NETosis and Neutrophil Activity Quantification in Pediatric Patients with Essential Thrombocythemia

Elevated levels of neutrophil extracellular traps (NETs) are associated with thrombotic risks, in particular, for patients with elevated platelet counts, such as those with essential thrombocythemia (ET). Here, the tendency for NETosis and neutrophil activity in such patients was assessed. A total of forty-one pediatric patients with elevated platelet counts diagnosed with ET (nine with CALR driver mutation, eleven with JAK2, thirteen triple-negative, and one dual-negative (TN)) or secondary thrombocytosis (five) were recruited. The tendency for NETosis was determined in a leucocyte-rich blood plasma smear using immunofluorescence staining with antibodies against myeloperoxidase and elastase. Activity of neutrophils was assessed ex vivo in parallel-plate flow chambers. The mean level of NETosis in healthy volunteers was 2.7-6.7% (95% CI). Among the ET patients, there was no statistically significant difference in NETosis level between those with mutations in CALR (19-43%), JAK2 (22-58%), and TN ones (6-27%). Patients with secondary thrombocytosis also had an elevated level of NETosis (8-66%). The velocity of neutrophil chemotaxis was significantly increased in all patients, in particular for those with mutations in CALR. These data reveal a major shift in the neutrophil activity in ET and suggest that the immunomorphological techniques presented here may allow reproducible and widely available characterization of neutrophil status.