Neutrophils (known in some literature as neutrophiles) are granular
white blood cells. They are the most common type of WBC and compose 55%-70% of the WBC population in a person's
immune system.
Neutrophils are sort of the cellular equivalent of the Marines. The cells play a leading role in the body's inflammation response and they are responsible for most of the body's infection protection. These cells home in on foreign matter in the body and destroy invaders and antigens by phagocytosis. If a neutrophil is killed during inflammation, the dying cell releases a chemical that dissolves all the other cells in the immediate area. This soupy, sticky blend of neutrophil-nuked cells is what we see as pus.
Unfortunately, neutrophils can, in the inflammatory heat of a fierce cellular battle, start attacking the body's own normal cells. And sometimes a misguided neutrophil attack happens spontaneously in an autoimmune disorder. Tissue damage can be extensive. This is what happens in diseases such as rheumatoid arthritis and inflammatory bowel disease.