Granulocytes

Granulocytes are leukocytes with multilobed nuclei and small, enzyme-containing granules in their cytoplasm that are released in response to microbial infections. They can be categorized as either neutrophils, eosinophils, basophils, or mast cells. All of these are terminally differentiated cells that develop in the bone marrow and function primarily as part of the innate immune response, although they may also have antigen-presenting capabilities. Neutrophils are the most abundant type of leukocytes, accounting for approximately 50-70% of leukocytes in the blood. They are professional phagocytes and play a central role in the immune response to bacterial infections. Eosinophils are a minor population of circulating leukocytes (<5%), with larger numbers being found in some tissues. Eosinophils are particularly important for combating helminth infections and allergens through the release of cationic proteins and cytokines contained within their granules. Like eosinophils, mast cells and basophils are also thought to be involved in type 2 immune responses mounted against multicellular parasites and allergens. Both basophils and mast cells are rare cell types that release effector molecules stored in their cytoplasmic granules following activation induced by IgE-Fc epsilon RI receptor cross-linking. While these cells have beneficial protective effects, they may also contribute to detrimental inflammatory responses and autoimmune diseases.