What is the first line of defense in the body's immune system?

The first line of defense in the body's immune system is comprised of the skin and mucous membranes. These structures serve as the initial physical and chemical barriers that protect the body from pathogens such as bacteria, viruses, and fungi. The skin, being a tough outer layer, prevents direct entry of microbes, while mucous membranes line the respiratory, gastrointestinal, and urogenital tracts, trapping pathogens and facilitating their removal through various mechanisms, including ciliary action and mucus secretion.

Additionally, the skin produces antimicrobial peptides and secretes substances like sweat and oil that can inhibit microbial growth. Mucous membranes also produce mucus, which contains enzymes and antibodies that attack pathogens, making these barriers crucial for the body's defense before the immune system engages its more complex components like white blood cells or antibodies. Therefore, the skin and mucous membranes are fundamental for preventing infection and maintaining overall health.