“NETs and EETs, a Whole Web of Mess”

Abstract

Neutrophils and eosinophils are granulocytes that have very distinct functions. Neutrophils are first responders to external threats, and they use different mechanisms to control pathogens. Phagocytosis, reactive oxygen species, and neutrophil extracellular traps (NETs) are some of the mechanisms that neutrophils utilize to fight pathogens. Although there is some controversy as to whether NETs are in fact beneficial or detrimental to the host, it mainly depends on the biological context. NETs can contribute to disease pathogenesis in certain types of diseases, while they are also undeniably critical components of the innate immune response. On the contrary, the role of eosinophils during host immune responses remains to be better elucidated. Eosinophils play an important role during helminthic infections and allergic responses. Eosinophils can function as effector cells in viral respiratory infections, gut bacterial infections, and as modulators of immune responses by driving the balance between Th1 and Th2 responses. In particular, eosinophils have biological activities that appear to be quite similar to those of neutrophils. Both possess bactericidal activity, can activate proinflammatory responses, can modulate adaptive immune responses, can form extracellular traps, and can be beneficial or detrimental to the host according to the underlying pathology. In this review we compare these two cell types with a focus on highlighting their numerous similarities related to extracellular traps.

Significance of NETs Formation in COVID-19

“…The increased neutrophil to lymphocyte ratio (NLR) as well as the reduced number of T CD8+ are described as an independent prognostication factor within the early phase of SARS-CoV-2 infection, signaling a severe progression of COVID-19 [5,11,12]. This is confirmed by research completed by Leppkes et al (2020), where a significant rise in the overall number of leukocytes and neutrophilia and an elevated NLR in the severe progression of the disease, in comparison to its mild form as well as in patients who have recovered from the illness, were seen [13,14].…”

Acute Eosinophilic Pneumonia Complicated with Venous Thromboembolic Disease—Diagnostic and Therapeutic Considerations

“…The most interesting problem concerning the presented patient was the possible impact of AEP on the coagulation system, resulting in acute VTE development. The data included in the literature confirm that both systemic and pulmonary eosinophilia results in enhanced coagulation mechanisms [ 6 , 13 , 14 ]. Activated eosinophils eject mitochondrial DNA and release granules’ contents, among others—eosinophil peroxidase (EP) and eosinophil cationic protein (ECP), with subsequent forming the eosinophil extracellular traps (EETs) [ 13 ].…”

Eosinophils and Bacteria, the Beginning of a Story

“…Eosinophils are granulocytes with a segmented nucleus. Their dense granules contain cationic proteins, which include the major basic protein (MBP), eosinophil peroxidase (EPX), eosinophil cationic protein (ECP), and the eosinophil derived neurotoxin (EDN) [ 6 , 7 , 8 ]. The versatility of these granulocytes in homeostasis and immunity is gradually becoming better understood [ 9 ].…”

“…A complementary mechanism by which eosinophils exert direct pathogen immunity is through the formation of extracellular DNA traps, which consist of extruded DNA enmeshed with histones and cationic proteins [ 7 , 64 , 65 , 66 ]. Traps have been reported during gastrointestinal bacterial infections [ 22 ], where they have been associated with localized infection containment [ 67 ].…”

“…Charcot–Leyden crystal protein (CLC-P), also known as galectin-10, has been closely associated with eosinophils traps and may also be linked to their formation [ 68 , 69 ]. Extracellular traps have been correlated with several autoinflammatory and infectious diseases [ 7 ], although their role during immune response and pathogenesis is not fully clear. In addition to their phagocytic capabilities and extracellular trap formation, there is increasing evidence that associates eosinophils with immune responses to bacterial infections.…”