whitecell

White cells, or white blood cells (WBCs), are a key component of the circulatory and immune systems. They are produced in the bone marrow from hematopoietic stem cells and circulate in the bloodstream and lymphatic system, migrating to tissues where they are needed. In contrast to red blood cells, white cells are nucleated and far fewer in number, but they mediate targeted defense against pathogens and damaged cells.

White blood cells are divided into two broad categories: granulocytes, which include neutrophils, eosinophils, and basophils; and agranulocytes, consisting of lymphocytes and monocytes. Neutrophils respond rapidly to infection, chiefly by phagocytosing bacteria and releasing antimicrobial substances. Lymphocytes include B cells, which produce antibodies; T cells, which coordinate immune responses and kill infected cells; and natural killer cells, which destroy abnormal cells. Monocytes circulate in blood and differentiate into macrophages or dendritic cells in tissues, where they phagocytose pathogens and present antigens to other immune cells. Eosinophils help fight parasites and modulate allergic reactions, while basophils contribute to inflammation and hypersensitivity by releasing histamine and other mediators.

White blood cell counts are a common clinical measure; normal adult ranges are typically about 4,000 to 11,000 cells per microliter, though exact values vary by lab and age. Elevated counts, or leukocytosis, can indicate infection, inflammation, or bone marrow disorders; low counts, or leukopenia, can reflect bone marrow suppression, autoimmune disease, or certain medications. Abnormal WBC patterns may prompt further testing to identify specific causes, such as a bacterial or viral infection, immune deficiency, or hematologic disease.