1.
Differential antibacterial control by neutrophil subsets.
Leliefeld, PHC, Pillay, J, Vrisekoop, N, Heeres, M, Tak, T, Kox, M, Rooijakkers, SHM, Kuijpers, TW, Pickkers, P, Leenen, LPH, et al
Blood advances. 2018;(11):1344-1355
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Abstract
Neutrophils comprise a heterogeneous population of cells essential for bacterial eradication, and defects in neutrophil function are associated with increased susceptibility to infection. In this study, neutrophils from healthy controls were shown to prevent bacterial proliferation for at least 48 hours when cocultured with methicillin-resistant Staphylococcus aureus (MRSA) in tissue-like scaffolds by establishing a bacteriostatic environment inside their phagolysosome. This intracellular bacterial containment is independent of reactive oxygen species because neutrophils that lack a functional nicotinamide adenine dinucleotide phosphate-oxidase complex displayed no defect in intracellular bacterial containment, whereas killing of the pathogen was impaired. During acute inflammation, a subset of CD16bright/CD62Ldim hypersegmented neutrophils displayed normal phagocytosis associated with a remarkably poor capacity to contain bacteria intracellularly. Conversely, CD16dim-banded neutrophils were the only neutrophil subset that adequately contained MRSA. These findings demonstrate a clear neutrophil heterogeneity in their antimicrobial capacity and the appearance of neutrophil subsets with a clear differentiation in functionality during acute inflammation. Furthermore, this study provides an evolutionary basis for the rapid release of banded neutrophils into the circulation during acute inflammation.
2.
SK3 channel and mitochondrial ROS mediate NADPH oxidase-independent NETosis induced by calcium influx.
Douda, DN, Khan, MA, Grasemann, H, Palaniyar, N
Proceedings of the National Academy of Sciences of the United States of America. 2015;(9):2817-22
Abstract
Neutrophils cast neutrophil extracellular traps (NETs) to defend the host against invading pathogens. Although effective against microbial pathogens, a growing body of literature now suggests that NETs have negative impacts on many inflammatory and autoimmune diseases. Identifying mechanisms that regulate the process termed "NETosis" is important for treating these diseases. Although two major types of NETosis have been described to date, mechanisms regulating these forms of cell death are not clearly established. NADPH oxidase 2 (NOX2) generates large amounts of reactive oxygen species (ROS), which is essential for NOX-dependent NETosis. However, major regulators of NOX-independent NETosis are largely unknown. Here we show that calcium activated NOX-independent NETosis is fast and mediated by a calcium-activated small conductance potassium (SK) channel member SK3 and mitochondrial ROS. Although mitochondrial ROS is needed for NOX-independent NETosis, it is not important for NOX-dependent NETosis. We further demonstrate that the activation of the calcium-activated potassium channel is sufficient to induce NOX-independent NETosis. Unlike NOX-dependent NETosis, NOX-independent NETosis is accompanied by a substantially lower level of activation of ERK and moderate level of activation of Akt, whereas the activation of p38 is similar in both pathways. ERK activation is essential for the NOX-dependent pathway, whereas its activation is not essential for the NOX-independent pathway. Despite the differential activation, both NOX-dependent and -independent NETosis require Akt activity. Collectively, this study highlights key differences in these two major NETosis pathways and provides an insight into previously unknown mechanisms for NOX-independent NETosis.