Final answer:
Memory B cells respond rapidly and produce antibodies to fight against the pathogen.
Step-by-step explanation:
In the scenario where the primary immune response declines and you are susceptible to infection by the same pathogen, Memory B cells respond rapidly. Memory B cells retain the information about the particular pathogen from the previous exposure. When the pathogen is encountered again, the memory B cells quickly differentiate into plasma cells that produce antibodies to fight against the pathogen, providing a stronger and more rapid immune response compared to the primary response.