What are Granulocytes

Granulocytes are white blood cells that help the immune system fight off infection. They have a characteristic morphology; having large cytoplasmic granules, that can be stained by basic dyes, and a bi-lobed nucleus. Typically granulocytes have a role both in innate and adaptive immune responses in the fight against viral and parasitic infections.

As part of the immune response, granulocytes migrate to the site of infection and release a number of different effector molecules, including histamine, cytokines, chemokines, enzymes and growth factors. As a result granulocytes are an integral part of inflammation and have a significant role in the eitology of allergies.

Granulocyte Types and Ranges

There are four types of granulocyte; basophils, eosinophils, neutrophils and mast cells. An overview of the function, lineage, development and key markers of each of these cell types can be found by clicking through to the individual pages listed below.


Basophils are the least common type of granulocyte, making only 0.5% of the circulating blood leukocytes. They are involved in a number of functions such as antigen presentation, stimulation and differentiation of CD4+ T cells.


Eosinophils make up approximately 1% of circulating leukocytes. Eosinophils play an important and varied role in the immune responses and in the pathogenesis of allergic or autoimmune disease.


Neutrophils are the most abundant leukocyte found in human blood and form the vanguard of the body’s cellular immune response.

Mast cells

Mast cells are a type of granulocyte whose granules are rich in heparin and histamine. Mast cells are important in many immune related activities from allergy to response to pathogens and immune tolerance.