en Radiation Biology Radiation Biology تحقيق بديع Original Research <div style="text-align: justify;"><span style="font-size:10pt"><span style="text-justify:newspaper"><span style="text-kashida-space:50%"><span style="line-height:119%"><span style="font-family:Calibri"><span style="color:black"><span lang="en-US" style="font-size:9.0pt"><span style="font-family:Calibri"><span style="color:#1f497d"><span style="font-style:italic"><span style="font-weight:bold"><span style="language:en-US">Background:</span></span></span></span></span></span> <span lang="en-US" style="font-size:9.0pt"><span style="font-family:Calibri"><span style="language:en-US">Experimental autoimmune myositis (EAM) is characterized by immune-mediated skeletal muscle inflammation. Imbalance between Th17 and regulatory T (Treg) cells contributes to disease pathogenesis. MicroRNA-21 (miR-21) has been implicated in immune regulation and radiation responses, yet its role in EAM remains unclear. This study aimed to investigate the expression of miR-21 following local radiation in a murine EAM model and to assess its correlation with Th17/Treg immune imbalance. </span></span></span><span lang="en-US" style="font-size:9.0pt"><span style="font-family:Calibri"><span style="color:#1f497d"><span style="font-style:italic"><span style="font-weight:bold"><span style="language:en-US">Materials and Methods: </span></span></span></span></span></span><span lang="en-US" style="font-size:9.0pt"><span style="font-family:Calibri"><span style="language:en-US">Female C57BL/6 mice were induced with EAM and randomized into control and radiation groups. Local hindlimb irradiation (15 Gy) was administered to the radiation group. Muscle tissues and draining lymph nodes were collected at day 28 post-induction. Flow cytometry quantified Th17 (CD4⁺IL-17A⁺) and Treg (CD4⁺FoxP3⁺) populations. Quantitative real-time PCR measured miR-21 expression in muscle samples. Correlations between miR-21 levels and Th17/Treg ratios were analyzed. </span></span></span><span lang="en-US" style="font-size:9.0pt"><span style="font-family:Calibri"><span style="color:#1f497d"><span style="font-style:italic"><span style="font-weight:bold"><span style="language:en-US">Results: </span></span></span></span></span></span><span lang="en-US" style="font-size:9.0pt"><span style="font-family:Calibri"><span style="language:en-US">Radiation significantly reduced muscle inflammation and improved histopathological scores compared to non-irradiated EAM mice (p<0.05). Th17 frequencies decreased while Treg frequencies increased following irradiation (p<0.01). miR-21 expression was significantly downregulated in irradiated muscle tissues (p<0.01). Notably, miR-21 levels showed a positive correlation with Th17/Treg ratios (r=0.68, p<0.01). </span></span></span><span lang="en-US" style="font-size:9.0pt"><span style="font-family:Calibri"><span style="color:#1f497d"><span style="font-style:italic"><span style="font-weight:bold"><span style="language:en-US">Conclusion: </span></span></span></span></span></span><span lang="en-US" style="font-size:9.0pt"><span style="font-family:Calibri"><span style="language:en-US">Local radiation modulates immune responses in EAM by downregulating miR-21 and restoring Th17/Treg balance, suggesting a potential therapeutic mechanism involving miR-21-mediated immune regulation.</span></span></span></span></span></span></span></span></span></div> Experimental autoimmune myositis, miR-21, Th17 cells, regulatory T-cells, immune imbalance, radiation. 585 590 http://ijrr.com/browse.php?a_code=A-10-1-1544&slc_lang=en&sid=1 L. Wang 7900319475328460034085 7900319475328460034085 No Department of Neurology, Ningbo No.2 Hospital, Ningbo 315000, China Q. Ye 7900319475328460034086 7900319475328460034086 No Department of Pulmonology, Ningbo No.2 Hospital, Ningbo 315000, China W. Yan Yw961804121@163.com 7900319475328460034087 7900319475328460034087 Yes Department of Neurology, Ningbo No.2 Hospital, Ningbo 315000, China