Vitamin D May Increase the Number of CD4-CD8+ NKT-like Cells in Humans—A Novel Insight into Potential Immunomodulatory Action

<b>Background:</b> Vitamin D has a significant role in immune system regulation due to its profound impact on various immune cells, including Natural Killer T-like (NKT-like) cells. While previous studies have explored the effects of vitamin D on the overall NKT-like cell population, detailed investigations into its impact on specific NKT-like subpopulations are lacking. This study aimed to analyze the correlation between vitamin D levels and NKT-like cell subpopulations (CD4+CD8+; CD4-CD8+; CD4+CD8-; CD4-CD8-) in peripheral blood collected from patients without diseases that can influence vitamin D and/or calcium levels. <b>Methods:</b> Peripheral blood mononuclear cells (PBMCs) were isolated from 86 patients. NKT-like cells were separated from PBMCs using a CD3+ CD56+ NKT cell isolation kit and a magnetic bead separator. Flow cytometry (FC) was applied in order to evaluate the distribution of NKT-like cell subpopulations. <b>Results:</b> A significant positive correlation between vitamin D levels and the CD4-CD8+ NKT-like cell population, particularly the CD4-CD8high subtype was found. Importantly, this correlation was independent of calcium levels, emphasizing the unique impact of vitamin D on CD4-CD8+ NKT-like cells. <b>Conclusions:</b> Our findings suggest that vitamin D concentrations may influence the distribution of NKT-like cell subpopulations in peripheral blood, although further evidence is necessary to confirm this observation. These novel results provide a foundation for elucidating the mechanism underlying the effect of vitamin D on the immune system and may contribute to future therapeutic strategies targeting CD4-CD8+ NKT-like cells in immune and oncological disorders.