Lymph nodes play a critical role in the human body's immune system. They act as filters for lymphatic fluid, which carries immune cells, bacteria, and other foreign particles. Lymph nodes are strategically located throughout the body and are sites where immune responses can be initiated. When pathogens are detected, immune cells within the lymph nodes, such as lymphocytes, are activated to respond to the infection. This function of lymph nodes helps to protect the body from disease and maintain overall health. Their swelling can indicate an ongoing infection or immune response.