leucocite

Leucocite, known in English as leucocytes or white blood cells, are nucleated cells of the vertebrate immune system found in the blood and lymphoid tissues. They originate from hematopoietic stem cells in the bone marrow and migrate through the bloodstream before moving into tissues where they participate in immune defense and surveillance. In humans, normal total leucocyte counts range approximately from 4,000 to 11,000 cells per microliter, with values varying by age and laboratory methods.

Leucocite populations are typically classified into granulocytes and agranulocytes. Granulocytes include neutrophils, eosinophils, and basophils, distinguished by cytoplasmic granules and staining properties. Agranulocytes comprise lymphocytes and monocytes. Neutrophils are rapid responders to bacterial infection and perform phagocytosis. Monocytes circulate briefly before migrating into tissues to become macrophages or dendritic cells. Lymphocytes cover several lineages: B cells produce antibodies, T cells coordinate cellular immune responses, and natural killer cells target virus-infected or malignant cells. Eosinophils and basophils contribute to responses against parasites and to the regulation of inflammation and allergic reactions.

Leucocite life spans vary by type, from a few hours for some neutrophils to years for certain lymphocytes. Production is regulated by cytokines and growth factors in the bone marrow and lymphoid organs. Abnormal leucocite levels can signal health issues: leucocytosis indicates elevated counts often due to infection or leukemia, while leucopenia denotes reduced counts from bone marrow suppression, severe illness, or certain therapies.