How do vaccines evoke an immune response?

Vaccines are designed to stimulate the immune system by introducing an antigen, which is a component of the pathogen that causes disease, into the body. This antigen is recognized by the immune system as foreign, which activates B cells, a type of white blood cell crucial for producing antibodies. When B cells encounter the antigen, they start to proliferate and differentiate into plasma cells that produce antigen-specific antibodies. These antibodies help neutralize or eliminate the pathogen.

In addition to producing antibodies, the activation of B cells also leads to the formation of memory B cells. These memory cells remain in the body long after the initial exposure and provide long-term immunity. If the individual is exposed to the actual pathogen in the future, these memory cells can quickly respond by producing antibodies, thereby enhancing the body's immune response more rapidly and effectively than it would without prior exposure.

This mechanism is central to how vaccines confer immunity, allowing for a protective response without causing the disease itself. Thus, the answer correctly highlights the dual role of B cells in producing both antibodies and memory cells, fundamental components of a successful immune response elicited by vaccines.