Innate immunity is best described as:

• A. Immunity present from birth
• B. Immunity requiring prior exposure
• C. Adaptive memory-based defense
• D. Vaccine-induced immunity

Answer: (A)

Innate immunity refers to the defenses you’re born with that provide immediate, non-specific protection against a wide range of pathogens. It includes physical barriers like skin and mucous membranes, chemical defenses such as antimicrobial peptides and stomach acid, and cellular responses from neutrophils, macrophages, dendritic cells, and natural killer cells that respond to broad features common to many invaders. This system does not require prior exposure to a specific pathogen and does not develop lasting, specific memory after encounters.

In contrast, immunity that depends on prior contact with a pathogen or a vaccine corresponds to adaptive immunity, which is antigen-specific and builds memory for stronger and faster responses upon re-exposure. Vaccine-induced immunity activates adaptive defenses rather than innate ones.