Neonatal murine macrophages show enhanced chemotactic capacity upon toll-like receptor stimulation

New insights into intestinal macrophages in necrotizing enterocolitis: the multi-functional role and promising therapeutic application

Necrotizing enterocolitis (NEC) is an inflammatory intestinal disease that profoundly affects preterm infants. Currently, the pathogenesis of NEC remains controversial, resulting in limited treatment strategies. The preterm infants are thought to be susceptible to gut inflammatory disorders because of their immature immune system. In early life, intestinal macrophages (IMφs), crucial components of innate immunity, demonstrate functional plasticity and diversity in intestinal development, resistance to pathogens, maintenance of the intestinal barrier, and regulation of gut microbiota. When the stimulations of environmental, dietary, and bacterial factors interrupt the homeostatic processes of IMφs, they will lead to intestinal disease, such as NEC. This review focuses on the IMφs related pathogenesis in NEC, discusses the multi-functional roles and relevant molecular mechanisms of IMφs in preterm infants, and explores promising therapeutic application for NEC.

New Insights in Immunometabolism in Neonatal Monocytes and Macrophages in Health and Disease

It is well established that the neonatal immune system is different from the adult immune system. A major task of the neonatal immune system is to bridge the achievement of tolerance towards harmless antigens and commensal bacteria while providing protection against pathogens. This is highly important because neonates are immunologically challenged directly after birth by a rigorous change from a semi-allogeneic sterile environment into a world rich with microbes. A so called disease tolerogenic state is typical for neonates and is anticipated to prevent immunopathological damage potentially at the cost of uncontrolled pathogen proliferation. As a consequence, neonates are more susceptible than adults to life-threatening infections. At the basis of a well-functioning immune response, both for adults and neonates, innate immune cells such as monocytes and monocyte-derived macrophages play an essential role. A well-responsive monocyte will alter its cellular metabolism to subsequently induce certain immune effector function, a process which is called immunometabolism. Immunometabolism has received extensive attention in the last decade; however, it has not been broadly studied in neonates. This review focuses on carbohydrate metabolism in monocytes and macrophages in neonates. We will exhibit pathways involving glycolysis, the tricarboxylic acid (TCA) cycle and oxidative phosphorylation and their role in shaping neonates' immune systems to a favorable tolerogenic state. More insight into these pathways will elucidate potential treatments targets in life-threatening conditions including neonatal sepsis or expose potential targets which can be used to induce tolerance in conditions where tolerance is harmfully impaired such as in autoimmune diseases.

Phenotypic Switch of Human Peritoneal Macrophages during Childhood

INTRODUCTION

 Human peritoneal macrophages are resident in the abdominal cavity where they support the specific microenvironmental regulation. We have previously observed a phenotypic switch of murine macrophages during infancy that was associated with a functional development. To investigate the age related changes in human peritoneal macrophages, we analyzed peritoneal macrophages of children undergoing laparoscopic procedures.

MATERIALS AND METHODS

 Immunologically healthy children who received minimally invasive surgery in our department were included in this study. In all cases, the written consent was obtained. At the beginning of laparoscopy, physiologic NaCl-solution was instilled and manually removed through the umbilical trocar to gain macrophages. Lavage cells were processed for flow cytometry analysis. CD14+ myeloid cells were monitored for specific lineage marker expression.

RESULTS

 A total of 21 donors (age: 7 days-18 years) were included and divided into three groups. In all age groups, 97% of myeloid cells expressed CD11b. 70% of these expressed CD14. Three subsets of CD14 cells were detected on the basis of CD14/CD16 expression (CD14 + CD16dim, CD14 + CD16inter, and CD14 + CD16high). In neonates, >80% belonged to the CD14 + CD16high subset, reducing to 30% in adolescents. In none of the cases, the M2 markers CD23 and CD25 were expressed.

CONCLUSION

 This is the first study showing that lineage marker expression of peritoneal macrophages in neonates differs from that in adults. The knowledge about neonatal tissue resident macrophages might help to understand their complex interaction and to use specific macrophage properties for therapeutic approaches.