Final answer:
The immunity that develops over time due to antigen exposure is known as acquired immunity. It involves a specific adaptive response, comprising both humoral and cellular immunity, and allows for a quicker and more potent response upon subsequent exposures to the pathogen.
Step-by-step explanation:
Immunity that develops over time and results from exposure to an antigen is called acquired immunity. This form of immunity occurs after exposure to an external threat, such as a pathogen or a vaccine, and it consists of both humoral and cellular responses. When a pathogen invades the body, it triggers the adaptive immune system, after which memory B cells and T cells remain that provide a memory of the pathogen, ensuring a quicker and more effective response upon re-exposure.
There are different ways of acquiring immunity. Natural active immunity developed after an actual infection is an example of such a process, with memory cells enabling long-term protection. In the context of vaccinations, the type of immunity we're referring to is artificially acquired active immunity.