Eosinophils are a type of white blood cell produced by the body to fight infection. They are an important part of the body's immune system, as they play a major role in fighting viruses and bacteria, as well as helping the body to identify and get rid of abnormal cells and substances. When someone has an allergic reaction, the body releases a large amount of eosinophils to the area, in order to fight off the allergen.

Eosinophils are produced in the bone marrow, and are one of the five types of white blood cells in the immune system. They are also found in the blood and in other tissue such as the lungs and spleen. Eosinophils have several roles, including fighting against parasites, allergens, and other pathogens, as well as helping to identify and eliminate abnormal cells, such as cancer cells.

Eosinophils are made up of several components. They contain enzymes, called granules, which can neutralize bacteria, viruses, and other foreign substances. They also contain various proteins, including cytokines and interleukins, which can activate other parts of the immune system, such as the production of antibodies.

Eosinophil count can be measured in order to ascertain the person’s health status. A low eosinophil count may indicate a weakened immune system, while a high eosinophil count may indicate a severe allergic reaction or a parasitic infection. High eosinophil counts can also accompany autoimmune diseases, such as asthma or hay fever.

Eosinophilic disorders are a group of disorders characterized by an abnormally high eosinophil count. The most common eosinophilic disorder is eosinophilic esophagitis, which is a chronic inflammatory condition of the esophagus, caused by an overproduction of eosinophils. Another eosinophilic disorder is hypereosinophilic syndrome, which is an extreme and prolonged elevation of eosinophils, which can lead to complications such as an enlarged heart.

In summary, eosinophils are an important part of the body's immune system, helping it to fight infection and foreign substances. The eosinophil count can be measured in order to assess a person’s health, and high eosinophil counts can indicate a variety of disorders, such as eosinophilic esophagitis and hypereosinophilic syndrome.