerosis is a chronic immune-mediated central nervous system disorder marked by neuroinflammation, demyelination, and neurodegeneration, and effectively modeled by experimental autoimmune encephalomyelitis. The objective of this study was to elucidate the roles of T follicular helper and T follicular regulatory cells in the progression of experimental autoimmune encephalomyelitis and to assess their association with IL-21 expression and central nervous system tissue pathology. In this study, experimental autoimmune encephalomyelitis was induced in 25 adult female C57BL\/6 mice. Fluorescent double immunostaining for CXCR5 in combination with PD-1, ICOS, CD4, and FOXP3 was performed, along with the analysis of IL-21 mRNA expression. Histopathological assessment was conducted on the cerebrum, cerebellum, and medulla spinalis to evaluate neuroinflammation and myelin loss. A significant increase in CXCR5+PD-1+ and CXCR5+ICOS+ T follicular helper-like cells was observed in brain tissue, indicating immune activation and T follicular helper cell involvement. Simultaneously, a marked decrease in FOXP3+ T follicular regulatory-like cells suggested impaired immune tolerance and enhanced autoimmune activity. The infiltration of T follicular helper-like cells was identified as a key driver of inflammation and demyelination in the central nervous system. Additionally, the elevated IL-21 mRNA expression highlighted B cell activation and the initiation of antibody-mediated responses. These findings suggest that dysregulation of the T follicular helper\/T follicular regulatory axis and elevated IL-21 expression contribute to the immunopathogenesis of experimental autoimmune encephalomyelitis, providing further insight into the mechanisms underlying multiple sclerosis development.<\/jats:p>","DOI":"10.3390\/ijms27062901","type":"journal-article","created":{"date-parts":[[2026,3,23]],"date-time":"2026-03-23T13:07:06Z","timestamp":1774271226000},"page":"2901","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["Impaired T Follicular Regulatory Cell Function and Enhanced T Follicular Helper Cell Activity in Experimental Autoimmune Encephalomyelitis: Mechanistic Insights into CNS Autoimmunity"],"prefix":"10.3390","volume":"27","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-5027-6756","authenticated-orcid":false,"given":"Gulam","family":"Hekimoglu","sequence":"first","affiliation":[{"name":"Department of Histology and Embryology, Hamidiye International Faculty of Medicine, University of Health Sciences, Istanbul 34668, Turkey"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-8250-8227","authenticated-orcid":false,"given":"Kubra","family":"Sevgin","sequence":"additional","affiliation":[{"name":"Department of Histology and Embryology, Hamidiye International Faculty of Medicine, University of Health Sciences, Istanbul 34668, Turkey"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-2689-4287","authenticated-orcid":false,"given":"Nurullah","family":"Yucel","sequence":"additional","affiliation":[{"name":"Department of Anatomy, Hamidiye Faculty of Medicine, University of Health Sciences, Istanbul 34668, Turkey"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-3375-8956","authenticated-orcid":false,"given":"Gamze","family":"Yesilay","sequence":"additional","affiliation":[{"name":"Department of Molecular Biology and Genetics, Hamidiye Institute of Health Sciences, University of Health Sciences, Istanbul 34668, Turkey"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0009-0006-6939-4054","authenticated-orcid":false,"given":"Salime Pelin","family":"Erguven","sequence":"additional","affiliation":[{"name":"Department of Histology and Embryology, Hamidiye International Faculty of Medicine, University of Health Sciences, Istanbul 34668, Turkey"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-6852-3030","authenticated-orcid":false,"given":"Muzaffer","family":"Seker","sequence":"additional","affiliation":[{"name":"Turkish Academy of Sciences, Ankara 06690, Turkey"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2026,3,23]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"61","DOI":"10.1016\/j.neuron.2006.09.011","article-title":"The neurobiology of multiple sclerosis: Genes, inflammation, and neurodegeneration","volume":"52","author":"Hauser","year":"2006","journal-title":"Neuron"},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"1622","DOI":"10.1016\/S0140-6736(18)30481-1","article-title":"Multiple sclerosis","volume":"391","author":"Thompson","year":"2018","journal-title":"Lancet"},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"1021","DOI":"10.1002\/jnr.24224","article-title":"Animal models of multiple sclerosis: Focus on experimental autoimmune encephalomyelitis","volume":"96","author":"Bjelobaba","year":"2018","journal-title":"J. Neurosci. Res."