Less Neutrophil Extracellular Trap Formation in Term Newborns than in Adults

Abstract

Background: Newborns are prone to infections, which are independent predictors of neonatal mortality and morbidity. Neutrophil extracellular traps (NETs) are structures composed of chromatin and antimicrobial molecules that capture and kill pathogens. NETs may play an important role in the innate immune system and, thus, might be associated with impaired neonatal immune function. Objectives: This study aimed to compare NET formation between term neonates and healthy adults. We additionally investigated the effects of gestational age, birth weight, mode of delivery, gender, and perinatal infections. Methods: We collected cord blood from 57 term infants (mean gestational age, 39.1 weeks) and 9 late preterm infants (35 weeks), and peripheral blood from 18 healthy adult donors. Neutrophils were isolated, and then NET formation was induced using three different stimulants: N-formylmethionine-leucyl-phenylalanine, phorbol 12-myristate 13-acetate (PMA), or lipopolysaccharide. NETs were immunohistochemically stained and analyzed with regard to NET percentage and NET area. Results: With all three stimuli, healthy term infants showed a lower NET percentage than the adult control group (p < 0.0001 each). The groups also differed in NET area, but the significance level was lower. Following PMA stimulation, we observed greater reductions in NET percentage and NET area in preterm than term infants. Conclusions: The lower NET formation observed in term infants compared to adults likely contributes to the reduced neonatal immune response. NET formation appeared to be even further decreased in late preterm neonates. There remains a need for further investigations of NET formation in more immature preterm infants.

Age is the work of art? Impact of neutrophil and organism age on neutrophil extracellular trap formation

“…Thus, neonate neutrophils seem to be sensitive to fungal stimulation but not necessarily the bacterial components (Byrd et al 2016 ). However, in contrast to Lipp et al ( 2017 ), Marcos et al ( 2009 ) showed that neonatal neutrophils can cast NETs upon LPS (as well as other numerous TLR agonists) although at first the signal is weaker (Marcos et al 2009 ). Direct comparison of the two studies indicates that neonate neutrophils release NETs but they require a longer time for their maximal formation.…”

“…3 ). Neutrophils isolated from infants/neonates displayed impaired NET production after stimulation with LPS, PAF and fMLP, in contrast to neutrophils collected from adult individuals (Yost et al 2009 ; Lipp et al 2017 ). This was despite the presence of functional receptors that recognize these molecules and uncompromised phagocytosis.…”

“…Nevertheless, when bacteria ( E. coli , S. aureus ) or PMA were used to induce NETs, neonatal neutrophils did not form NETs (Yost et al 2009 ). On the other hand, Lipp et al ( 2017 ) reported that the cells of term infants release some NETs in response to PMA and those of preterm babies release significantly fewer of these structures. Importantly, the defect of NET formation by neutrophils of preterm and term neonates was not rescued by the ROS donor (glucose oxidase) (Yost et al 2009 ).…”

The emerging role of immunothrombosis in paediatric conditions

“…Ramirez et al (2016) suggested three possible reasons for this: (i) the low threshold of activation of neutrophils, which limits the development of reliable, easy, cheap diagnostic assays; (ii) the high costs of clinical trials; (iii) the lack of identification of appropriate targets to safely inhibit or decrease the NETs' activity without impairing the defence. 6 Neonates are more prone to infection than adults, perhaps due to the lower levels of NETosis exhibited by them, 91 thus having a complete understand of the role of NETs in human disease would assist us in targeting treatment to either group. Currently, this age-dependent difference in NETosis makes it challenging to work on future pharmacological treatments.…”

Age-Appropriate Functions and Dysfunctions of the Neonatal Neutrophil

“…Neonatal neutrophils from term and preterm infants fail to form NETs in this manner, even though they have the ability to generate endogenous ROS and have NADPH activity equivalent to adult cells ( 152 ). Hence, Lipp and coworkers demonstrated significantly less NET formation, with reduced NET area, from neonatal cord blood neutrophils compared to adult cells following stimulation with N -formylmethionine-leucyl-phenylalanine (fMLP), PMA, and LPS, with even lower numbers and NET area noted in preterm neonatal neutrophils ( 153 ). This may be due to NET-inhibitory factors (nNIF) or nHIF-related peptides, which appear to be unique to neonatal neutrophils and function as important regulators of fetal and neonatal inflammation ( 154 ).…”