- Key People:
- Paul Ehrlich
- Sir Peter B. Medawar
- Related Topics:
- antibody
- autoimmunity
- complement
- specific immunity
- rejection
immunity
What are the two main types of biological immunity?
How do phagocytes contribute to immunity?
What role do memory cells play in the immune system?
immunity, in biology, the ability of the body to prevent or defeat infection from invading microorganisms or parasites. This protection relies on the coordinated actions of the immune system.
The body defends itself against infection through two main types of immunity: innate (or natural) and acquired. Innate immunity consists of defense mechanisms present at birth that act against a broad range of infectious agents, regardless of whether the body has encountered them before. The mechanisms include physical barriers, such as the skin, and chemical barriers, such as antimicrobial enzymes in saliva. If infectious agents breach these first lines of defense, they face additional obstacles—substances such as interferons, which inhibit viral growth and help regulate responses to bacterial infection, and specialized immune cells. Phagocytes engulf and destroy invading organisms, while natural killer cells puncture the membranes of infected or foreign cells. However, innate immunity does not produce lasting protection.
Acquired immunity, by contrast, develops in response to exposure to a specific infectious agent or its products. It is stimulated by infection or vaccination and is characterized by the precise recognition of antigens (foreign substances) by B cells and T cells. When innate defenses are not enough, these lymphocytes mount a targeted attack: Cytotoxic (killer) T cells destroy infected or foreign cells, while helper T cells activate B cells, prompting them to multiply and mature into plasma cells that secrete antibodies. These antibodies bind to antigens, marking the invaders for destruction. Importantly, some T and B cells become memory cells, enabling the immune system to respond more rapidly and effectively if the same pathogen is encountered again. For more information on immunity, see immune system.
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