Eosinophils are a specific type of white blood cell. These cells are a component of the immune system and play a part in the body’s defense mechanisms. Although they constitute a small percentage of total white blood cells, typically less than five percent in healthy individuals, their presence is important for maintaining overall health.
Visual Features of Eosinophils
When viewed under a microscope, eosinophils exhibit distinct characteristics. They are generally larger than red blood cells, measuring approximately 12 to 17 micrometers in diameter, which is about 1.5 to 3 times the size of a typical red blood cell. This size difference often makes them stand out in a blood smear.
A defining feature of an eosinophil is its bilobed nucleus. This bilobed nucleus can sometimes appear horseshoe-shaped or like two connected parts, resembling spectacles. While about 80% of mature eosinophils display this classic two-lobed structure, some may present with three lobes.
The cytoplasm of an eosinophil is filled with numerous large granules that appear a reddish-orange or bright pink color after staining. These granules readily absorb acidic dyes like eosin, which is how these cells received their name, meaning “eosin-loving.” The vivid staining of these granules is a primary identifier when observing them in blood or tissue samples.
Eosinophils’ Role in the Body
Eosinophils are primarily recognized for their involvement in combating specific types of infections. A significant role is their defense against parasites, such as parasitic worms (helminths). They release toxic proteins from their granules, which are capable of damaging or destroying these larger invaders.
Beyond parasitic defense, eosinophils are also participants in allergic reactions. They are implicated in conditions like asthma, hay fever, and eczema. During an allergic response, eosinophils can release inflammatory mediators, contributing to the symptoms and tissue changes observed in these conditions.
Eosinophils also have a recognized role in tissue repair. They contribute to the integrity of tissues and can be recruited to sites of injury. At these locations, they may release growth factors and other substances that support the healing process, including components involved in coagulation and fibrinolysis.
What High Eosinophil Levels Mean
An elevated count of eosinophils in the blood, a condition known as eosinophilia, often indicates an underlying health issue. The most common reasons for increased eosinophil levels are allergic conditions. These can include seasonal allergies, asthma, eczema, and reactions to certain medications.
Another frequent cause of eosinophilia is parasitic infections, particularly those caused by worms. While allergies and parasitic infections are the most common culprits, other causes exist. These can encompass certain autoimmune diseases, some types of cancer, or specific drug reactions.
When high eosinophil levels are detected, typically through a complete blood count with differential, a healthcare provider will evaluate these results in the context of a person’s symptoms and medical history. This comprehensive assessment is important for determining the specific cause and appropriate course of action.