Final answer:
The longest duration of antibodies comes from those produced by memory cells in the secondary immune response, particularly IgG, which persists longer in the serum after antigen exposure.
Step-by-step explanation:
The longest duration of action for antibodies comes from those produced by memory cells during the secondary immune response. After the first exposure to an antigen, there is an initial lag period followed by a primary antibody response with a rise in IgM levels. As the exposure continues or is repeated, there is a process called class switching, and antibodies of the IgG class increase, which tend to persist for a longer period of time in the serum after antigen exposure. Memory cells, created after this first exposure, later differentiate into antibody-secreting plasma cells that secrete a greater amount of antibody during re-exposure, thus providing a longer duration of protection. Passive immunity, which involves the transfer of antibodies from one individual to another, can offer temporary protection but does not last as long as the active immunity generated by an individual's own immune system after exposure to an antigen.