},{"key":"ref_4","doi-asserted-by":"crossref","first-page":"4587","DOI":"10.1007\/s00415-020-10275-x","article-title":"Contributions of T cells in multiple sclerosis: What do we currently know?","volume":"268","author":"Arneth","year":"2021","journal-title":"J. Neurol."},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"696","DOI":"10.1038\/s41590-018-0135-x","article-title":"Reassessing B cell contributions in multiple sclerosis","volume":"19","author":"Li","year":"2018","journal-title":"Nat. Immunol."},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"771","DOI":"10.1111\/joim.13215","article-title":"Current and emerging disease-modulatory therapies and treatment targets for multiple sclerosis","volume":"289","author":"Piehl","year":"2021","journal-title":"J. Intern. Med."},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"621","DOI":"10.1146\/annurev-immunol-031210-101400","article-title":"Follicular helper CD4 T cells (TFH)","volume":"29","author":"Crotty","year":"2011","journal-title":"Annu. Rev. Immunol."},{"key":"ref_8","doi-asserted-by":"crossref","unstructured":"Guo, J., Zhao, C., Wu, F., Tao, L., Zhang, C., Zhao, D., Yang, S., Jiang, D., Wang, J., and Sun, Y. (2018). T follicular helper-like cells are involved in the pathogenesis of experimental autoimmune encephalomyelitis. Front. Immunol., 9.","DOI":"10.3389\/fimmu.2018.00944"},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"247","DOI":"10.1038\/s41467-019-14118-w","article-title":"Integrated single cell analysis of blood and cerebrospinal fluid leukocytes in multiple sclerosis","volume":"11","author":"Schafflick","year":"2020","journal-title":"Nat. Commun."},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"410","DOI":"10.1016\/j.it.2015.05.005","article-title":"T follicular regulatory cells in the regulation of B cell responses","volume":"36","author":"Sage","year":"2015","journal-title":"Trends Immunol."},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"832","DOI":"10.4049\/jimmunol.1500759","article-title":"Circulating follicular regulatory T cells are defective in multiple sclerosis","volume":"195","author":"Dhaeze","year":"2015","journal-title":"J. Immunol."},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"71","DOI":"10.1080\/08916934.2017.1284821","article-title":"Transcriptional and epigenetic regulation of follicular T-helper cells and their role in autoimmunity","volume":"50","author":"Qiu","year":"2017","journal-title":"Autoimmunity"},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"274","DOI":"10.3109\/1547691X.2015.1089343","article-title":"IL-21 and IL-21 receptor in the immunopathogenesis of multiple sclerosis","volume":"13","author":"Ghalamfarsa","year":"2016","journal-title":"J. Immunotoxicol."},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"210","DOI":"10.1111\/j.1750-3639.2007.00064.x","article-title":"The immunopathology of multiple sclerosis: An overview","volume":"17","author":"Lassmann","year":"2007","journal-title":"Brain Pathol."},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"219","DOI":"10.1111\/j.1600-065X.2010.00923.x","article-title":"The PD-1 pathway in tolerance and autoimmunity","volume":"236","author":"Francisco","year":"2010","journal-title":"Immunol. Rev."},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"153","DOI":"10.1002\/wsbm.1187","article-title":"The role of regulatory T cells in neurodegenerative diseases","volume":"5","author":"He","year":"2013","journal-title":"Wiley Interdiscip. Rev. Syst. Biol. Med."},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"932","DOI":"10.1016\/j.immuni.2011.03.023","article-title":"ICOS receptor instructs T follicular helper cell versus effector cell differentiation by inducing differential expression of transcription factors","volume":"34","author":"Choi","year":"2011","journal-title":"Immunity"},{"key":"ref_18","doi-asserted-by":"crossref","first-page":"1132","DOI":"10.1016\/j.immuni.2019.04.011","article-title":"T follicular helper cell biology: A decade of discovery and diseases","volume":"50","author":"Crotty","year":"2019","journal-title":"Immunity"},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"485","DOI":"10.1146\/annurev.immunol.021908.132710","article-title":"IL-17 and Th17 cells","volume":"27","author":"Korn","year":"2007","journal-title":"Annu. Rev. Immunol."},{"key":"ref_20","doi-asserted-by":"crossref","first-page":"3750","DOI":"10.4049\/jimmunol.181.6.3750","article-title":"Cutting edge: Th1 cells facilitate the entry of Th17 cells to the central nervous system during experimental autoimmune encephalomyelitis","volume":"181","author":"Prendergast","year":"2008","journal-title":"J. Immunol."},{"key":"ref_21","doi-asserted-by":"crossref","first-page":"102619","DOI":"10.1016\/j.jaut.2021.102619","article-title":"Regulatory T cells in autoimmune hepatitis: An updated overview","volume":"119","author":"Longhi","year":"2021","journal-title":"J. Autoimmun."