Abstract: Gene Reports 26 (2022) 101509 Contents lists available at ScienceDirect Gene Reports journal homepage: www.elsevier.com/locate/genrep Serum levels of vitamin D and immune system function in patients with COVID-19 admitted to intensive care unit Mohammad Sadegh Soltani-Zangbar a, Ata Mahmoodpoor b, Sanam Dolati c, **, Ali Shamekh d, Sepehr Valizadeh d, Mehdi Yousefi a, Sarvin Sanaie e, * a Department of Immunology, School of Medicine, Tabriz University of Medical Sciences, Tabriz, Iran Department of Anesthesiology and Critical Care, Faculty of Medicine, Tabriz University of Medical Sciences, Tabriz, Iran Physical Medicine and Rehabilitation Research Center, Aging Research Institute, Tabriz University of Medical Sciences, Tabriz, Iran d Student Research Committee, Tabriz University of Medical Sciences, Tabriz, Iran e Neurosciences Research Center, Aging Research Institute, Tabriz University of Medical Sciences, Tabriz, Iran b c A R T I C L E I N F O A B S T R A C T Edited by Hee-Jeong Im Sampen Objective: Vitamin D is believed to affect the functionality of the immune system for the prevention of coronavirus disease. To investigate the role of this vitamin against the Coronavirus, this study analyzed the serum levels of vitamin D, the transcription pattern of inflammatory cytokines, and the frequency of total lymphocytes, TCD4+, TCD8+, and NK cells in 50 COVID-19-affected subjects in comparison to 50 healthy participants. Materials and methods: This study diagnosed and evaluated 100 patients. Frequency of lymphocytes was deter­ mined using flow cytometry. Cytokine expression levels were measured using Real-Time PCR. Serum levels of vitamin D and cytokines levels in cultured cell supernatant were measured by ELISA. Results: Patients with COVID-19 exhibited decreased serum levels of vitamin D versus the healthy participants (p = 0.0024). The total number of lymphocytes, TCD4+, TCD8+, and NK cells was significantly reduced in patients with COVID-19 (p < 0.0001). Considerable upregulation of IL-12, IFN-γ, and TNF-α was seen in COVID-19 pa­ tients compared to the control group, whereas IFN-α was downregulated in COVID-19 patients. ELISA results also had increased levels of IL-12, TNF-α, and IFN-γ (p = 0.0014, 0.0012, and p < 0.0001, respectively), and decreased level of IFN-α (p = 0.0021) in patients with COVID-19 compared to the control group. Conclusion: These findings suggest a probable association among vitamin D concentrations, immune system function, and risk of COVID-19 infection. As a result, it is recommended that vitamin D be considered as a candidate for handling and controlling COVID-19 because of its ability to target the cytokine storm and its antiviral effects. Keywords: COVID-19 SARS Coronavirus Vitamin D Immune Response Lymphocytes Cytokines