Plasma cells are a type of white blood cell that play a crucial role in the immune system. They are derived from B cells, which are activated when they encounter specific pathogens. Once activated, B cells differentiate into plasma cells, which produce large quantities of antibodies to help neutralize infections. These antibodies are proteins that specifically target and bind to antigens, which are foreign substances like bacteria and viruses. Plasma cells can produce thousands of antibodies per second, providing a strong defense against infections. They are essential for the body's ability to remember and respond to previously encountered pathogens, contributing to long-term immunity.