Leukocyttyper

Leukocyttyper, or leukocyte types, are the major categories of white blood cells in humans. They circulate in the blood and reside in lymphoid and other tissues as part of the immune system. Leukocytes originate from hematopoietic stem cells in the bone marrow and differentiate along two main lineages: the myeloid lineage, giving rise to neutrophils, eosinophils, basophils, and monocytes; and the lymphoid lineage, which produces lymphocytes (B cells, T cells, and NK cells).

Neutrophils are the most abundant and are rapid responders that perform phagocytosis to destroy invading bacteria. Lymphocytes mediate adaptive immunity; B cells produce antibodies, T cells coordinate cellular responses, and NK cells target virus-infected or malignant cells. Monocytes circulate as precursors that migrate into tissues to become macrophages or dendritic cells, which ingest pathogens and present antigens. Eosinophils help combat parasites and modulate allergic reactions. Basophils release mediators such as histamine during inflammation and allergic responses.

Clinical leukocyte typing is usually provided as a differential white blood cell count, combining relative percentages with absolute counts. Modern automated analyzers classify cells by size, granularity, and staining, while manual examination of stained smears remains a reference method in some settings. Abnormal leukocyte patterns can indicate infection, inflammation, allergy, hematologic disorders, or immune dysfunction and guide further testing.

Typical adult ranges (percent of total white cells) are approximately neutrophils 40–60%, lymphocytes 20–40%, monocytes 2–8%, eosinophils 1–4%, and basophils 0.5–1%. Note that reference values vary by laboratory, age, and population. Understanding leukocyte types supports assessment of immune status and diagnosis of related conditions.