What is one characteristic of the adaptive immune system?

The characteristic of the adaptive immune system that stands out is its ability to remember previous infections. This feature is primarily due to the presence of memory B and T cells that are formed after the initial exposure to a pathogen. Upon subsequent exposures to the same pathogen, these memory cells enable the adaptive immune system to mount a faster and more efficient response, often neutralizing the pathogen before it can cause significant harm.

This memory is a crucial aspect of vaccinations, which aim to elicit a response that prepares the immune system for future encounters with specific pathogens. In contrast, the innate immune system provides an immediate but nonspecific defense against pathogens, lacking the memory component and specificity of the adaptive immune system. The adaptive immune system does not activate solely during viral infections, as it can respond to a variety of pathogens, including bacteria and parasites, and it is not found in all living organisms—some simpler organisms rely on innate immunity only.