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How does the body defend itself against bacteria and viruses?

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The human body defends itself against bacteria and viruses through a sophisticated, two-tiered immune system consisting of innate and acquired immunity.1

Innate Immunity

This is the body's first line of defense, present from birth to provide immediate, broad protection.1
* Physical and Chemical Barriers: The skin acts as a mechanical barrier, while secretions like saliva and tears contain enzymes such as lysozyme that break down bacterial walls.12
* Cellular Response: Phagocytes (such as neutrophils and macrophages) engulf and destroy invaders. Natural killer cells target infected cells, and interferons help inhibit viral growth.13
* Inflammation: Tissue damage triggers an inflammatory response, increasing blood flow and bringing more immune cells to the site of infection.4

Acquired Immunity

If innate defenses are breached, the body mounts a targeted response.1
* Lymphocytes: B cells and T cells recognize specific antigens.1
* Antibodies: B cells mature into plasma cells that secrete antibodies, which bind to and neutralize pathogens.15
* Memory: Some cells become memory cells, allowing the body to respond more rapidly if the same pathogen is encountered again.16