agranulaire

Agranulaire, or agranular in English, is an adjective used in histology and hematology to describe cells or tissues that lack visible cytoplasmic granules under light microscopy. The term is often applied to white blood cells when their cytoplasm does not contain the prominent granules seen in other leukocytes.

In peripheral blood, agranulocytes refer specifically to lymphocytes and monocytes, which are traditionally distinguished from granulocytes (neutrophils, eosinophils, and basophils) that contain cytoplasmic granules. Lymphocytes are typically small to medium in size with a large, round nucleus and scant to moderate cytoplasm. Monocytes are larger and possess a kidney-shaped nucleus with more abundant cytoplasm.

Functions of agranulocytes reflect their roles in the immune system. Lymphocytes mediate adaptive immunity, including B cells that produce antibodies and T cells that regulate immune responses and kill infected cells. Monocytes differentiate into macrophages and dendritic cells, which perform phagocytosis and antigen presentation.

Clinical notes describe a related concept, agranulocytosis, which denotes a severe reduction in granulocytes, especially neutrophils. This condition is distinct from the lack of granules in agranulocytes and is often drug-induced or due to bone marrow failure. Proper terminology emphasizes the difference between cells that lack granules (agranular) and conditions characterized by an absence or depletion of granulocytes.