Which components of the immune system are characteristic of innate immunity?

• A. Barriers, phagocytes, NK cells
• B. Antibodies and memory
• C. B and T lymphocytes
• D. Plasma proteins and complement only

Answer: (A)

Innate immunity is the body's immediate, non-specific defense, built from physical barriers and early responders that act without prior exposure. The best answer includes barriers, phagocytes, and natural killer cells. Barriers like skin and mucous membranes block entry; phagocytes such as neutrophils and macrophages engulf and destroy invading microbes; natural killer cells detect and kill infected or abnormal cells rapidly.

Antibodies and memory characterize adaptive immunity, which is specific and builds over time through B and T lymphocytes, producing targeted responses and lasting memory after exposure. B and T lymphocytes are the hallmark of the adaptive system, not the innate. Plasma proteins and complement are part of innate defenses, but focusing on “plasma proteins and complement only” omits key innate cellular components (and can blur where adaptive antibodies fit in), so it isn’t a complete description of innate immunity.