What is the primary function of the adaptive immune system?

The primary function of the adaptive immune system is to build immunological memory, which allows the body to respond more effectively to pathogens it has encountered previously. This aspect of the immune system involves the activation and proliferation of lymphocytes, particularly B cells and T cells, which create specific memory cells after an initial infection. When the same pathogen invades again, these memory cells can rapidly mobilize to eliminate the pathogen more efficiently than during the first exposure.

While generating antibodies for pathogens is an important role of the adaptive immune system, it is part of the broader function of developing immunological memory. Immediate responses to pathogens are primarily a characteristic of the innate immune system, which acts quickly and non-specifically upon infection. Similarly, the recognition and elimination of cancer cells may involve adaptive immunity, but this is a subset of its broader role dealing with all pathogens, thus making immunological memory the defining feature of its function.