Table 1.

Limitations in studying NETs in asthma.

•Most if not all studies on the role of NETs in asthma have been performed on bulk analysis of neutrophils. Human neutrophils are highly heterogeneous [45,46,47,48], and different subsets of neutrophils could produce different forms of NETs.

•We do not know the role of neutrophil subsets and their specific mediators, including NETs, in different phenotypes of asthma.

•We do not know whether subsets of neutrophils make different NETs.

•We do not know whether NETs in different phases (early vs. late) or phenotypes of asthma (T2-high vs. T2-low) are proinflammatory or anti-inflammatory.

•In human studies, most experimental approaches are limited to ex vivo analyses of NET formation by blood neutrophils and basic correlations with clinical outcomes. However, these approaches do not provide insights into the underlying causes of disease.

•Approximately 25% of neutrophils release vital NETs [74]. We do not know the role of non-lytic and lytic NETs in asthma.

•Primary human neutrophils cannot undergo transfection and it is difficult to specifically inhibit pathways that lead to NET formation in vivo.

•Several immune cells, such as eosinophils, mast cells, macrophages, and basophils can release extracellular DNA traps.

•In vivo identification of NETs requires the colocalization of at least three molecules: extracellular DNA, histones, and neutrophil elastase.

•We do not know whether allergen immunotherapy modulates NET formation in vivo.