The lymphatic system is a network of tissues and organs. It is made up mainly of lymph vessels, lymph nodes and lymph. Lymph vessels, which are different from blood vessels, carry fluid called lymph throughout your body. Lymph contains white blood cells that defend you against germs. Throughout the vessels are lymph nodes. Along with your spleen, these nodes are where white blood cells fight infection. Your bone marrow and thymus produce the cells in lymph. They are part of the system, too. The lymphatic system clears away infection and keeps your body fluids in balance. If it's not working properly, fluid builds in your tissues and causes swelling, called lymphedema. Other lymphatic system problems can include infections, blockage, and cancer .