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How does the immune system protect the body against pathogens?

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The human immune system protects the body through a coordinated defense involving two primary strategies: innate and acquired immunity.1

Innate Immunity

Innate immunity provides immediate, non-specific protection present from birth. It includes:1
* Physical and Chemical Barriers: The skin acts as a primary barrier, while substances like saliva contain antimicrobial enzymes.1
* Specialized Cells: Phagocytes (such as granulocytes and macrophages) scout for and ingest invaders, while natural killer cells destroy infected or foreign cells.213
* Proteins: Substances like interferons inhibit viral growth, and the complement system can damage the membranes of invading cells.13

Acquired Immunity

When innate defenses are insufficient, the body mounts a targeted response involving lymphocytes (T cells and B cells).1
* Targeted Attack: B cells produce antibodies that bind to specific antigens, neutralizing toxins or marking pathogens for destruction.413
* Memory: Some T and B cells become memory cells, allowing the immune system to recognize and respond more rapidly if the same pathogen is encountered again.15

These processes are supported by the lymphatic system, which serves as a site for lymphocyte production and a network for detecting pathogens.26