Cord blood antimicrobial peptide LL37 levels in preterm neonates and association with preterm complications

Antimicrobial Peptides (AMPs) and the Microbiome in Preterm Infants: Consequences and Opportunities for Future Therapeutics

Antimicrobial peptides (AMPs) are crucial components of the innate immune system in various organisms, including humans. Beyond their direct antimicrobial effects, AMPs play essential roles in various physiological processes. They induce angiogenesis, promote wound healing, modulate immune responses, and serve as chemoattractants for immune cells. AMPs regulate the microbiome and combat microbial infections on the skin, lungs, and gastrointestinal tract. Produced in response to microbial signals, AMPs help maintain a balanced microbial community and provide a first line of defense against infection. In preterm infants, alterations in microbiome composition have been linked to various health outcomes, including sepsis, necrotizing enterocolitis, atopic dermatitis, and respiratory infections. Dysbiosis, or an imbalance in the microbiome, can alter AMP profiles and potentially lead to inflammation-mediated diseases such as chronic lung disease and obesity. In the following review, we summarize what is known about the vital role of AMPs as multifunctional peptides in protecting newborn infants against infections and modulating the microbiome and immune response. Understanding their roles in preterm infants and high-risk populations offers the potential for innovative approaches to disease prevention and treatment.

Nasal cathelicidin is expressed in early life and is increased during mild, but not severe respiratory syncytial virus infection

Respiratory syncytial virus is the major cause of acute lower respiratory tract infections in young children, causing extensive mortality and morbidity globally, with limited therapeutic or preventative options. Cathelicidins are innate immune antimicrobial host defence peptides and have antiviral activity against RSV. However, upper respiratory tract cathelicidin expression and the relationship with host and environment factors in early life, are unknown. Infant cohorts were analysed to characterise early life nasal cathelicidin levels, revealing low expression levels in the first week of life, with increased levels at 9 months which are comparable to 2-year-olds and healthy adults. No impact of prematurity on nasal cathelicidin expression was observed, nor were there effects of sex or birth mode, however, nasal cathelicidin expression was lower in the first week-of-life in winter births. Nasal cathelicidin levels were positively associated with specific inflammatory markers and demonstrated to be associated with microbial community composition. Importantly, levels of nasal cathelicidin expression were elevated in infants with mild RSV infection, but, in contrast, were not upregulated in infants hospitalised with severe RSV infection. These data suggest important relationships between nasal cathelicidin, upper airway microbiota, inflammation, and immunity against RSV infection, with interventional potential.

Antimicrobial peptide LL37 and regulatory T cell associated with late-onset sepsis in very preterm infants

Stem cell therapy may prevent late-onset sepsis (LOS) via antimicrobial peptide LL37 secretion and regulatory T cell (Treg) regulation. The early prediction of LOS is still a challenge. This study evaluated whether immunological state of LL37 or Tregs precedes LOS. We firstly analyzed the LL37 level, Treg proportion, and LOS incidence in very preterm infants treated with autologous cord blood mononuclear cells (ACBMNCs) in our previous trial. Then, we constructed a prediction model and built validation cohort. We found ACBMNC intervention reduced the incidence of LOS from 27.3% to 6.9% (p = 0.021). LL37 and Treg abundances were higher in the ACBMNCs group. The nomogram demonstrated that early-life Treg and LL37 characteristics were closely associated with LOS (area under the curve, AUC 0.936), with implications for early prediction and timely clinical management. This composite model was also helpful to evaluate the beneficial effect of ACBMNCs intervention on LOS, thus promoting translational research.