Immune system defenses and dysfunction

Immune system overview and protective role

The immune system is a network of biological systems that protects an organism from disease. It detects and responds to a wide range of threats—including viruses, bacteria, parasites, cancer cells, and foreign objects—by distinguishing them from the body’s own healthy tissues (“self” vs “non-self”). Nearly all organisms have some form of immune defense, though complexity varies across species. Most organisms use layered protection. Physical barriers (like skin and mucous membranes) block pathogen entry; if pathogens breach these barriers, the innate immune system provides an immediate, non-specific response. If needed, the adaptive immune system mounts a tailored, antigen-specific response and builds immunological memory, enabling faster and stronger protection during later encounters with the same pathogen. Dysfunction of immune regulation can lead to disease, including immunodeficiency (recurrent severe infections), autoimmunity (immune attack on self tissues), and inflammatory or cancer-related problems.

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Innate versus adaptive immune subsystems

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