What does acquired immunity involve?

Acquired immunity is a form of immunity that is not present at birth but develops as a result of exposure to pathogens or through vaccinations. This type of immunity occurs when the immune system recognizes and remembers specific pathogens after an infection or immunization, allowing it to respond more effectively if the body encounters the same pathogen again in the future.

When a person contracts a disease, their immune system mounts a response to fight the infection, leading to the production of memory cells. These cells "remember" the pathogen, providing long-lasting protection. Similarly, vaccinations introduce a harmless part of the pathogen or a weakened version, training the immune system without causing the disease, hence providing immunity against the real pathogen in the future.

The other options refer to types of immunity that are either innate (something that is present from birth) or do not involve the immune system's adaptive response, which does not align with the definition of acquired immunity.