<Li> The lymph transports antigen - presenting cells, such as dendritic cells, to the lymph nodes where an immune response is stimulated . </Li> <P> Lymph vessels called lacteals are in the beginning of the gastrointestinal tract, predominantly in the small intestine . While most other nutrients absorbed by the small intestine are passed on to the portal venous system to drain via the portal vein into the liver for processing, fats (lipids) are passed on to the lymphatic system to be transported to the blood circulation via the thoracic duct . (There are exceptions, for example medium - chain triglycerides are fatty acid esters of glycerol that passively diffuse from the GI tract to the portal system .) The enriched lymph originating in the lymphatics of the small intestine is called chyle . The nutrients that are released to the circulatory system are processed by the liver, having passed through the systemic circulation . </P> <P> The lymphatic system plays a major role in body's immune system, as the primary site for cells relating to adaptive immune system including T - cells and B - cells . Cells in the lymphatic system react to antigens presented or found by the cells directly or by other dendritic cells . When an antigen is recognized, an immunological cascade begins involving the activation and recruitment of more and more cells, the production of antibodies and cytokines and the recruitment of other immunological cells such as macrophages . </P> <P> The study of lymphatic drainage of various organs is important in the diagnosis, prognosis, and treatment of cancer . The lymphatic system, because of its closeness to many tissues of the body, is responsible for carrying cancerous cells between the various parts of the body in a process called metastasis . The intervening lymph nodes can trap the cancer cells . If they are not successful in destroying the cancer cells the nodes may become sites of secondary tumors . </P>

Which of the following is the primary function of the lymphatic system