The lymphatic system is made up of lymph nodes and lymph vessels (lymphatic) that link the lymph nodes. The nodes make a type of white blood cell (lymphocytes) that fights infections. When an infection is present, the lymph nodes swell, produce white blood cells, and attempt to trap the organisms that are causing the infection. The lymph nodes also try to trap cancer cells. In this test, a lymph node or a piece of a lymph node is removed for examination under a microscope.