The human immune system is a complex set of cells and organs that protects the body from invaders. These invaders include bacteria, parasites and viruses. Sometimes invaders are able to get past this first line of defense. Once microbes enter the body, other immune system components come into play. These cells include neutrophils and macrophages.
Neutrophils are members of a class of white blood cells known as granulocytes .
Other types of granulocytes are eosinophils and basophils , which are involved in allergic reactions. Granulocytes contain reservoirs that store toxic chemicals. Neutrophils reside in the bone marrow until they are needed, and are then carried in the bloodstream to sites of injury or infection. These cells are the body's main defense against bacteria. When a neutrophil ingests a microbe, the cell's toxic chemicals kill and digest it.