Lymphocytes are a type of white blood cell that play a crucial role in the immune system. They help the body fight off infections and diseases by recognizing and attacking harmful invaders like bacteria and viruses. There are two main types of lymphocytes: B cells, which produce antibodies, and T cells, which destroy infected or cancerous cells. These cells are produced in the bone marrow and mature in different parts of the body, such as the thymus for T cells. Lymphocytes circulate through the bloodstream and lymphatic system, constantly monitoring for threats to keep the body healthy and protected.