granulocytic

Granulocytic is an adjective used to describe anything relating to granulocytes, a class of white blood cells characterized by cytoplasmic granules. In humans, the main granulocytic lineages are neutrophils, eosinophils, and basophils, all derived from hematopoietic stem cells in the bone marrow through a process called granulopoiesis. Some discussions of development also address the immature precursors such as promyelocytes and myelocytes.

Function and morphology: Neutrophils are the most abundant granulocytes and act as first responders to infection, performing phagocytosis and releasing antimicrobial substances. Eosinophils combat parasitic infections and participate in allergic and inflammatory responses. Basophils release histamine and other mediators that influence vascular permeability and immune signaling. All three types contain cytoplasmic granules that contribute to their microbicidal and inflammatory roles.

Development and regulation: Granulopoiesis is regulated by cytokines, notably granulocyte colony-stimulating factor (G-CSF) and granulocyte-macrophage colony-stimulating factor (GM-CSF), which promote the production, maturation, and function of granulocytes. Abnormal granulocyte levels can occur in various conditions, including neutropenia (low neutrophils) and neutrophilia (high neutrophils), often reflecting infection, inflammation, or bone marrow disorders.

Clinical relevance: In laboratory medicine, granulocytic refers to properties or processes involving granulocytes, and differential white blood cell counts report the proportions of neutrophils, eosinophils, and basophils. Granulocytic proliferation is a feature of several myeloid disorders, such as myeloproliferative neoplasms and acute or chronic leukemias. Rarely, tumors composed of granulocytic precursors outside the marrow—granulocytic sarcomas (chloromas)—are described.