Mouse Neutrophil Extracellular Traps in Microbial Infections (1)
Other immune cells, such as mast cells and eosinophils, were found to release NET-like structures that were collectively termed extracellular traps (ETs ).
Gp91 is a subunit of the NADPH oxidase. In its absence, the enzyme complex is not functional, and mice deficient in gp91 (gp91–/–) are unable to produce ROS. Upon PMA stimulation, wild type neutrophils underwent cell death, whereas gp91–/– neutrophils did not, but rather survived longer than the unstimulated control. 40% of all wild-type neutrophils died upon activation with PMA. In contrast, neutrophils isolated from gp91–/– mice survived longer than 16 h and activation with PMA increased their survival. 8 h after PMA stimulation, wild-type neutrophils showed a complete loss of cytoplasmic and nuclear organization, evidenced by the disintegration of the nuclear envelope.
After 4 h, the nuclei of more than 75% of the wild-type neutrophils were delobulated. In this intermediate stage, the nuclei stained homogeneously for histone/DNA complexes. After 16 h of stimulation, 59.8% of the cells remained in this state without releasing NETs. However, the amount of NETs increased continuously to a maximum of 30% after 16 h
SJL and CD1 mice produced more ROS (between 130 and 150%) compared to neutrophils from C57Bl/6. ROS production in neutrophils from BALB/c, 129 and PLJ was similar to the standard. On average, 20% more neutrophils from SJL mice and 30% fewer neutrophils from Czech mice died compared to C57Bl/6. Neutrophils from CD1, BALB/c, PLJ and 129 mice differed by only 12%. The efficiency of ROS production significantly correlates to NET cell death.
The response to hyphae was nearly 20 times stronger than that to yeast. Under both conditions, ROS production reached a maximum at around 90 min after infection.
In human neutrophils, it takes 3–4 h until about 80% of the cells have undergone NETosis. In contrast, murine neutrophils require about 16 h until approximately 30% of the stimulated mouse neutrophils have released NETs. This indicates that NET formation by mouse neutrophils takes longer and is less efficient than by human neutrophils. However, the role of NETs in bacterial infections of the mouse is clearly established.