DECREASED INTERLEUKIN-2 RECEPTOR AND CELL-CYCLE CHANGES IN MURINE LYMPHOCYTES EXPOSED IN-VITRO TO LOW-DOSES OF CADMIUM CHLORIDE

Relationships between in vitro cadmium-related cell cytotoxicity, ultr astructural changes and altered cell cycle were determined at 21-72 h after mitogenic stimulation of C57BL/6 mouse spleen lymphocytes with c oncanavalin A (Con A). Relatively low doses, 0.6-10 mu M cadmium (Cd), added at 4 h after the mitogen activation, induced a significant cell cytotoxicity and reduced the lymphoblastic activity of the cells. Cyt ometric analysis of the lymphoid cell cycle at 72 h revealed that at c oncentrations greater than or equal to 0.6 mu M Cd, the number of cell s arrested in G(0) + G(1) phase increased, whereas the proportions of cells of the S and G(2) + M phases were substantially reduced. Stainin g of cells with fluorescent anti-CD25 monoclonal antibody showed a cad mium-related decreased number and relative mean fluorescence of CD25() cells, demonstrating a decreased level of interleukin-2 receptor (IL -2R). Furthermore, immunogold ultramicroscopic assay was developed for determination of intracellular interleukin-2 (IL-2) in cadmium-treate d lymphocytes. The level of cytoplasmic and nuclear IL-2, localized in situ by colloidal gold ultraimmunocytochemical technique, has been es timated as markedly decreased in cells treated with greater than or eq ual to 1.2 mu M Cd, as compared with the untreated controls. Disorgani zation/fragmentation of mitochondrion cristae and dilatation of cister nae of the Golgi apparatus appeared as the major ultrastructural chang e in 1.2 mu M Cd-treated lymphocytes. Interestingly, addition of cadmi um in the incubation medium, up to 4 h after mitogen activation, also interacted with lymphoproliferative mechanisms of cells in G(0) + G(1) , S and G(2) + M phase. Overall, multiple ultrastructural changes of C d-treated lymphoid cells were clearly related with the reduced cell vi ability and reduced number of activated lymphoblasts.