Lymph nodes play integral roles in both the innate and adaptive immune responses, as they contain different types of immune cells that recognize and eliminate pathogens, abnormal cells, and toxins. Some of the immune and lymphatic functions of lymph nodes are:

Filtering lymph fluid: Lymph fluid is a collection of fluid that drains from the cells and tissues of the body. It contains proteins, minerals, fats, nutrients, white blood cells, damaged cells, cancer cells, bacteria, viruses, and other foreign agents. Lymph fluid flows through the lymphatic vessels and passes through lymph nodes, where it is filtered by specialized cells called lymphocytes and macrophages. These cells trap and destroy the harmful substances and recycle the useful components of the lymph fluid. ^{1 4}

Producing and activating lymphocytes: Lymphocytes are a type of white blood cells that help defend the body against infections and diseases. There are two main types of lymphocytes: B cells and T cells. B cells produce antibodies that bind to specific antigens (molecules that trigger an immune response) and mark them for destruction. T cells can directly kill infected or abnormal cells, or help activate other immune cells. Lymph nodes contain lymphoid tissues that support the production, development, storage, and activation of lymphocytes. Lymphoid tissues are composed of reticular connective tissue that forms a mesh-like structure with spaces called sinuses. The sinuses allow lymph fluid to circulate and come into contact with lymphocytes. Lymphocytes can also migrate between the blood and the lymph nodes through specialized blood vessels called high endothelial venules. ^{2 3}

Generating immune memory: Lymph nodes are also involved in the generation of immune memory, which is the ability of the immune system to remember and respond more quickly and effectively to previously encountered antigens. When lymphocytes encounter an antigen for the first time, they undergo a process called clonal expansion, which means they multiply and differentiate into effector cells and memory cells. Effector cells are responsible for the immediate immune response, while memory cells persist in the lymph nodes and other lymphoid organs for a long time. If the same antigen is encountered again, the memory cells can rapidly reactivate and mount a stronger and faster immune response. This is the basis of vaccination, which exposes the body to a weakened or inactive form of a pathogen to induce immune memory and protection. ^{2 3}