Microbes and the fate of neutrophils

Neutrophils or polymorphonuclear neutrophils (PMNs) are an important component of innate host defense. These phagocytic leukocytes are recruited to infected tissues and kill invading microbes. There are several general characteristics of neutrophils that make them highly effective as antimicrobial cells. First, there is tremendous daily production and turnover of granulocytes in healthy adults-typically 1011 per day. The vast majority (~95%) of these cells are neutrophils. In addition, neutrophils are mobilized rapidly in response to chemotactic factors and are among the first leukocytes recruited to infected tissues. Most notably, neutrophils contain and/or produce an abundance of antimicrobial molecules. Many of these antimicrobial molecules are toxic to host cells and can destroy host tissues. Thus, neutrophil activation and turnover are highly regulated processes. To that end, aged neutrophils undergo apoptosis constitutively, a process that contains antimicrobial function and proinflammatory capacity. Importantly, apoptosis facilitates nonphlogistic turnover of neutrophils and removal by macrophages. This homeostatic process is altered by interaction with microbes and their products, as well as host proinflammatory molecules. Microbial pathogens can delay neutrophil apoptosis, accelerate apoptosis following phagocytosis, or cause neutrophil cytolysis. Here, we review these processes and provide perspective on recent studies that have potential to impact this paradigm.

Dysregulation of neutrophil death in sepsis

Sepsis is a prevalent disease that has alarmingly high mortality rates and, for several survivors, long-term morbidity. The modern definition of sepsis is an aberrant host response to infection followed by a life-threatening organ dysfunction. Sepsis has a complicated pathophysiology and involves multiple immune and non-immune mediators. It is now believed that in the initial stages of sepsis, excessive immune system activation and cascading inflammation are usually accompanied by immunosuppression. During the pathophysiology of severe sepsis, neutrophils are crucial. Recent researches have demonstrated a clear link between the process of neutrophil cell death and the emergence of organ dysfunction in sepsis. During sepsis, spontaneous apoptosis of neutrophils is inhibited and neutrophils may undergo some other types of cell death. In this review, we describe various types of neutrophil cell death, including necrosis, apoptosis, necroptosis, pyroptosis, NETosis, and autophagy, to reveal their known effects in the development and progression of sepsis. However, the exact role and mechanisms of neutrophil cell death in sepsis have not been fully elucidated, and this remains a major challenge for future neutrophil research. We hope that this review will provide hints for researches regarding neutrophil cell death in sepsis and provide insights for clinical practitioners.

Mcl-1 Inhibition: Managing Malignancy in Multiple Myeloma

Multiple myeloma (MM) is a plasma cells neoplasm. The overexpression of Bcl-2 family proteins, particularly myeloid cell leukemia 1 (Mcl-1), plays a critical role in the pathogenesis of MM. The overexpression of Mcl-1 is associated with drug resistance and overall poor prognosis of MM. Thus, inhibition of the Mcl-1 protein considered as a therapeutic strategy to kill the myeloma cells. Over the last decade, the development of selective Mcl-1 inhibitors has seen remarkable advancement. This review presents the critical role of Mcl-1 in the progression of MM, the most prominent BH3 mimetic and semi-BH3 mimetic that selectively inhibit Mcl-1, and could be used as single agent or combined with existing therapies.

Mouse Models and Tools for the in vivo Study of Neutrophils

Neutrophils are the most abundant leukocytes in human blood and critical actors of the immune system. Many neutrophil functions and facets of their activity in vivo were revealed by studying genetically modified mice or by tracking fluorescent neutrophils in animals using imaging approaches. Assessing the roles of neutrophils can be challenging, especially when exact molecular pathways are questioned or disease states are interrogated that alter normal neutrophil homeostasis. This review discusses the main in vivo models for the study of neutrophils, their advantages and limitations. The side-by-side comparison underlines the necessity to carefully choose the right model(s) to answer a given scientific question, and exhibit caveats that need to be taken into account when designing experimental procedures. Collectively, this review suggests that at least two models should be employed to legitimately conclude on neutrophil functions.

Inhibition of apoptosis induced by heat shock preconditioning is associated with decreased phagocytosis in human polymorphonuclear leukocytes through inhibition of Rac and Cdc42

The functionality of polymorphonuclear leukocytes (PMNL) and the exact process of the protective program employed by these cells in response to the heat shock (HS) remain ill-defined and debated. Particularly, the mechanism of phagocytic impairment induced by the HS and the molecular events associated with the delay of apoptosis used by these cells in such condition have given conflictual data. The aim of the present work is to study the consequences of the HS in different pathways involved in human PMNL apoptosis and subsequently in human PMNL phagocytic function. We demonstrated that HS (41 degrees C, 1 h) preconditioning induced inhibition of spontaneous PMNL apoptosis observed at 18 h in control cells incubated at 37 degrees C. This inhibition was characterized by absence of morphological nuclear changes, decrease of DNA fragmentation, low level of annexin V expression and decrease of caspase-3 activity. In parallel, HS increased both Hsp70 and Mcl-1 protein levels in PMNL. Phagocytosis of latex beads by PMNL was inhibited by HS (41 degrees C, 1 h) preconditioning despite an upregulation of CD11b, CD16 and CD47. Moreover, HS induced prolonged F actin depolymerization and inhibited both Rac and Cdc42 activation in PMNL. Finally, our results identify a new function of Mcl-1 in HS protection against apoptosis.