The lymphatic vascular system is hierarchically divided into lymph capillaries, vessels and trunks, with lymph nodes interposed in the lymphatic vascular system. The lymphatic system forms an extensive network in which the tubes end blindly. The main functions of the lymphatic system include the absorption of interstitial fluid and its return to the bloodstream, the transport of fats absorbed in the intestine into the blood, and the transport of immune cells, pathogens and other immunogenic substances. Although lymphatic capillaries are closed, they are permeable to dissolved fats, proteins, microorganisms and foreign substances in the interstitium (space between organs). When fluid enters the lymphatic capillaries from the interstitium, it is called lymph. The transport pathway from the interstitium to the lymph capillaries provides a functional drainage system and contributes to the regulation of local fluid balance. The lymph nodes are intermediate filter stations in the lymphatic vascular system, in which lymphocytes are located that are searching for antigens. Important detection markers for lymphocytes, such as T and B lymphocytes, are CD43, CD8 and CD21.