White blood cells macro

White blood cells, also known as leukocytes, are essential immune system cells responsible for defending the body against infections and invading pathogens.

About this subject

White blood cells, or leukocytes, are nucleated blood cells that play a key role in both innate and adaptive immunity. There are five main types: neutrophils, lymphocytes, monocytes, eosinophils, and basophils. Neutrophils are the most abundant, making up 40 to 70% of total white blood cells, and are the first responders to infection sites. Lymphocytes include B cells and T cells, which are responsible for immunological memory. The normal leukocyte count ranges from 4,000 to 11,000 cells per microliter of blood, with increases often seen during infections or inflammation. These cells are produced in the bone marrow from hematopoietic stem cells through hematopoiesis. After maturation, they circulate in the blood and lymphoid tissues. Lifespan varies: neutrophils live only hours to days, while lymphocytes can persist for years. Abnormalities in white blood cell counts are clinically significant. Leukocytosis (elevated count) can indicate bacterial infection, stress, or leukemia. Leukopenia (low count) may occur in viral infections, autoimmune diseases, or after chemotherapy. The term leukocyte comes from Greek leukos (white) and kytos (cell), referring to their pale appearance under a microscope. The discovery of leukocytes is credited to English physician William Hewson in the 18th century, who described them as colorless particles in blood. Later studies, such as Élie Metchnikoff's work on phagocytosis in the late 19th century, laid the foundation for modern immunology.

Frequently Asked Questions

What is the difference between white blood cells and red blood cells?

Red blood cells (erythrocytes) carry oxygen and lack a nucleus, while white blood cells (leukocytes) are nucleated and play a role in immune defense. Leukocytes are less numerous, making up about 1% of blood volume.

How do white blood cells fight infections?

They detect invaders via surface receptors and can phagocytize pathogens (neutrophils and macrophages), release toxic substances (eosinophils), or produce antibodies (B lymphocytes). T lymphocytes directly kill infected cells.

What does it mean to have high or low white blood cell counts?

High white blood cell counts (leukocytosis) may indicate infection, inflammation, stress, or leukemia. Low counts (leukopenia) can be caused by viral infections, autoimmune diseases, bone marrow damage, or effects of medications like chemotherapy.