Neutrophil activation, acute lung injury and disease severity in Plasmodium knowlesi malaria

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Abstract
The risk of severe malaria from the zoonotic parasite Plasmodium knowlesi approximates that from P. falciparum. In severe falciparum malaria, neutrophil activation contributes to inflammatory pathogenesis, including acute lung injury (ALI). The role of neutrophil activation in the pathogenesis of severe knowlesi malaria has not been examined. We evaluated 213 patients with P. knowlesi mono-infection (138 non-severe, 75 severe) and 49 Plasmodium-negative controls from Malaysia. Markers of neutrophil activation (soluble neutrophil elastase [NE], citrullinated histone [CitH3] and circulating neutrophil extracellular traps [NETs]) were quantified in peripheral blood by microscopy and immunoassays. Findings were correlated with malaria severity, ALI clinical criteria, biomarkers of parasite biomass, haemolysis, and endothelial activation. Neutrophil activation increased with disease severity, with median levels higher in severe than non-severe malaria and controls for NE (380[IQR:210–930]ng/mL, 236[139–448]ng/mL, 218[134–307]ng/mL, respectively) and CitH3 (8.72[IQR:3.0–23.1]ng/mL, 4.29[1.46–9.49]ng/mL, 1.53[0.6–2.59]ng/mL, respectively)[all p<0.01]. NETs were higher in severe malaria compared to controls (126/μL[IQR:49–323] vs 51[20–75]/μL, p<0.001). In non-severe malaria, neutrophil activation fell significantly upon discharge from hospital (p0.24, p<0.05). Plasma NE and angiopoietin-2 were higher in knowlesi patients with ALI than those without (p<0.008); neutrophilia was associated with an increased risk of ALI (aOR 3.27, p<0.01). In conclusion, neutrophil activation is increased in ALI and in proportion to disease severity in knowlesi malaria, is associated with endothelial activation, and may contribute to disease pathogenesis. Trials of adjunctive therapies to regulate neutrophil activation are warranted in severe knowlesi malaria.
Funding Information
  • Australian Centre for International Agricultural Research (LS-2019-116)
  • National Health and Medical Research Council (1037304)
  • National Health and Medical Research Council (1045156)
  • National Health and Medical Research Council (1042072)
  • National Health and Medical Research Council (2017436)
  • National Health and Medical Research Council (2016792)
  • National Health and Medical Research Council (2025376)
  • NIH (R01AI160457-01)
  • Kementerian Kesihatan Malaysia (BP00500/117/1002)
  • Malaysia Australia Colombo Plan Commemoration (MACC) and Australian Government Research Training Program (RTP) Scholarship at Charles Darwin University
  • Australian Centre for International Agricultural Research, and Indo-Pacific Centre for Health Security, DFAT, Australian Government (LS-2019-116)

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