Which component provides the first line of defense?

Which component provides the first line of defense?

• A. The inflammatory response is the first line of defense.
• B. Antibodies are the first line of defense.
• C. The mechanical and chemical barriers constitute the first line of defense.
• D. Cytotoxic T cells are the first line of defense.

Answer: (C)

The first line of defense is built from mechanical and chemical barriers at the body's surfaces that block pathogens from entering in the first place. The skin and mucous membranes provide a physical shield, and actions like mucociliary clearance and intact epithelial layers help keep invaders out. Chemical barriers, including acidic environments (such as stomach acid) and antimicrobial substances like lysozyme in tears and saliva, further deter or kill microbes at entry points. When these barriers are breached, the body relies on the second line of defense, such as the inflammatory response, to respond to injury, and later on the adaptive immune components like antibodies and cytotoxic T cells.

The first line of defense is built from mechanical and chemical barriers at the body's surfaces that block pathogens from entering in the first place. The skin and mucous membranes provide a physical shield, and actions like mucociliary clearance and intact epithelial layers help keep invaders out. Chemical barriers, including acidic environments (such as stomach acid) and antimicrobial substances like lysozyme in tears and saliva, further deter or kill microbes at entry points. When these barriers are breached, the body relies on the second line of defense, such as the inflammatory response, to respond to injury, and later on the adaptive immune components like antibodies and cytotoxic T cells.