Self-extinguishing relay waves enable homeostatic control of human neutrophil swarming

Lipid mediators in neutrophil biology: inflammation, resolution and beyond

PURPOSE OF REVIEW

Acute inflammation is the body's first defense in response to pathogens or injury. Failure to efficiently resolve the inflammatory insult can severely affect tissue homeostasis, leading to chronic inflammation. Neutrophils play a pivotal role in eradicating infectious pathogens, orchestrating the initiation and resolution of acute inflammation, and maintaining physiological functions. The resolution of inflammation is a highly orchestrated biochemical process, partially modulated by a novel class of endogenous lipid mediators known as specialized pro-resolving mediators (SPMs). SPMs mediate their potent bioactions via activating specific cell-surface G protein-coupled receptors (GPCR).

RECENT FINDINGS

This review focuses on recent advances in understanding the multifaceted functions of SPMs, detailing their roles in expediting neutrophil apoptosis, promoting clearance by macrophages, regulating their excessive infiltration at inflammation sites, orchestrating bone marrow deployment, also enhances neutrophil phagocytosis and tissue repair mechanisms under both physiological and pathological conditions. We also focus on the novel role of SPMs in regulating bone marrow neutrophil functions, differentiation, and highlight open questions about SPMs' functions in neutrophil heterogeneity.

SUMMARY

SPMs play a pivotal role in mitigating excessive neutrophil infiltration and hyperactivity within pathological milieus, notably in conditions such as sepsis, cardiovascular disease, ischemic events, and cancer. This significant function highlights SPMs as promising therapeutic agents in the management of both acute and chronic inflammatory disorders.

A LTB4/CD11b self-amplifying loop drives pyogranuloma formation in chronic granulomatous disease

Sterile pyogranulomas and heightened cytokine production are hyperinflammatory hallmarks of Chronic Granulomatous Disease (CGD). Using peritoneal cells of zymosan-treated CGD (gp91phox-/-) versus wild-type (WT) mice, an ex vivo system of pyogranuloma formation was developed to determine factors involved in and consequences of recruitment of neutrophils and monocyte-derived macrophages (MoMacs). Whereas WT cells failed to aggregate, CGD cells formed aggregates containing neutrophils initially, and MoMacs recruited secondarily. LTB4 was key, as antagonizing BLT1 blocked neutrophil aggregation, but acted only indirectly on MoMac recruitment. LTB4 upregulated CD11b expression on CGD neutrophils, and the absence/blockade of CD11b inhibited LTB4 production and cell aggregation. Neutrophil-dependent MoMac recruitment was independent of MoMac Nox2 status, BLT1, CCR1, CCR2, CCR5, CXCR2, and CXCR6. As proof of concept, CD11b-deficient CGD mice developed disrupted pyogranulomas with poorly organized neutrophils and diminished recruitment of MoMacs. Importantly, the disruption of cell aggregation and pyogranuloma formation markedly reduced proinflammatory cytokine production.

Quantification of collective signalling in time-lapse microscopy images

Live-cell imaging of fluorescent biosensors has demonstrated that space-time correlations in signalling of cell collectives play an important organisational role in morphogenesis, wound healing, regeneration, and maintaining epithelial homeostasis. Here, we demonstrate how to quantify one such phenomenon, namely apoptosis-induced ERK activity waves in the MCF10A epithelium. We present a protocol that starts from raw time-lapse fluorescence microscopy images and, through a sequence of image manipulations, ends with ARCOS, our computational method to detect and quantify collective signalling. We also describe the same workflow in the interactive napari image viewer to quantify collective phenomena for users without prior programming experience. Our approach can be applied to space-time correlations in cells, cell collectives, or communities of multicellular organisms, in 2D and 3D geometries.

Arp2/3 complex and the pentose phosphate pathway regulate late phases of neutrophil swarming

Neutrophil swarming is an essential process of the neutrophil response to many pathological conditions. Resultant neutrophil accumulations are hallmarks of acute tissue inflammation and infection, but little is known about their dynamic regulation. Technical limitations to spatiotemporally resolve individual cells in dense neutrophil clusters and manipulate these clusters in situ have hampered recent progress. We here adapted an in vitro swarming-on-a-chip platform for the use with confocal laser-scanning microscopy to unravel the complexity of single-cell responses during neutrophil crowding. Confocal sectioning allowed the live visualization of subcellular components, including mitochondria, cell membranes, cortical actin, and phagocytic cups, inside neutrophil clusters. Based on this experimental setup, we identify that chemical inhibition of the Arp2/3 complex causes cell death in crowding neutrophils. By visualizing spatiotemporal patterns of reactive oxygen species (ROS) production in developing neutrophil swarms, we further demonstrate a regulatory role of the metabolic pentose phosphate pathway for ROS production and neutrophil cluster growth.

Neutrophil swarming: Is a good offense the best defense?

The phenomenon of swarming has long been observed in nature as a strategic event that serves as a good offense toward prey and predators. Imaging studies have uncovered that neutrophils employ this swarm-like tactic within infected and inflamed tissues as part of the innate immune response. Much of our understanding of neutrophil swarming builds from observations during sterile inflammation and various bacterial, fungal, and parasitic infections of the skin. However, the architecture and function of the skin differ significantly from vital organs where highly specialized microenvironments carry out critical functions. Therefore, the detrimental extent this perturbation may have on organ function remains unclear. In this review, we examine organ-specific swarming within the skin, liver, and lungs, with a detailed focus on swarming within microvascular environments. In addition, we examine potential "swarmulants" that initiate both transient and persistent swarms that have been implicated in disease.