(anatomy, immunology) Each of the small oval bodies of the lymphatic system, distributed along the lymphatic vessels, that are clustered in the armpits, groin, neck, chest and abdomen. They act as filters, with an internal honeycomb of connective tissue filled with lymphocytes and macrophages that collect and destroy bacteria, viruses and foreign matter from lymph. When the body is fighting an infection, these lymphocytes multiply rapidly and produce a characteristic swelling of the lymph nodes.