Maternal plasma level of antimicrobial peptide LL37 is a major determinant factor of neonatal plasma LL37 level.

To determine cathelicidin antimicrobial peptide LL37subcellular distribution in cord neutrophils and normal plasma LL37 levels in mothers and neonates, relate them to delivery mode and relevant biochemical markers, including 25-OHvitamin D [25(OH)D] as this molecules increases cathelicidin gene expression. A total of 115 infants were included, n = 68 with normal delivery and n = 47 with elective Caesarean section (C-section), a subset of these being 50 mother-infant pairs. Biomarkers were determined in maternal and cord blood. Subcellular peptide LL37 distribution was analysed with immunoelectron microscopy. Cord plasma LL37 levels were three-times higher after normal delivery compared with C-section. A highly significant correlation was observed between maternal and cord plasma LL37 levels, regardless of delivery mode. No relationship was found between LL37 and 25(OH)D levels. Neutrophils from cord blood after normal delivery contained 10-times more cytoplasmatic cathelicidin peptide compared with corresponding cells after C-section where a strict granular localization was found. These data are consistent with a placental transfer of LL37 and identifies maternal stores as the critical factor determining neonatal plasma LL37 level. An additional enhancement of neonatal cathelicidin mobilization and release is connected to normal delivery stress.