The Immune System’s First Line of Defense: Role of Physical Barriers, Cells, and Microbiota to Protect against Pathogens.

First line of defense

Skin

The first line of defense is the body’s innate, non-specific immune system, which includes physical barriers such as the skin and mucous membranes, as well as various cells and chemicals that help to protect against invading pathogens. The skin, for example, serves as a physical barrier to prevent pathogens from entering the body, while cells such as macrophages and neutrophils can engulf and destroy invading bacteria. Additionally, the body’s natural microbiota, or the normal population of microorganisms living on and within the body, can also help prevent pathogenic organisms from taking hold.

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