O04 The effects of solar simulated UVR on human immune system

Abstract Introduction and aims The role of sunlight in dermatology has long been debated. Recent research highlights numerous health benefits of sunlight exposure, including increased longevity and reduced risks of heart disease and cancer, beyond the effects of vitamin D. We hypothesize that solar-simulated ultraviolet (UV) radiation (UVR) can alter gene expression and immune cell function in the peripheral blood of healthy individuals independent of vitamin D. Our study aims to investigate these effects at the single-cell level. Methods We conducted a pilot study involving healthy volunteers in Scotland during winter when background UV levels were at their lowest (UV index < 1). Participants (n = 6) received 2 weeks of artificial UVR exposure. Participants took 100 µg of vitamin D before the start of the study to maintain high plasma vitamin D levels throughout the experiment, thereby eliminating the influence of vitamin D. Peripheral blood samples were collected before and after the intervention. Immune cell populations and T-cell receptor (TCR) repertoire changes were analysed using single-cell RNA sequencing (scRNAseq) and TCR sequencing. Results Following UVR exposure, we observed a slight increase in the proportions of monocytes and dendritic cells, while T-cell subsets showed a relative decline, possibly related to UV-induced changes in T-cell trafficking. Key genes such as GPSM3 and TGFB were significantly downregulated across various cell subsets (Padj < 0.05, log fold change < −1), suggesting potential protective effects of UVR in autoimmune diseases. TCR diversity significantly increased (Shannon Index, P < 0.05), indicating enhanced immune surveillance through a broader T-cell receptor repertoire. Conclusions Our findings provide novel insights into the nonvitamin D effects of UVR on immune function, highlighting its potential to modulate immune cell composition, TCR diversity and gene expression. This research could pave the way for therapeutic strategies that leverage UVR to enhance immune health and prevent disease.