Neutrophils are one of the three types of granulocytes of the immune system; the others being eosinophils and basophils. These are white blood cells (leukocytes) which contains glycogen granules in their cytoplasm. Neutrophils are polymorphonuclear cells, which means their nucleus is highly variable, having three, four and sometimes five lobes. They are the most common white blood cells in the normal human peripheral blood, constituting between 40% and 65% of all leukocytes in the bloodstream.
Function
The main function of neutrophils is the phagocytosis and destruction of bacteria. It means the engulfing and ingestion of this type of microbe. Bacteria are phagocytosed after opsonization (the process by which a bacterium is weakened before being destroyed).
Structure
A neutrophil is between 12 and 15 μm in diameter. The nucleus has three to five lobes, contains no nucleolus, and it is largely heterochromatin. The cytoplasm has only a few mitochondria, a Golgi apparatus, and little endoplasmatic reticulum; it also contains many glycogen granules. (glycogen is a form of sugar = carbohydrate). The neutrophils have two varieties of membrane-bound granules, which are modified lysosomes and have a bacteriological function. They also have cortical microfilaments and some cytoplasmic microtubules.
How a bacterium is destroyed by a neutrophil
The membrane-bound azurophilic granules (primary or type A) contains myeloperoxidase, which is an enzyme that produces bacterocidal molecular oxygen from hydrogen peroxide (H2 O2). This corrodes the bacterium membrane. Meanwhile, specific granules have a special protein called lactoferrin, which binds to the ferric ions of bacteria that is required for bacterial multiplication.
A light micrograph of two neutrophils among erythrocytes in a normal human peripheral blood smear.
