Infection and Response Practice Test

Active immunity arises when the body's own immune system encounters an antigen and mounts a response, generating specific antibodies and memory cells that stay in the body. This memory makes the protection long-lasting, often for years or a lifetime, because future exposures can trigger a faster and stronger response. A practical example is vaccination or recovering from an infection, which trains the immune system to recognize and fight that pathogen in the future.

Passive immunity, in contrast, is when ready-made antibodies come from another person or animal and are transferred to someone else. It provides immediate protection but is short-lived because those borrowed antibodies are eventually broken down, and no immunological memory is formed. A common example is maternal antibodies passed from mother to fetus through the placenta (and via breast milk) or receiving antibody-containing preparations after exposure.

So the best description emphasizes that active immunity is produced by the body's own response and is long-lasting, while passive immunity is provided by antibodies from another source and is short-term.