Targeted proteomics in late-onset neonatal sepsis: an exploratory analysis

Late-onset neonatal sepsis (LONS) is a major cause of morbidity and mortality in preterm infants, but early diagnosis remains difficult. We aimed to identify candidate proteomic biomarkers of LONS and evaluate whether these changes could be reproduced by in vitro stimulation. Longitudinal blood samples were collected from preterm neonates with suspected LONS and non-septic controls in two neonatal intensive care units, at onset and after 24 and 48 hours. In parallel, whole blood from preterm neonates without LONS was stimulated in vitro with E. coli and S. epidermidis . Protein expression was quantified using targeted proteomics. Fifteen neonates with LONS, eight controls, and ten in vitro stimulation samples were included. Sixty-six proteins showed altered expression during LONS. Upregulated proteins were predominantly cytokines and chemokines, whereas downregulated proteins were associated with development, growth, and metabolism. Most alterations normalized within 48 hours. In vitro stimulation reproduced expression changes for a subset of proteins, suggesting direct pathogen-induced immune responses. LONS in preterm neonates is associated with dynamic proteomic alterations. Combined clinical and in vitro analyses identified biologically relevant candidate biomarkers that may support future diagnostic and monitoring strategies. Further validation in larger, independent cohorts is required before clinical use. Late-onset neonatal sepsis in preterm neonates is associated with pronounced and dynamic changes in protein expression patterns. Targeted proteomics identified candidate biomarkers related to inflammatory signaling, growth, and metabolic pathways. Longitudinal analyses demonstrated rapid normalization of many proteins within 48 hours after sepsis onset. In vitro stimulation distinguished proteins directly induced by pathogen exposure from secondary systemic responses. The identified proteins may serve as targets for future research into diagnostic and monitoring biomarkers for neonatal sepsis in preterm infants.