The function of a neutrophil is to destroy and remove foreign substances. The neutrophil surrounds the foreign body and digests it with enzymes. Neutrophils make up about 60 percent of all white blood cells, or leukocytes.
Neutrophils congregate at the site of an injury or infection. They surround bacteria and consume them using lysosomes, which are structures within the cell that contain digestive enzymes. Neutrophils, along with eosinophils and basophils, are known as granulocytes because these cells contain a substance that looks like granules. These granules are actually the lysosomes.
Newly made neutrophils have a single, round nucleus. As they age, neutrophil nuclei break apart. A doctor can tell if the body is responding to an infection by observing whether or not the nuclei of the neutrophils are intact.
Neutrophils generally travel around the body in the bloodstream. About 3,000 to 6,000 neutrophils are normally present in each milliliter of blood. When an injury or infection occurs, blood starts accumulating around the site of the wound. Chemotactic factors are substances located on injured tissue and on foreign invaders such as bacteria. These factors attract neutrophils to the site of an injury or infection. Neutrophils stick to the inner cell layer of blood vessels at the site of injury. These leukocytes then squeeze through the cell layers of the blood vessels into the area between cells, known as the interstitial space, where they encounter the foreign substances and destroy them.