Final answer:
Humoral immunity, mediated by B lymphocytes, involves the production of specific antibodies that bind to antigens on pathogens. Once bound, these antibodies signal phagocytes to destroy the pathogens. B cells mature in bone marrow, differentiate into plasma cells upon activation, and operate primarily in blood and lymph.
Step-by-step explanation:
Humoral immunity is principally conducted through B lymphocytes (B cells), which create antibodies to combat extracellular pathogens and toxins. These B cells emerge from hematopoietic stem cells in the bone marrow and mature there, distinct from T cells which mature in the thymus. B cells produce antibodies, large Y-shaped proteins that can specifically bind to antigens found on foreign microbes. Antigens are recognized as foreign to stimulate an immune response. Upon binding to antigens, antibodies act as a flag that prompts phagocytes, a type of white blood cell, to engulf and destroy the pathogens they are attached to in a process known as phagocytosis.
In additional roles, B cells may also present antigens to T cells and secrete cytokines to aid in orchestrating the immune response. Once a B cell is activated by an antigen, it differentiates into plasma cells, which are B cells specialized for the secretion of antibodies. These plasma cells provide the primary mechanism of humoral immunity, defending against pathogens in bodily fluids like blood and lymph.