Editorial: Immunity in compromised newborns

The risk of infection-related morbidities and mortality is particularly high in the newborn period. Before birth, the mammalian fetus is protected from adverse effects of exogenous pathogenic microbes and can normally develop its immune system in a near-sterile environment with limited need for immune responses. This condition changes dramatically at birth when rapid adaptations of the innate and adaptive immune systems are required to tolerate and respond to commensal and pathogenic bacteria at epithelial surfaces (e.g. gut, lungs, skin) and fight microbes penetrating to blood and internal organs. Carefully balanced responses of the systemic, organ-related and epithelial immune systems are required to avoid bacterial overgrowth, translocation across immature barriers, and excessive inflammation. The many arms of the mammalian immune system develop differently in different species but comparative studies facilitate insights into mechanisms of perinatal immune development and help identify prophylactic and therapeutic opportunities. Interventions to support neonatal immunity are most critical for those born preterm, growth-restricted, hypoxic, infected or otherwise compromised at birth. This Research Topic presents a collection of 29 original research articles and reviews on perinatal immunology, aimed to understand the special challenges of compromised newborns. The Research Topic collection is connected with the completion of the international NEOMUNE research consortium, led by University of Copenhagen (www.neomune.ku.dk, 2013-20), having a focus on milk and microbiota influences on gut, immunity and brain development. The Research Topic and this editorial combine knowledge obtained in the NEOMUNE consortium with a series of complementary articles. We encourage studies into the mechanisms of systemic and mucosal immune development, and how dietary, microbial and pharmacological interventions support immune maturation assessed by both classical immune markers and exploratory omics techniques. The latter methods have recently emerged as novel tools to better understand immune development and prepare the way for a new precision medicine approach to the prevention, diagnosis and treatment of neonatal immune disorders (1, 2)