The presence of which cells forms the basis of immunity?

Memory cells are crucial to the immune system as they provide the foundation for long-term adaptive immunity. These cells are formed after an initial exposure to an antigen, and their primary role is to "remember" that specific antigen for future encounters. When the body encounters the same pathogen again, memory cells rapidly proliferate and differentiate into effector cells, allowing for a swift and effective immune response.

This characteristic of memory cells transforms the immune system from a naive state to one that is prepared for reinfection, significantly improving the body's efficacy in combating previously encountered pathogens. The existence of memory cells is why vaccinations can provide lasting protection against certain diseases, illustrating their essential role in the overall immunity framework. Other immune cells, such as cytotoxic T-cells, helper T-cells, and B-lymphocytes, also play important roles in the immune response but do not have the same long-term memory function essential for establishing immunity.