Impaired neutrophil extracellular trap formation in β-thalassaemia/HbE

Neutrophil dysfunction contributes to a high susceptibility to severe bacterial infection which is a leading cause of morbidity and mortality in β-thalassaemia/HbE, especially in splenectomised patients. This study demonstrated another abnormality of neutrophil function, namely neutrophil extracellular trap (NET) formation in splenectomised and non-splenectomised β-thalassaemia/HbE patients who had iron overload. A classification system of morphological NET formation using confocal microscopy was developed, and samples were categorized into early and late phases which were subdivided into web-like and non-web structures. At baseline, neutrophils from non-splenectomised patients (58 ± 4%) and splenectomised patients (65 ± 3%) had higher early phase NETs than those from normal subjects (33 ± 1%). As a mimic of iron overload and infection, haemin/PMA/LPS treatment led to a significant reduction of early NETs and an increase of late NETs in neutrophils from normal and non-splenectomised patients. Interestingly, neutrophils from splenectomised patients had impaired development of late NETs. This suggests that during infection bacteria might not be trapped and may spread from the site of infection resulting in higher susceptibility to severe bacterial infection in splenectomised patients.