Elevated Type 2 Inflammatory Factors, Th2/Th1 Balanced Status, and Exosomes as a Marker of Severity in Chronic Actinic Dermatitis.

Background: Chronic actinic dermatitis (CAD) is a skin inflammation triggered by light exposure, occurring at the exposed site and potentially causing widespread inflammation throughout the body. While we hypothesize that severe CAD could progress to atopic dermatitis, the exact inflammatory mechanisms and pathogenesis remain unclear. Objective: We aimed to investigate the relationships between CAD severity and clinical and immunological parameters. Methods: CAD patients were classified into two groups based on severity: mild CAD and severe CAD. We assessed total IgE levels, eosinophil count in peripheral blood (PB), the ratio of Th2 cell percentage to Th1 cell percentages (Th2/Th1), and cytokine/chemokine levels in both PB and skin lesions. Results: In our study, eosinophil counts in patients with severe CAD and mild CAD were significantly higher than those in the control group (p  < 0.05). It was exhibited a higher Th2/Th1 ratio in severe-CAD patients compared with mild-CAD patients and control group (p  < 0.05). There were significant increases in the levels of IL-4, IL-5, IL-8, IL-31, and IFN-γ in the lesions of severe CAD patients compared to the control group (p  < 0.05). Additionally, the level of CD63 exosomes in the PB of severe-CAD patients was significantly elevated compared to the control group (p  < 0.05). Persistent elevations of CD63 exosomes in severe CAD patients were associated with the Th2/Th1 balance status in PB (p  < 0.05). Conclusion: Severe CAD demonstrates a shift toward Th2 immunity from Th2/Th1, accompanied by elevated with inflammatory factors such as IL-4, IL-5, IL-31, IL-8, and IFN-γ in skin lesions, as well as increased CD63 exosomes in PB. Thus, consequently, exosomes and Th2/Th1 imbalance may contribute to the systemic manifestations observed in CAD patients.