},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"1535","DOI":"10.1084\/jem.20080159","article-title":"IL-12- and IL-23-modulated T cells induce distinct types of EAE based on histology, CNS chemokine profile, and response to cytokine inhibition","volume":"205","author":"Kroenke","year":"2008","journal-title":"J. Exp. Med."},{"key":"ref_23","doi-asserted-by":"crossref","first-page":"393","DOI":"10.1038\/nri2550","article-title":"Autoimmune T cell responses in the central nervous system","volume":"9","author":"Goverman","year":"2009","journal-title":"Nat. Rev. Immunol."},{"key":"ref_24","doi-asserted-by":"crossref","first-page":"1","DOI":"10.1111\/j.1365-2249.2010.04143.x","article-title":"CD4+ T cells in multiple sclerosis and experimental autoimmune encephalomyelitis","volume":"162","author":"Fletcher","year":"2010","journal-title":"Clin. Exp. Immunol."},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"9041","DOI":"10.1073\/pnas.0802218105","article-title":"IL-6 blockade inhibits the induction of myelin antigen-specific Th17 cells and Th1 cells in experimental autoimmune encephalomyelitis","volume":"105","author":"Serada","year":"2008","journal-title":"Proc. Natl. Acad. Sci. USA"},{"key":"ref_26","doi-asserted-by":"crossref","first-page":"233","DOI":"10.1084\/jem.20041257","article-title":"IL-23 drives a pathogenic T cell population that induces autoimmune inflammation","volume":"201","author":"Langrish","year":"2005","journal-title":"J. Exp. Med."},{"key":"ref_27","doi-asserted-by":"crossref","first-page":"183","DOI":"10.4103\/2319-4170.155590","article-title":"T cell mediated pathogenesis in EAE: Molecular mechanisms","volume":"38","author":"Kurschus","year":"2015","journal-title":"Biomed. J."},{"key":"ref_28","doi-asserted-by":"crossref","first-page":"7867","DOI":"10.4049\/jimmunol.175.12.7867","article-title":"IL-21 induces differentiation of human naive and memory B cells into antibody-secreting plasma cells","volume":"175","author":"Ettinger","year":"2005","journal-title":"J. Immunol."},{"key":"ref_29","doi-asserted-by":"crossref","first-page":"986","DOI":"10.1016\/j.immuni.2011.10.015","article-title":"Th17 cells induce ectopic lymphoid follicles in central nervous system tissue inflammation","volume":"35","author":"Peters","year":"2011","journal-title":"Immunity"},{"key":"ref_30","doi-asserted-by":"crossref","first-page":"959","DOI":"10.1038\/ni.2649","article-title":"Antiapoptotic Mcl-1 is critical for the survival and niche-filling capacity of Foxp3+ regulatory T cells","volume":"14","author":"Pierson","year":"2013","journal-title":"Nat. Immunol."},{"key":"ref_31","doi-asserted-by":"crossref","first-page":"484","DOI":"10.1038\/nature05970","article-title":"IL-21 initiates an alternative pathway to induce proinflammatory T(H)17 cells","volume":"448","author":"Korn","year":"2007","journal-title":"Nature"},{"key":"ref_32","doi-asserted-by":"crossref","first-page":"353","DOI":"10.1084\/jem.20091738","article-title":"IL-21 acts directly on B cells to regulate Bcl-6 expression and germinal center responses","volume":"207","author":"Linterman","year":"2010","journal-title":"J. Exp. Med."},{"key":"ref_33","first-page":"2075","article-title":"The inflamed central nervous system drives the activation and rapid proliferation of Foxp3+ regulatory T cells","volume":"184","author":"Malpass","year":"2010","journal-title":"J. Immunol."},{"key":"ref_34","doi-asserted-by":"crossref","first-page":"577730","DOI":"10.1016\/j.jneuroim.2021.577730","article-title":"Weight bearing as a measure of disease progression in experimental autoimmune encephalomyelitis","volume":"361","author":"Segal","year":"2021","journal-title":"J. Neuroimmunol."},{"key":"ref_35","first-page":"e51275","article-title":"Myelin oligodendrocyte glycoprotein (MOG35-55) induced experimental autoimmune encephalomyelitis (EAE) in C57BL\/6 mice","volume":"86","author":"Bittner","year":"2014","journal-title":"J. Vis. Exp."},{"key":"ref_36","first-page":"465","article-title":"Histopathological parameters of the spinal cord in different phases of experimental autoimmune encephalomyelitis","volume":"74","author":"Fosciak","year":"2023","journal-title":"J. Physiol. Pharmacol."}],"container-title":["International Journal of Molecular Sciences"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/1422-0067\/27\/6\/2901\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2026,3,25]],"date-time":"2026-03-25T06:10:02Z","timestamp":1774419002000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/1422-0067\/27\/6\/2901"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2026,3,23]]},"references-count":36,"journal-issue":{"issue":"6","published-online":{"date-parts":[[2026,3]]}},"alternative-id":["ijms27062901"],"URL":"https:\/\/doi.org\/10.3390\/ijms27062901","relation":{},"ISSN":["1422-0067"],"issn-type":[{"value":"1422-0067","type":"electronic"}],"subject":[],"published":{"date-parts":[[2026,3,23]]}}}