A type of white blood cell roaming around in blood in your body expels all it’s inner contents mainly DNA, in form of a ‘net’ to trap and kill bacteria and other microbes (imagine trapping bacteria in a sticky mesh and killing them). Sounds gore! No need to mention the poor cell dies (commits suicide to save the body) as it loses it’s DNA in the process.
Doesn’t it sound like a sci-fi movie?
When I first learnt about this process in Medical school, I was fascinated.
This process is called as Netosis and the cells which have this special superpower are Neutrophils. Neutrophils are a type of white blood cells. They are the most abundant of white blood cells, accounting for 60 to 70% of all white blood cells.
NET stands for Neutrophil Extracellular Traps. So the process was named as NETosis.
Neutrophil extracellular trap (NET) formation. Scanning electron microscopy of neutrophil (yellow) casting a net (green) entrapping Helicobacter pylori bacteria (blue).
Immunofluorescence confocal microscopy to visualize NETs. Neutrophils forming extracellular traps that are characterized by extracellular filaments of chromatin decorated with granular proteins. Cells were stained with anti-MPO (red) and counterstained with Hoechst 33342 (blue).
A scanning electron micrograph shows stimulated neutrophils forming NETs to trap Shigella flexneri (a type of bacteria).
Netosis was first discovered in 2004 (it’s a fairly new discovery). High-resolution scanning electron microscopy has shown that NETs consist of stretches of DNA and globular protein domains with diameters of 15-17 nm and 25 nm, respectively. These aggregate into larger threads with a diameter of 50 nm. NETs contain proteins from various granules of neutrophil cells.
A scanning electron micrograph. PMN (polymorphonuclear cell) is other name for neutrophil.
A scanning electron micrograph shows PMN/ Neutrophil trapping malarial parasite (Pb). Seems like it shot slime towards Pb and trapped it.
A scanning electron micrograph shows PMN/ Neutrophil trapping malarial parasite (Pb).
(All images from Google)
However, Neutrophil extracellular traps (NETs) can also play a role in causing various autoimmune conditions. They have been implicated in diseases like rheumatoid arthritis (RA), systemic lupus erythematosus, vasculitis and multiple sclerosis (MS). NETosis seems to be a major triggering event common to these rare disorders. NETosis can also induce damage to blood vessels and increases risk of clotting.
So what evolutionary may have evolved as a protective mechanism, in rare instances can be responsible for causing diseases as well.