Final answer:
The immune response in which B cells transform into plasma cells and secrete antibodies is called active immunity. It is the body's own immune system's response to pathogens or vaccines, as opposed to passive immunity, where antibodies are acquired from an external source.
Step-by-step explanation:
An immune response in which B cells transform into plasma cells and secrete antibodies is known as active immunity. This type of immunity describes the body's own immune system actively responding to an infection or vaccination by producing antibodies. In contrast, passive immunity involves receiving antibodies from an external source, for instance, through maternal antibodies crossing the placenta or through injection of antivenoms.
Upon encountering a pathogen, the adaptive immune system is informed by the innate immune system and sets off a series of events. Helper T cells stimulate B cells that have presented pathogen-derived antigens. The B cells then differentiate into plasma cells which secrete large amounts of antibodies specific to the antigen. These antibodies circulate freely and are essential agents in the humoral immune response, battling extracellular pathogens and toxins. Additionally, memory B cells are produced, which can quickly respond to subsequent exposures to the same pathogen.
In the context of immunity, it's important to recognize the distinction between active and passive immunity, as both play critical roles in protection against diseases. While active immunity is a result of the body's own immune response, passive immunity provides immediate, but temporary protection by introducing external antibodies.