Lymphocytes are a type of white blood cell that play a crucial role in the immune system. They help the body fight infections and diseases by identifying and attacking harmful pathogens, such as bacteria and viruses. There are three main types of lymphocytes: B cells, T cells, and natural killer (NK) cells, each with specific functions in immune response. B cells produce antibodies that target specific antigens, while T cells help regulate immune responses and directly kill infected cells. Natural killer cells provide a rapid response to virally infected cells and tumors. Together, these lymphocytes work to maintain the body's defense against various threats.