Acquired active immunity occurs when?

• A. Immunity is present at birth.
• B. Antibodies are transferred from another person.
• C. Immunity is temporary from placental transfer.
• D. The body produces antibodies in response to antigens.

Answer: (D)

Acquired active immunity happens when the body's own immune system produces antibodies in response to antigens, such as from infection or vaccination. When a specific pathogen or vaccine introduces an antigen, B cells become activated and differentiate into plasma cells that secrete targeted antibodies. Memory B cells formed during this response stay in the body, providing long-lasting protection and a faster, stronger response if the same antigen is encountered again. This is why vaccines create durable immunity by teaching the immune system to respond without having to suffer the illness firsthand. In contrast, immunity present at birth is not active; it involves innate defenses and, when present, maternal antibodies transferred to the infant, which are passive and temporary.