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How do white blood cells defend the body against infections and disease?

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Illustration of a blood vessel with a cutaway view showing red blood cells, white blood cells, platelets, and plasma, each labeled to highlight the main components of blood. — white blood cell Blood is made up of multiple components, including red blood cells, white blood cells, platelets, and water-rich plasma.

White blood cells, or leukocytes, defend the body against infection and disease through several specialized mechanisms, primarily categorized by their cell type.12

Phagocytosis

Granulocytes—specifically neutrophils—and monocytes (which mature into macrophages) act as the body's primary phagocytes. These cells migrate to sites of infection or injury, where they ingest and digest bacteria, foreign particles, and cellular debris. Neutrophils are typically the first to arrive, while macrophages are larger, longer-lived scavengers that also play a role in activating the acquired immune response by presenting antigens to other cells.3421

Immune Response

Lymphocytes are responsible for specific recognition and removal of foreign agents. They function through two main pathways:52
* Humoral Immunity: B cells secrete antibodies that bind to foreign microorganisms, marking them for destruction or preventing reinfection.16
* Cell-Mediated Immunity: T cells perform surveillance, identifying and destroying virally infected or cancerous cells, and assisting B cells in antibody production.26

These cells work in concert to maintain health, with their activity often resulting in inflammation as they accumulate at sites of damage to neutralize threats.31