Eosinophils are a type of white blood cell which destroys parasitic larvae. They are granulocytes, which means they are leukocytes that have granule-like bodies in their cytosol. The other two types of granulocytes in the immune system are neutrophils and basophils. Eosinophils comprise only 1%, sometimes 2%, of all leukocytes in the blood. A cubic millimeter (1 m3) of blood contains about 200 of them.
Description
Eosinophils are motile phagocytic cells, which means they are moving white blood cells which have the capacity to engulf and destroy pathogenic microorganisms that have invaded the body. They are similar in size to the neutrophils, with a diameter of 12 or 15 μm (micron). However, they have a different aspect in the light microscope. The nucleus has two or three lobes, which contain an striking array of red or orange eosinophilic granules.
An eosinophil has a typical cell membrane and cytoplasm, in which scattered mitochondria can be found. It also has one Golgi apparatus near the nucleus, numerous eosinophilic granules, which are modified lysosomes. These eosinophilic granules have prominent crystaloids. Microfilaments can also be found near the cortex.
Functions
The eosinophils kill parasitic larvae as the enter the peripheral blood or the lamina propria of the gut. When parasites invade the body, mast cells* draw eosinophils to the infection site. Specifically, mast cells attract eosinophils by secreting eosinophil chemotactil factor. Lymphokines also draw this type of white blood cell to the site of inflammation. Thus, eosinophils help regulate mast cell response to inflammation by releasing an enzymes, which degrade the histamines secreted by mast cells at the site of infection.
*Mast cells are produced in the bone marrow and function in allergic reactions and immune response.
Below, diagrammatic picture of an eosinophil.
