The defining characteristic of innate immunity - it:

• A. Is learned and adaptive
• B. Requires prior exposure
• C. Is inborn and congenital
• D. Depends on antibodies

Answer: (C)

Innate immunity is the body's built-in, non-specific defense that you’re born with and that acts immediately against a wide range of pathogens. It doesn’t require previous exposure or learning, and it doesn’t rely on antibodies. That’s why the defining characteristic is that it’s inborn and congenital.

In contrast, adaptive immunity is specific, develops after exposure to a particular pathogen, and uses antibodies and memory to provide targeted, long-lasting protection. The innate system uses general barriers like skin and mucous membranes, phagocytes such as neutrophils and macrophages, natural killer cells, and the complement system to provide rapid early defense.