granulocite

Granulocyte is a type of white blood cell characterized by the presence of cytoplasmic granules that stain with standard hematologic dyes. They are part of the innate immune system and originate from the myeloid lineage. The term typically refers to three main subtypes: neutrophils, eosinophils, and basophils. In routine blood counts, granulocytes make up a large portion of leukocytes, with neutrophils usually being the most abundant.

Granulocytes develop in the bone marrow through granulopoiesis, guided by growth factors such as granulocyte colony-stimulating factor (G-CSF). After maturation, they enter circulation and can migrate into tissues in response to infection or inflammation. Morphology and staining help distinguish subtypes: neutrophils have a multi-lobed nucleus and neutral granules, eosinophils contain orange-red granules and typically have a bilobed nucleus, and basophils possess large dark granules and a bilobed or S-shaped nucleus.

Functions vary by subtype. Neutrophils are rapid responders that phagocytose and kill invading bacteria and fungi and release reactive oxygen species. Eosinophils defend against parasites and modulate inflammatory and allergic responses. Basophils release histamine, heparin, and other mediators that influence vascular permeability and inflammation. Together, granulocytes participate in early defense, recruitment of other immune cells, and coordination of inflammatory processes.

Clinical relevance is often assessed by granulocyte counts in blood tests. Abnormal numbers can indicate infection, inflammation, bone marrow disorders, or the effects of chemotherapy, while functional defects can occur in certain inherited or acquired conditions.