Swellings which occur at various points in the lymphatic system through which LYMPH drains. They have two main functions: (1) the interception and removal of abnormal or foreign material from the lymph; (2) the production of immune responses (see IMMUNITY). The lymph nodes become enlarged when the area of the body which they drain is the site of infection or as a manifestation of some systemic diseases. Occasionally they are the site of primary or metastatic malignant disease.