B cells are a type of white blood cell that play a crucial role in the immune system. They are responsible for producing antibodies, which are proteins that help identify and neutralize pathogens like bacteria and viruses. B cells originate from stem cells in the bone marrow and mature there before entering the bloodstream. When B cells encounter a specific antigen, which is a substance that triggers an immune response, they can differentiate into plasma cells. These plasma cells produce large quantities of antibodies tailored to that antigen. This process is essential for the body's ability to remember and respond more effectively to future infections by the same pathogen, a phenomenon known as immunological memory.