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 the body encounters pathogens like bacteria or viruses. Once activated, B cells differentiate into plasma cells, which produce large quantities of antibodies. These antibodies are proteins that specifically target and neutralize pathogens, helping to protect the body from infections. Plasma cells can live for a long time, providing long-term immunity by remembering past infections and responding more quickly if the same pathogen invades again.