Innate (nonspecific) immunity includes the external physical and chemical barriers provided by the skin and mucous membranes. Innate immunity, also known as natural or nonspecific immunity, is the first line of defense our body has against infections and foreign invaders. Unlike adaptive immunity, which develops over time after exposure to specific pathogens, innate immunity is present from birth and provides immediate protection.

This essential defense system involves physical barriers, chemical defenses, and cellular components. Physical barriers, such as the skin and mucous membranes, serve as the body’s initial line of defense by preventing pathogens from entering the body. Chemical defenses include enzymes and antimicrobial peptides that can neutralize or destroy invading microorganisms.

Key cellular components of innate immunity include phagocytes, such as neutrophils and macrophages, which engulf and digest pathogens, and natural killer (NK) cells that target infected or cancerous cells. These cells recognize common patterns on the surface of pathogens, known as pathogen-associated molecular patterns (PAMPs), through pattern recognition receptors (PRRs).

Innate immunity acts quickly, providing immediate protection against a wide range of pathogens. It also plays a critical role in shaping the adaptive immune response by presenting antigens to adaptive immune cells. While innate immunity is essential, it has limitations and cannot offer long-term protection against all pathogens. This is where adaptive immunity comes into play, providing a more tailored and specific defense mechanism after exposure to a particular pathogen. It also includes various internal defenses, such as antimicrobial substances, natural killer cells, phagocytes, inflammation, and fever.

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