Eimeria ninakohlyakimovae casts NOX-independent NETosis and induces enhanced IL-12, TNF-α, IL-6, CCL2 and iNOS gene transcription in caprine PMN

NETosis in Parasitic Infections: A Puzzle That Remains Unsolved

Neutrophils are the key players in the innate immune system, being weaponized with numerous strategies to eliminate pathogens. The production of extracellular traps is one of the effector mechanisms operated by neutrophils in a process called NETosis. Neutrophil extracellular traps (NETs) are complex webs of extracellular DNA studded with histones and cytoplasmic granular proteins. Since their first description in 2004, NETs have been widely investigated in different infectious processes. Bacteria, viruses, and fungi have been shown to induce the generation of NETs. Knowledge is only beginning to emerge about the participation of DNA webs in the host's battle against parasitic infections. Referring to helminthic infections, we ought to look beyond the scope of confining the roles of NETs solely to parasitic ensnarement or immobilization. Hence, this review provides detailed insights into the less-explored activities of NETs against invading helminths. In addition, most of the studies that have addressed the implications of NETs in protozoan infections have chiefly focused on their protective side, either through trapping or killing. Challenging this belief, we propose several limitations regarding protozoan-NETs interaction. One of many is the duality in the functional responses of NETs, in which both the positive and pathological aspects seem to be closely intertwined.

Glycolysis, monocarboxylate transport, and purinergic signaling are key events in Eimeria bovis-induced NETosis

The protozoan parasite Eimeria bovis is the causative agent of bovine coccidiosis, an enteric disease of global importance that significantly affects cattle productivity. Previous studies showed that bovine NETosis—an important early host innate effector mechanism of polymorphonuclear neutrophil (PMN)—is elicited by E. bovis stages. So far, the metabolic requirements of E. bovis-triggered NET formation are unknown. We here studied early glycolytic and mitochondrial responses of PMN as well as the role of pH, distinct metabolic pathways, P2 receptor-mediated purinergic signaling, and monocarboxylate transporters 1 and 2 (MCT1, MCT2) in E. bovis sporozoite-induced NET formation. Seahorse-based experiments revealed a rapid induction of both neutrophil oxygen consumption rate (OCR) and early glycolytic responses, thereby reflecting immediate PMN activation and metabolic changes upon confrontation with sporozoites. The impact of these metabolic changes on NET formation was studied via chemical inhibition experiments targeting glycolysis and energy generation by the use of 2-fluor-2-deoxy-D-glucose (FDG), 6-diazo-5-oxo-L-norleucin (DON), sodium dichloroacetate (DCA), oxythiamine (OT), sodium oxamate (OXA), and oligomycin A (OmA) to block glycolysis, glutaminolysis, pyruvate dehydrogenase kinase, pyruvate dehydrogenase, lactate dehydrogenase, and mitochondrial ATP-synthase, respectively. Overall, sporozoite-induced NET formation was significantly diminished via PMN pretreatments with OmA and OXA, thereby indicating a key role of ATP- and lactate-mediated metabolic pathways. Consequently, we additionally studied the effects of extracellular pH, MCT1, MCT2, and purinergic receptor inhibitors (AR-C141900, AR-C155858, theobromine, and NF449, respectively). Pretreatment with the latter inhibitors led to blockage of sporozoite-triggered DNA release from exposed bovine PMN. This report provides first evidence on the pivotal role of carbohydrate-related metabolic pathways and purinergic receptors being involved in E. bovis sporozoite-induced NETosis.

A Review of the Neutrophil Extracellular Traps (NETs) from Cow, Sheep and Goat Models

This review provides insight into the importance of understanding NETosis in cows, sheep, and goats in light of the importance to their health, welfare and use as animal models. Neutrophils are essential to innate immunity, pathogen infection, and inflammatory diseases. The relevance of NETosis as a conserved innate immune response mechanism and the translational implications for public health are presented. Increased understanding of NETosis in ruminants will contribute to the prediction of pathologies and design of strategic interventions targeting NETs. This will help to control pathogens such as coronaviruses and inflammatory diseases such as mastitis that impact all mammals, including humans. Definition of unique attributes of NETosis in ruminants, in comparison to what has been observed in humans, has significant translational implications for one health and global food security, and thus warrants further study.