Which statement best defines acquired immunity?

• A. Specific against a foreign antigen, result of prior exposure to antigen active or passive
• B. Non-specific defense against pathogens
• C. Immediate inflammatory response by innate immune cells
• D. Involves physical barriers like skin and mucous membranes

Answer: (A)

Acquired immunity is the body's targeted defense against a specific foreign antigen, and it develops with memory so the response is faster if the same antigen is encountered again. It arises after exposure to an antigen, either through the body's own response (active immunity) such as infection or vaccination, or through transfer of antibodies from another source (passive immunity). This combination of specificity and memory—along with the involvement of B and T lymphocytes that tailor the reaction to the particular antigen—distinguishes acquired immunity from non-specific defenses. The other statements describe immediate, non-specific innate defenses like general inflammatory responses or physical barriers such as skin and mucous membranes, which do not capture the antigen-specific, memory-based nature of acquired immunity.