Neutrophils

The neutrophils are the most plentiful of all white blood cells. They live fairly short lives, lasting for around 5.4 days, and during this time they "roam" the body, searching out pathogens. As I mentioned above, they tend to be the first respondents and will flood a site of infection, navigating by means of chemotaxis.

Once there, being phagocytes, one of the things they do is phagocytise any pathogens that they come across. They are also capable of releasing inflammatory cytokines and recruiting other immunocompetent cells. As I have stated before, neutrophils are granulocytes, as well as phagocytes, and - like mast cells - can be stimulated to release their granules, which are very effective at killing pathogens.

The other extremely interesting thing that they do is form neutrophil extracellular traps (NETs). These are actually reminiscent of nets - they're fibres of DNA. The fibres are composed of chromatin as well as serine and other proteins from neutrophil granules. These proteins then destroy invading pathogens. Brilliantly, it seems that the NETs may actually serve as nets - trapping pathogens. They also prevent the antimicrobial proteins from doing serious damage to the body, as they are kept attached to the neutrophil.

Neutrophils look like this:

(a) Some actual neutrophils (giemsa stained). (Image courtesy Dr Graham Beards (via Wikipedia))

(b) A schematic representation of a neutrophil. (Image courtesy "A. Rad" (via Wikipedia))

Figure 1.53: The neutrophil