Why in inflammatory and infectious conditions may clinical signs related to the lymphatic system occur?

The lymph nodes, or lymph glands, have lymphoid tissue that makes lymphocytes (a type of leukocyte). In inflammatory and infectious conditions the enlargement of lymph nodes of the lymphatic circuits that drain the affected region because of the reactive proliferation of leukocytes is common. This enlargement is called as lymphadenomegaly and sometimes it is accompanied by pain. The search for enlarged or painful lymph nodes is part of the medical examination since these findings might be suggest inflammation, infection or other diseases.

The Circulatory System - Image Diversity: lymphadenopathy