Adaptation to existence outside the womb is a key event in the life of a mammal. The absence of macrophages in rats with a homozygous mutation in the colony-stimulating factor 1 receptor (Csf1r) gene (Csf1rko) severely compromises pre-weaning somatic growth and maturation of organ function. Transfer of wild-type bone marrow cells (BMT) at weaning rescues tissue macrophage populations permitting normal development and long-term survival. To dissect the phenotype and function of macrophages in postnatal development, we generated transcriptomic profiles of all major organs of wild-type and Csf1rko rats at weaning and in selected organs following rescue by BMT. The transcriptomic profiles revealed subtle effects of macrophage deficiency on development of all major organs. Network analysis revealed a common signature of CSF1R-dependent resident tissue macrophages that includes the components of complement C1Q (C1qa/b/c genes). Circulating C1Q was almost undetectable in Csf1rko rats and rapidly restored to normal levels following BMT. Tissue-specific macrophage signatures were also identified, notably including sinus macrophage populations in the lymph nodes. Their loss in Csf1rko rats was confirmed by immunohistochemical localisation of CD209B (SIGNR1). By 6-12 weeks, Csf1rko rats succumb to emphysema-like pathology associated with the selective loss of interstitial macrophages and granulocytosis. This pathology was reversed by BMT. Along with physiological rescue, BMT precisely regenerated the abundance and expression profiles of resident macrophages. The exception was the brain, where BM-derived microglia-like cells had a distinct expression profile compared to resident microglia. In addition, the transferred BM failed to restore blood monocyte or CSF1R-positive bone marrow progenitors. These studies provide a model for the pathology and treatment of CSF1R mutations in humans and the innate immune deficiency associated with prematurity.
Copyright: © 2025 Carter-Cusack et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

ABSTRACT Immune cells in the pancreas are known to participate in organ development. However, the resident pancreatic immune system has yet to be fully defined. Immune cells also play a role in pathology and are implicated in diseases such as diabetes induced by intrauterine growth restriction (IUGR). We hypothesized that the resident immune system is established during neonatal development and disrupted by IUGR. Using single cell RNAseq and flow cytometry we identified many immune cell populations in the near-term fetus (at embryologic day 22) and neonatal (postnatal day 1, 7, &14) islets, non-endocrine pancreas, and the spleen in the rat. Using flow cytometry, we observed the resident immune system is established during neonatal development in the pancreas and spleen. We identified 9 distinct immune populations in the pancreatic islets and 8 distinct immune populations in the spleen by single cell RNAseq. There were no sex-specific differences in the relative proportion of immune cells in the pancreas or spleen. Finally, we tested if IUGR disrupted the neonatal immune system using bilateral uterine artery ligation. We found significant changes to the percentage of CD11B+ HIS48- and CD8+ T cells in the islets and non-endocrine pancreas and in the spleen. IUGR-induced alterations were influenced by the tissue environment and the sex of the offspring. Future research to define the role of these immune cells in pancreatic development may identify disrupted pathways that contribute to the development of diabetes following IUGR.

Bacteria adapt to selective pressure in their immediate environment in multiple ways. One mechanism involves the acquisition of independent mutations that disable or modify a key pathway, providing a signature of adaptation via convergent evolution. Extra-intestinal pathogenic Escherichia coli (ExPEC) belonging to sequence type 95 (ST95) represent a global clone frequently associated with severe human infections including acute pyelonephritis, sepsis, and neonatal meningitis. Here, we analysed a publicly available dataset of 613 ST95 genomes and identified a series of loss-of-function mutations that disrupt cellulose production or its modification in 55.3% of strains. We show the inability to produce cellulose significantly enhances ST95 invasive infection in a rat model of neonatal meningitis, leading to the disruption of intestinal barrier integrity in newborn pups and enhanced dissemination to the liver, spleen and brain. Consistent with these observations, disruption of cellulose production in ST95 augmented innate immune signalling and tissue neutrophil infiltration in a mouse model of urinary tract infection. Mutations that disrupt cellulose production were also identified in other virulent ExPEC STs, Shigella and Salmonella, suggesting a correlative association with many Enterobacteriaceae that cause severe human infection. Together, our findings provide an explanation for the emergence of hypervirulent Enterobacteriaceae clones.
© 2024. The Author(s).

Oxidative stress and fibrosis are important stress responses that characterize bronchopulmonary dysplasia (BPD), a disease for which only a therapy but not a cure has been developed. In this work, we investigated the effects of mesenchymal stromal cells-derived extracellular vesicles (MSC-EVs) on lung and brain compartment in an animal model of hyperoxia-induced BPD. Rat pups were intratracheally injected with MSC-EVs produced by human umbilical cord-derived MSC, following the Good Manufacturing Practice-grade (GMP-grade). After evaluating biodistribution of labelled MSC-EVs in rat pups left in normoxia and hyperoxia, oxidative stress and fibrosis investigation were performed. Oxidative stress protection by MSC-EVs treatment was proved both in lung and in brain. The lung epithelial compartment ameliorated glycosaminoglycan and surfactant protein expression in MSC-EVs-injected rat pups compared to untreated animals. Pups under hyperoxia exhibited a fibrotic phenotype in lungs shown by increased collagen deposition and also expression of profibrotic genes. Both parameters were reduced by treatment with MSC-EVs. We established an in vitro model of fibrosis and another of oxidative stress, and we proved that MSC-EVs suppressed the induction of αSMA, influencing collagen deposition and protecting from the oxidative stress. In conclusion, intratracheal administration of clinical-grade MSC-EVs protect from oxidative stress, improves pulmonary epithelial function, and counteracts the development of fibrosis. In the future, MSC-EVs could represent a new cure to prevent the development of BPD.
© The Author(s) 2023. Published by Oxford University Press.

Annexin A1 (AnxA1) is highly secreted by neutrophils and binds to formyl peptide receptors (FPRs) to trigger anti-inflammatory effects and efferocytosis. AnxA1 is also expressed in the tumor microenvironment, being mainly attributed to cancer cells. As recruited neutrophils are player cells at the tumor sites, the role of neutrophil-derived AnxA1 in lung melanoma metastasis was investigated here. Melanoma cells and neutrophils expressing AnxA1 were detected in biopsies from primary melanoma patients, which also presented higher levels of serum AnxA1 and augmented neutrophil-lymphocyte ratio (NLR) in the blood. Lung melanoma metastatic mice (C57BL/6; i.v. injected B16F10 cells) showed neutrophilia, elevated AnxA1 serum levels, and higher labeling for AnxA1 in neutrophils than in tumor cells at the lungs with metastasis. Peritoneal neutrophils collected from naïve mice were co-cultured with B16F10 cells or employed to obtain neutrophil-conditioned medium (NCM; 18 h incubation). B16F10 cells co-cultured with neutrophils or with NCM presented higher invasion, which was abolished if B16F10 cells were previously incubated with FPR antagonists or co-cultured with AnxA1 knockout (AnxA1-/-) neutrophils. The depletion of peripheral neutrophils during lung melanoma metastasis development (anti-Gr1; i.p. every 48 h for 21 days) reduced the number of metastases and AnxA1 serum levels in mice. Our findings show that AnxA1 secreted by neutrophils favors melanoma metastasis evolution via FPR pathways, addressing AnxA1 as a potential biomarker for the detection or progression of melanoma.