B lymphocytes, or 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 in the bone marrow and can differentiate into plasma cells that secrete large amounts of antibodies when activated. When B lymphocytes encounter an antigen, which is a substance that triggers an immune response, they can become activated and proliferate. Some of these activated B cells become memory cells, allowing the immune system to respond more quickly if the same pathogen is encountered again in the future.