The neonatal liver hosts a spontaneously occurring neutrophil population, exhibiting distinct spatial and functional characteristics from adults.

The elusive nature of the liver immune system in newborns remains an important challenge, casting a shadow over our understanding of how to effectively treat and prevent diseases in children. Therefore, deeper exploration into the intricacies of neonatal immunology might be crucial for improved pediatric healthcare. Using liver intravital microscopy, we unveiled a significant population of granulocytes in the hepatic parenchyma of fetuses and newborns. Utilizing high-dimensional immunophenotyping, we showed dynamic alterations predominantly in granulocytes during neonatal development. Liver intravital microscopy from birth through adulthood captures real-time dynamics, showing a substantial presence of Ly6G + cells that persisted significantly up to 2 weeks of age. Using CyTOF, we characterized neonatal Ly6G + cells as neutrophils, confirmed by morphology and immunohistochemistry. Surprisingly, the embryonic liver hosts a distinct population of neutrophils established as early as the second gestational week, challenging conventional notions about their origin. Additionally, we observed that embryonic neutrophils occupy preferentially the extravascular space, indicating their early establishment within the liver. Hepatic neutrophils in embryos and neonates form unique cell clusters, persisting during the initial days of life, while reduced migratory capabilities in neonates are observed, potentially compensating with increased reactive oxygen species (ROS) release in response to stimuli. Finally, in vivo imaging of acute neutrophil behavior in a newborn mouse, subjected to focal liver necrosis, unveils that neonatal neutrophils exhibit a reduced migratory response. The study provides unprecedented insights into the intricate interplay of neutrophils within the liver, shedding light on their functional and dynamic characteristics during development.

Inhibition of 5-lipoxygenase alleviates graft-versus-host disease.

Leukotriene B4 (LTB4), a proinflammatory mediator produced by the enzyme 5-lipoxygenase (5-LO), is associated with the development of many inflammatory diseases. In this study, we evaluated the participation of the 5-LO/LTB4 axis in graft-versus-host disease (GVHD) pathogenesis by transplanting 5-LO-deficient leukocytes and investigated the effect of pharmacologic 5-LO inhibition by zileuton and LTB4 inhibition by CP-105,696. Mice that received allogeneic transplant showed an increase in nuclear 5-LO expression in splenocytes, indicating enzyme activation after GVHD. Mice receiving 5-LO-deficient cell transplant or zileuton treatment had prolonged survival, reduced GVHD clinical scores, reduced intestinal and liver injury, and decreased levels of serum and hepatic LTB4 These results were associated with inhibition of leukocyte recruitment and decreased production of cytokines and chemokines. Treatment with CP-105,696 achieved similar effects. The chimerism or the beneficial graft-versus-leukemia response remained unaffected. Our data provide evidence that the 5-LO/LTB4 axis orchestrates GVHD development and suggest it could be a target for the development of novel therapeutic strategies for GVHD treatment.

Macrophage migration inhibitory factor drives neutrophil accumulation by facilitating IL-1ß production in a murine model of acute gout.

This study evaluated the role of macrophage migration inhibitory factor in inflammation caused by monosodium urate crystals. The concentration of macrophage migration inhibitory factor was increased in synovial fluid of patients with acute gout, and there was a positive correlation between intra-articular macrophage migration inhibitory factor and IL-1ß concentrations. In mice, the injection of monosodium urate crystals into the knee joint increased the levels of macrophage migration inhibitory factor in macrophages and in inflamed tissue. The injection of recombinant macrophage migration inhibitory factor into the joint of mice reproduced the inflammatory response observed in acute gout, including histologic changes, the recruitment of neutrophils, and increased levels of IL-1ß and CXCL1. Importantly, the accumulation of neutrophils and the amount IL-1ß in the joints were reduced in macrophage migration inhibitory factor-deficient mice when injected with monosodium urate crystals. We observed a similar effect when we blocked macrophage migration inhibitory factor with (S,R)-3-(4-hydroxyphenyl)-4,5-dihydro-5-isoxazole acetic acid or anti-macrophage migration inhibitory factor. In addition, the blockade of IL-1R and CXCR2 reduced recombinant macrophage migration inhibitory factor-induced neutrophil recruitment. Mechanistically, recombinant macrophage migration inhibitory factor is important for the synthesis of il1ß mRNA in vivo and in isolated macrophages. Altogether, macrophage migration inhibitory factor promotes neutrophil accumulation and is important for IL-1ß production, which are 2 crucial events contributing to the pathogenesis of acute gout.

Evaluation of carbon nanotubes functionalized with sodium hyaluronate in the inflammatory processes for oral regenerative medicine applications.

OBJECTIVES: The objectives of this study were to assess the effects of hyaluronic acid (HY), multi-walled carbon nanotubes (MWCNT), and MWCNT functionalized with HY (HY-MWCNT) on the resolution of neutrophilic inflammation in the pleural cavity of LPS-challenged mice and to assess the influence of these materials in the inflammatory process of bone repair of tooth sockets of rats. MATERIALS AND METHODS: C57Bl/6 mice were intra-pleurally injected with HY, MWCNT, HY-MWCNT, phosphate-buffered saline (PBS), or LPS. The animals were euthanized after 8 and 24 h, and cells were harvested for total and differential cell counting. The tooth sockets of Wistar rats were filled with HY, MWCNT, HY-MWCNT, or blood clot (control). After 1, 3, and 7 days, histological and morphometric analyses evaluated the number of cell nuclei and blood vessels, and bone trabeculae formation in the sockets. Myeloperoxidase (MPO) activity quantified neutrophil accumulation in the sockets. RESULTS: HY, MWCNT, and HY-MWCNT increased neutrophilic recruitment at 8 h and reduced the inflammatory process at 24 h in the pleural cavity. Histological and morphometric analyses and MPO activity showed no significant differences in the recruitment of inflammatory cells in the tooth sockets. HY increased the number of blood vessels, and HY and HY-MWCNT increased bone trabeculae formation at 7 days of tooth extraction. CONCLUSIONS: HY, MWCNT, and HY-MWCNT resolved the neutrophilic inflammation in the pleural cavity of the mice. However, these materials did not modulate the inflammatory process in the early stages of bone repair of the tooth sockets, thereby excluding this action as a possible mechanism by which these biomaterials accelerate bone repair. CLINICAL RELEVANCE: HY-MWCNT is capable of accelerating bone repair/regeneration without affecting the inflammatory phase during the bone healing process.

Switching off key signaling survival molecules to switch on the resolution of inflammation.

Inflammation is a physiological response of the immune system to injury or infection but may become chronic. In general, inflammation is self-limiting and resolves by activating a termination program named resolution of inflammation. It has been argued that unresolved inflammation may be the basis of a variety of chronic inflammatory diseases. Resolution of inflammation is an active process that is fine-tuned by the production of proresolving mediators and the shutdown of intracellular signaling molecules associated with cytokine production and leukocyte survival. Apoptosis of leukocytes (especially granulocytes) is a key element in the resolution of inflammation and several signaling molecules are thought to be involved in this process. Here, we explore key signaling molecules and some mediators that are crucial regulators of leukocyte survival in vivo and that may be targeted for therapeutic purposes in the context of chronic inflammatory diseases.