Composition of early life leukocyte populations in preterm infants with and without late-onset sepsis

Impact of Extreme Prematurity, Chorioamnionitis, and Sepsis on Neonatal Monocyte Characteristics and Functions

INTRODUCTION

The innate branch of the immune system is important in early life, in particular for infants born preterm.

METHODS

We performed a longitudinal analysis of the peripheral monocyte compartment in extremely preterm children from a randomized, placebo-controlled study of probiotic supplementation. PBMCs and fecal samples were collected at several timepoints during the first months of life. Monocyte characteristics were analyzed by flow cytometry, and LPS-stimulated PBMC culture supernatants were analyzed by Luminex or ELISA. Plasma cytokines and gut microbiota composition were analyzed by ELISA and 16S rRNA-sequencing, respectively.

RESULTS

The extremely preterm infants had persistent alterations in their monocyte characteristics that were further aggravated in chorioamnionitis cases. They showed a markedly reduced TLR4 expression and hampered LPS-stimulated cytokine responses 14 days after birth. Notably, at later timepoints, TLR4 expression and LPS responses no longer correlated. Sepsis during the first weeks of life strongly associated with increased pro-inflammatory, and reduced IL-10, responses also at postmenstrual week 36. Further, we report a correlation between gut microbiota features and monocyte phenotype and responses, but also that probiotic supplementation associated with distinct monocyte phenotypic characteristics, without significantly influencing their responsiveness.

CONCLUSION

Extremely preterm infants have monocyte characteristics and functional features that deviate from infants born full-term. Some of these differences persist until they reach an age corresponding to full-term, potentially making them more vulnerable to microbial exposures during the first months of life.

Early-life risk factors which govern pro-allergic immunity

Allergic diseases affect up to 40% of the global population with a substantial rise in food allergies, in particular, over the past decades. For the majority of individuals with allergy fundamental programming of a pro-allergic immune system largely occurs in early childhood where it is crucially governed by prenatal genetic and environmental factors, including their interactions. These factors include several genetic aberrations, such as filaggrin loss-of-function mutations, early exposure to respiratory syncytial virus, and various chemicals such as plasticizers, as well as the influence of the gut microbiome and numerous lifestyle circumstances. The effects of such a wide range of factors on allergic responses to an array of potential allergens is complex and the severity of these responses in a clinical setting are subsequently not easy to predict at the present time. However, some parameters which condition a pro-allergic immune response, including severe anaphylaxis, are becoming clearer. This review summarises what we currently know, and don't know, about the factors which influence developing pro-allergic immunity particularly during the early-life perinatal period.

Identifying immune signatures of sepsis to increase diagnostic accuracy in very preterm babies

Bacterial infections are a major cause of mortality in preterm babies, yet our understanding of early-life disease-associated immune dysregulation remains limited. Here, we combine multi-parameter flow cytometry, single-cell RNA sequencing and plasma analysis to longitudinally profile blood from very preterm babies (<32 weeks gestation) across episodes of invasive bacterial infection (sepsis). We identify a dynamically changing blood immune signature of sepsis, including lymphopenia, reduced dendritic cell frequencies and myeloid cell HLA-DR expression, which characterizes sepsis even when the common clinical marker of inflammation, C-reactive protein, is not elevated. Furthermore, single-cell RNA sequencing identifies upregulation of amphiregulin in leukocyte populations during sepsis, which we validate as a plasma analyte that correlates with clinical signs of disease, even when C-reactive protein is normal. This study provides insights into immune pathways associated with early-life sepsis and identifies immune analytes as potential diagnostic adjuncts to standard tests to guide targeted antibiotic prescribing.

Meta-analysis of the role of neutrophil to lymphocyte ratio in neonatal sepsis

INTRODUCTION

The neutrophil to lymphocyte ratio (NLR), an inflammatory biomarker, measures innate-adaptive immune system balance. In this systematic review and meta-analysis, we aim to analyze the current literature to evaluate the diagnostic role of NLR in neonatal sepsis.

METHODS

PubMed, Web of Science, and Scopus were used to conduct a systematic search for relevant publications published before May 14, 2022.

RESULTS

Thirty studies, including 2328 neonates with sepsis and 1800 neonates in the control group, were included in our meta-analysis. The results indicated that NLR is higher in neonates with sepsis compared to healthy controls (SMD = 1.81, 95% CI = 1.14-2.48, P-value < 0.001) in either prospective (SMD = 2.38, 95% CI = 1.40-3.35, P-value < 0.001) or retrospective studies (SMD = 0.87, 95% CI = 0.63-1.12, P-value < 0.001) with a pooled sensitivity of 79% (95% CI = 62-90%), and a pooled specificity of 91% (95% CI = 73-97%). Also, we found that NLR is higher in neonates with sepsis compared to those who were suspected of sepsis but eventually had negative blood cultures (SMD =1.99, 95% CI = 0.76-3.22, P-value = 0.002) with a pooled sensitivity of 0.79% (95% CI = 0.69-0.86%), and a pooled specificity of 73% (95% CI = 54-85%). In addition, neonates with sepsis had elevated levels of NLR compared to other ICU admitted neonates (SMD = 0.73, 95% CI = 0.63-0.84, P < 0.001). The pooled sensitivity was 0.65 (95% CI, 0.55-0.80), and the pooled specificity was 0.80 (95% CI, 0.68-0.88).

CONCLUSION

Our findings support NLR as a promising biomarker that can be readily integrated into clinical settings to aid in diagnosing neonatal sepsis. As evidenced by our results, restoring balance to the innate and adaptive immune system may serve as attractive therapeutic targets. Theoretically, a reduction in NLR values could be used to measure therapeutic efficacy, reflecting the restoration of balance within these systems.