What is a luekocyte?

Leukocyte, also called white blood cell, any of several types of blood cells that are involved in the body's defense mechanism. Although leukocytes are normally present in the bloodstream, their numbers increase dramatically in response to infection, inflammation, or tissue damage.

Leukocytes are produced in the bone marrow and are transported throughout the body in the blood and lymph. They are classified into two broad categories: granulocytes and agranulocytes. Granulocytes (neutrophils, eosinophils, and basophils) are characterized by the presence of granules in their cytoplasm. Agranulocytes (lymphocytes and monocytes) do not contain granules.

Neutrophils are the most abundant type of leukocyte, making up 50% to 70% of all white blood cells. They are phagocytic, which means that they can engulf and destroy foreign particles. Neutrophils are also involved in the inflammatory response.

Eosinophils make up 1% to 3% of all white blood cells. They are involved in the defense against parasitic infections and allergies. Eosinophils also release chemicals that can damage tissue, contributing to the inflammation that occurs in asthma and other allergic reactions.

Basophils make up less than 1% of all white blood cells. They are involved in the inflammatory response and in the release of histamine, a chemical that causes blood vessels to dilate and leak fluid.

Lymphocytes are the second most abundant type of leukocyte, making up 20% to 30% of all white blood cells. Lymphocytes are divided into two main types: B cells and T cells. B cells produce antibodies, which are proteins that help the body recognize and destroy foreign invaders. T cells help to kill infected cells and regulate the immune response.

Monocytes make up 5% to 10% of all white blood cells. They are phagocytic and can engulf and destroy foreign particles. Monocytes also differentiate into macrophages, which are cells that are found in tissues and that play a role in the inflammatory response.