IL-24 in COVID-19 Patients: Correlations with Disease Progression

Interleukin-24 (IL-24) is a cytokine known for its role in immune regulation and apoptosis, with potential implications in viral infections like COVID-19. This study aimed to investigate the association between IL-24 serum levels and the severity of COVID-19 disease. In this prospective bi-center cross-sectional study, we enrolled 41 COVID-19 patients from two hospitals in Germany. Serial blood samples were collected from a subset of patients, resulting in 88 total blood samples. Patients were categorized into critical, severe, moderate, and mild disease groups based on WHO criteria. IL-24 serum levels were measured during the acute or convalescent phase using an ELISA assay. Inflammatory markers, and kidney and liver function parameters were also evaluated. Statistical analysis included non-parametric tests and correlation analysis. Elevated IL-24 serum levels were observed in ambulant patients (mild disease), compared to hospitalized patients (critical, severe, moderate disease, <i>p</i> < 0.05). IL-24 levels were also significantly higher in patients without oxygenation disorder compared to those with oxygenation therapy (<i>p</i> < 0.05). A negative correlation was found between IL-24 levels and markers of inflammation and liver/kidney function. Elevated IL-24 serum levels were associated with milder COVID-19 courses, suggesting a protective role in modulating immune responses and promoting antiviral apoptosis. Conversely, reduced IL-24 in severe cases may reflect impaired immune regulation, highlighting its potential as a biomarker and therapeutic target.