When sickness or infection invades the body, the immune system is the first line of defense. A big part of that defense is the lymph system.
lymph is a transparent fluid containing white blood cells, which help fight infection. The main types of white blood cells are lymphocytes. lymph is carried through the body by lymph vessels that have valves and muscles to help move the fluid. Along the route are lymph nodes that serve as filters for harmful substances. This network of vessels and lymph nodes together is called the lymph system.