Preterm infants are highly susceptible to late-onset
sepsis (LOS) and
necrotizing enterocolitis (NEC), but disease pathogenesis and specific diagnostic markers are lacking. Circulating
cell-free DNA (
cfDNA) and immune cell-derived
proteins are involved in multiple
immune diseases in adults but have not been investigated in preterm neonates. We explored the relation of circulating neutrophil-associated
proteins and
cfDNA to LOS and/or NEC. Using a clinically relevant preterm pig model of spontaneous LOS and NEC development, we investigated neutrophil-associated
proteins and
cfDNA in plasma, together with
cytokines in gut tissues. The changes in
cfDNA levels were further studied in preterm pigs and neonatal mice with induced
sepsis, and in preterm infants with or without LOS and/or NEC. Fifteen of 114 preterm pigs spontaneously developed both LOS and NEC, and they showed increased intestinal levels of
IL-6 and IL-1β and plasma levels of
cfDNA, neutrophil-associated
proteins, and
proteins involved in platelet-neutrophil interaction during systemic
inflammation. The abundance of neutrophil-associated
proteins highly correlated with
cfDNA levels. Further, Staphylococcus epidermidis challenge of neonatal mice and preterm pigs increased plasma
cfDNA levels and bacterial accumulation in the spleen. In infants, plasma
cfDNA levels were elevated at LOS diagnosis and 1-6 d before NEC. In conclusion, elevated levels of plasma
cfDNA and neutrophil
proteins are associated with LOS and NEC diagnosis.