Bacteria induce prolonged PMN survival via a phosphatidylcholine-specific phospholipase C- and protein kinase C-dependent mechanism

Pre-metastatic Niche Formation by Neutrophils in Different Organs

Metastasis is a multistep process requiring tumor cell detachment from the primary tumor and migration to secondary target organs through the lymphatic or blood circulatory systems. In certain cancers, specific organs are predisposed to metastases. Metastatic homing to distant organs is orchestrated by the formation of supportive metastatic microenvironment in such organs, called pre-metastatic niche. Formation of pre-metastatic niche depends on the primary tumor-mediated recruitment of bone marrow-derived myeloid cells, including neutrophils. The contribution of neutrophils to the formation of the pre-metastatic niche is recently getting growing attention. Of note, these cells can either stimulate or inhibit metastatic seeding, depending on the activation of these cells. Here, we concentrate on pro-metastatic functions of neutrophils and the mechanisms involved in this process. Pro-tumor neutrophils support the formation of pre-metastatic niche, attract tumor cells, and directly stimulate proliferation of these cells. Moreover, immunosuppressive neutrophils, also called granulocytic MDSC, promote metastatic progression by the inhibition of antitumor T-cells. Altogether, neutrophil pro-tumor properties significantly affect metastatic spread in the host. Here, we provide an up-to-date overview of roles neutrophils play in the regulation of metastatic processes in different organs.

Yersinia pseudotuberculosis Blocks Neutrophil Degranulation

Neutrophils are essential components of immunity and are rapidly recruited to infected or injured tissue. Upon their activation, neutrophils release granules to the cell's exterior, through a process called degranulation. These granules contain proteins with antimicrobial properties that help combat infection. The enteropathogenic bacterium Yersinia pseudotuberculosis successfully persists as an extracellular bacterium during infection by virtue of its translocation of virulence effectors (Yersinia outer proteins [Yops]) that act in the cytosol of host immune cells to subvert phagocytosis and proinflammatory responses. Here, we investigated the effect of Y. pseudotuberculosis on neutrophil degranulation upon cell contact. We found that virulent Y. pseudotuberculosis was able to prevent secondary granule release. The blocking effect was general, as the release of primary and tertiary granules was also reduced. Degranulation of secondary granules was also blocked in primed neutrophils, suggesting that this mechanism could be an important element of immune evasion. Further, wild-type bacteria conferred a transient block on neutrophils that prevented their degranulation upon contact with plasmid-cured, avirulent Y. pseudotuberculosis and Escherichia coli Detailed analyses showed that the block was strictly dependent on the cooperative actions of the two antiphagocytic effectors, YopE and YopH, suggesting that the neutrophil target structures constituting signaling molecules needed to initiate both phagocytosis and general degranulation. Thus, via these virulence effectors, Yersinia can impair several mechanisms of the neutrophil's antimicrobial arsenal, which underscores the power of its virulence effector machinery.

Spatially distinct neutrophil responses within the inflammatory lesions of pneumonic plague

During pneumonic plague, the bacterium Yersinia pestis elicits the development of inflammatory lung lesions that continue to expand throughout infection. This lesion development and persistence are poorly understood. Here, we examine spatially distinct regions of lung lesions using laser capture microdissection and transcriptome sequencing (RNA-seq) analysis to identify transcriptional differences between lesion microenvironments. We show that cellular pathways involved in leukocyte migration and apoptosis are downregulated in the center of lung lesions compared to the periphery. Probing for the bacterial factor(s) important for the alteration in neutrophil survival, we show both in vitro and in vivo that Y. pestis increases neutrophil survival in a manner that is dependent on the type III secretion system effector YopM. This research explores the complexity of spatially distinct host-microbe interactions and emphasizes the importance of cell relevance in assays in order to fully understand Y. pestis virulence.

Yersinia pestis is a high-priority pathogen and continues to cause outbreaks worldwide. The ability of Y. pestis to be transmitted via respiratory droplets and its history of weaponization has led to its classification as a select agent most likely to be used as a biological weapon. Unrestricted bacterial growth during the initial preinflammatory phase primes patients to be infectious once disease symptoms begin in the proinflammatory phase, and the rapid disease progression can lead to death before Y. pestis infection can be diagnosed and treated. Using in vivo analyses and focusing on relevant cell types during pneumonic plague infection, we can identify host pathways that may be manipulated to extend the treatment window for pneumonic plague patients.