EPIGENETIC SIGNATURES OF SEVERE RSV INFECTION IN INFANTS: EVIDENCE FROM NON-INVASIVE SALIVA SAMPLES

Respiratory syncytial virus (RSV) poses significant morbidity and mortality risks in childhood, particularly among previously healthy infants hospitalized without predisposing risk factors for severe disease. This study aimed to investigate the role of the host epigenome in RSV infection severity using non-invasive buccal swabs from sixteen hospitalized infants. Eight patients exhibited severe symptoms, while eight had mild to moderate symptoms. DNA methylation analysis was performed using the Illumina EPIC BeadChip on DNA isolated from saliva samples. A cohort of healthy children served as controls to assess baseline DNA methylation levels of identified biomarkers. Candidate gene methylation levels were further validated by pyrosequencing in both the discovery and validation cohorts. A panel of differentially methylated positions (DMPs) distinguishing severe from mild to moderate RSV symptoms in infants was identified. DMPs were determined using a threshold of adjusted P-value (false discovery rate, FDR) < 0.01 and an absolute DNA methylation difference (delta beta) > 0.10. Differentially methylated regions (DMRs) were identified in genes implicated in asthma, pulmonary disease, and viral infections. The differential DNA methylation of these genes was validated in an independent replication cohort. A weighted correlation network analysis highlighted the pivotal role of a module with a hub gene crucial in regulating viral infections. Oral mucosa methylation may contribute to RSV disease severity in infants.