Cytokine expression in response to bacterial antigens in preterm and term infant cord blood monocytes

Background: Neonatal susceptibility to bacterial infection is associated with an immature immune system, but the role of different bacterial antigens in specific responses is largely unknown. Objective: To evaluate differences in intracellular cytokine response to physiologically relevant bacterial antigens in term and preterm infants as compared with adults. Methods: Cord blood samples from preterm and term neonates and adult peripheral blood samples were cultured ex vivo with and without whole heat-killed bacteria. Intracellular leukocyte production of interleukin (IL)-6, IL-10, IL-12, and IL-8 responses was assessed by flow cytometry. Results: Monocytes were the primary producers of all mediators. Escherichia coli was the most potent stimulant. Lactobacillus plantarum299v activated fewer monocytes as compared with E. coli for all responses (p < 0.05), except for IL-12 in term neonates. IL-6 response to Staphylococcus epidermidis was lower in both groups of neonates as compared with adults (p = 0.023 and p = 0.001). IL-8 response to S. epidermidis was lower in term as compared with preterm neonates and adults (p = 0.003). IL-10 response to group B streptococci was lower in term neonates as compared with adults and higher in preterm as compared with term neonates (p = 0.015). Conclusions: Monocytes from term neonates compared to preterm neonates show a downregulated anti-inflammatory response to specific bacteria. High neonatal response to pathogenic E. coli in the preterm infant could cause uncontrolled inflammatory response, while lower IL-6 response to S. epidermidis in neonates may indicate a basis for vulnerability to S. epidermidis infection.