granulocytesneutrophils

Granulocytes are a class of white blood cells characterized by the presence of cytoplasmic granules. They arise from hematopoietic stem cells in the bone marrow through myelopoiesis and are classified into three main types: neutrophils, eosinophils, and basophils. Each type has distinct morphology and functions, contributing to the body's defense against infection and to inflammatory and allergic responses.

Neutrophils are the most abundant circulating leukocytes and are among the first cells to reach sites of infection. They are typically multi-lobed and employ phagocytosis, degranulation, and the respiratory burst to kill bacteria and fungi. They have a relatively short lifespan in blood and tissues and are continually renewed by bone marrow production driven by colony-stimulating factors.

Eosinophils combat multicellular parasites and participate in modulating allergic inflammation. They release cytotoxic granule proteins and reactive oxygen species, and they can interact with other immune cells to shape immune responses. Basophils, the least common granulocytes in the circulation, contain granules rich in histamine and heparin and contribute to inflammatory and allergic reactions by releasing mediators upon activation.

Granulopoiesis is regulated by growth factors such as granulocyte colony-stimulating factor (G-CSF) and granulocyte–macrophage colony-stimulating factor (GM-CSF). Clinically, granulocyte counts are part of the complete blood count; abnormal levels can indicate infection, inflammation, hematologic disorders, or immune dysfunction. Together, granulocytes play essential roles in innate immunity, host defense, and the regulation of inflammatory processes.