Immunity: Neutrophil Quorum at the Wound

Neutrophils versus Protozoan Parasites: Plasmodium, Trichomonas, Leishmania, Trypanosoma, and Entameoba

Neutrophils are the most abundant polymorphonuclear granular leukocytes in human blood and are an essential part of the innate immune system. Neutrophils are efficient cells that eliminate pathogenic bacteria and fungi, but their role in dealing with protozoan parasitic infections remains controversial. At sites of protozoan parasite infections, a large number of infiltrating neutrophils is observed, suggesting that neutrophils are important cells for controlling the infection. Yet, in most cases, there is also a strong inflammatory response that can provoke tissue damage. Diseases like malaria, trichomoniasis, leishmaniasis, Chagas disease, and amoebiasis affect millions of people globally. In this review, we summarize these protozoan diseases and describe the novel view on how neutrophils are involved in protection from these parasites. Also, we present recent evidence that neutrophils play a double role in these infections participating both in control of the parasite and in the pathogenesis of the disease.

Effect of RpoS on the survival, induction, resuscitation, morphology, and gene expression of viable but non-culturable Salmonella Enteritidis in powdered infant formula

Involvement of the transcriptional regulator RpoS in the persistence of viable but non-culturable (VBNC) state has been demonstrated in several species of bacteria. This study investigated the role of the RpoS in the formation and resuscitation of VBNC state in Salmonella enterica serovar Enteritidis CICC 21482 by measuring bacterial survival, morphology, physiological characteristics, and gene expression in wild-type (WT) and rpoS-deletion (ΔrpoS) strains during long-term storage in powdered infant formula (PIF). The ΔrpoS strain was produced by allelic exchange using a suicide plasmid. Bacteria were inoculated into PIF for 635-day storage. Survival, morphology, intracellular reactive oxygen species (ROS) levels and intercellular quorum sensing autoinducer-2 (AI-2) contents were regularly measured. Resuscitation assays were conducted after obtaining VBNC cells. Gene expression was measured using real-time quantitative polymerase chain reaction (qPCR). The results showed that RpoS and low temperature conditions were associated with enhanced culturability and recoverability of Salmonella Enteritidis after desiccation storage in low water activity (aw) PIF. In addition, the synthesis of intracellular ROS and intercellular quorum sensing AI-2 was regulated by RpoS, inducing the formation and resuscitation of VBNC cells. Gene expression of soxS, katG and relA was found strongly associated with RpoS. Due to the lack of RpoS factor, the ΔrpoS strain could not normally synthesize SoxS, catalase and (p)ppGpp, resulting in its early shift to the VBNC state. This study elucidates the role of rpoS in desiccation stress and the formation and resuscitation mechanism of VBNC cells under desiccation stress. It serves as the basis for preventing and controlling the recovery of pathogenic bacteria in VBNC state in low aw foods.

Trans-epithelial migration is essential for neutrophil activation during RSV infection

The recruitment of neutrophils to the infected airway occurs early following respiratory syncytial virus (RSV) infection, and high numbers of activated neutrophils in the airway and blood are associated with the development of severe disease. The aim of this study was to investigate whether trans-epithelial migration is sufficient and necessary for neutrophil activation during RSV infection. Here, we used flow cytometry and novel live-cell fluorescent microscopy to track neutrophil movement during trans-epithelial migration and measure the expression of key activation markers in a human model of RSV infection. We found that when migration occurred, neutrophil expression of CD11b, CD62L, CD64, NE, and MPO increased. However, the same increase did not occur on basolateral neutrophils when neutrophils were prevented from migrating, suggesting that activated neutrophils reverse migrate from the airway to the bloodstream side, as has been suggested by clinical observations. We then combined our findings with the temporal and spatial profiling and suggest 3 initial phases of neutrophil recruitment and behavior in the airways during RSV infection; (1) initial chemotaxis; (2) neutrophil activation and reverse migration; and (3) amplified chemotaxis and clustering, all of which occur within 20 min. This work and the novel outputs could be used to develop therapeutics and provide new insight into how neutrophil activation and a dysregulated neutrophil response to RSV mediates disease severity.

Spatiotemporal dynamics of calcium signals during neutrophil cluster formation

Neutrophils form cellular clusters or swarms in response to injury or pathogen intrusion. Yet, intracellular signaling events favoring this coordinated response remain to be fully characterized. Here, we show that calcium signals play a critical role during mouse neutrophil clustering around particles of zymosan, a structural fungal component. Pioneer neutrophils recognizing zymosan or live Candida albicans displayed elevated calcium levels. Subsequently, a transient wave of calcium signals in neighboring cells was observed followed by the attraction of neutrophils that exhibited more persistent calcium signals as they reached zymosan particles. Calcium signals promoted LTB4 production while the blocking of extracellular calcium entry or LTB4 signaling abrogated cluster formation. Finally, using optogenetics to manipulate calcium influx in primary neutrophils, we show that calcium signals could initiate recruitment of neighboring neutrophils in an LTB4-dependent manner. Thus, sustained calcium responses at the center of the cluster are necessary and sufficient for the generation of chemoattractive gradients that attract neutrophils in a self-reinforcing process.

Inflammatory Microenvironment of Skin Wounds

Wound healing is a dynamic and highly regulated process that can be separated into three overlapping and interdependent phases: inflammation, proliferation, and remodelling. This review focuses on the inflammation stage, as it is the key stage of wound healing and plays a vital role in the local immune response and determines the progression of wound healing. Inflammatory cells, the main effector cells of the inflammatory response, have been widely studied, but little attention has been paid to the immunomodulatory effects of wound healing in non-inflammatory cells and the extracellular matrix. In this review, we attempt to deepen our understanding of the wound-healing microenvironment in the inflammatory stage by focusing on the interactions between cells and the extracellular matrix, as well as their role in regulating the immune response during the inflammatory stage. We hope our findings will provide new ideas for promoting tissue regeneration through immune regulation.

Neutrophils vs. amoebas: Immunity against the protozoan parasite Entamoeba histolytica

Entamoeba histolytica is a protozoan parasite with high prevalence in developing countries, and causes amoebiasis. This disease affects the intestine and the liver, and is the third leading cause of human deaths among parasite infections. E. histolytica infection of the intestine or liver is associated with a strong inflammation characterized by a large number of infiltrating neutrophils. Consequently, several reports suggest that neutrophils play a protective role in amoebiasis. However, other reports indicate that amoebas making direct contact with neutrophils provoke lysis of these leukocytes, resulting in the release of their lytic enzymes, which in turn provoke tissue damage. Therefore, the role of neutrophils in this parasitic infection remains controversial. Neutrophils migrate from the circulation to sites of infection, where they display several antimicrobial functions, including phagocytosis, degranulation, and formation of neutrophil extracellular traps (NET). Recently, it was found that E. histolytica trophozoites are capable of inducing NET formation. Neutrophils in touch with amoebas launched NET in an explosive manner around the amoebas and completely covered them in nebulous DNA and cell aggregates where parasites got immobilized and killed. In addition, the phenotype of neutrophils can be modified by the microbiome resulting in protection against amoebas. This review describes the mechanisms of E. histolytica infection and discusses the novel view of how neutrophils are involved in innate immunity defense against amoebiasis. Also, the mechanisms on how the microbiome modulates neutrophil function are described.

Coordinating a neutrophil swarm

Ca 2+ and ATP signaling control the self-organized, collective behaviors of neutrophils at wound sites.