The carriage and delivery of substances to lymphatic tissues by recirculating lymphocytes. I. The concentration of ricin in lymphocyte traffic areas.

Thoracic duct lymphocytes (TDL) were loaded in vitro with ricin before intravenous injection into syngeneic rats. TDL that had been incubated at 10 micrograms of ricin/5 X 10(7) cells/ml migrated from the blood into the spleen and lymph nodes (LN) according to the physiological pattern, and TDL incubated at 10 times that concentration were only slightly impaired in their ability to enter LN. The transfer of cells to recipients with thoracic duct fistulae indicated that very few ricin-treated lymphocytes left the LN to recirculate back to lymph. Most of the ricin-loaded lymphocytes died within the lymphatic tissues, probably between 7 and 15 hr after injection. The ricin toxicity was transferred locally, causing selective damage to the cell population within the traffic areas of the lymphatic tissues without disrupting the tissue architecture. This pattern of intensive cell destruction was not seen after a lethal dose of free ricin, which caused more diffuse and less severe damage to the spleen and LN, proving that lymphocytes are effective carriers of ricin. The surviving host lymphocytes were distributed abnormally, presumably because of the obvious damage to small blood vessels in LN and elsewhere. Lymphocytes accumulated especially in the red pulp of the spleen. Although the method described has drawbacks, it might be developed in order to concentrate ricin in the vicinity of neoplastic cells in diffuse lymphomas and leukaemias.