What type of immunity is characterized by the presence of memory cells?

Active immunity is characterized by the presence of memory cells, which are crucial components of the adaptive immune response. When an individual is exposed to a pathogen, their immune system responds by producing specific lymphocytes, including memory T and B cells. These memory cells remain in the body long after the initial infection has been cleared, allowing for a quicker and more robust response if the same pathogen is encountered again. This is the basis of how vaccinations work, as they stimulate the production of memory cells specific to the antigens in the vaccine.

In contrast, innate immunity is the body’s first line of defense against pathogens and does not involve memory cells or a targeted response to specific pathogens. Humoral immunity is a component of the adaptive immune system characterized by the production of antibodies by B cells; while it involves memory cells, it does not encompass the full concept of active immunity, which includes both cellular and humoral immune responses. Non-specific immunity refers to the generalized response mechanisms that do not tailor their activities to specific pathogens, thus lacking the characteristic memory feature. Therefore, the presence of memory cells is best linked to active immunity, making it the correct choice.