Glucocorticoid and mitogen sensitivity of rat splenic and thymic lymphocytes in vitro after in vivo cyclophosphamide treatment.

that may arise as a result of combined therapy have not yet been fully researched and understood. This study examines the sensitivity of splenic and thymic lymphocytes to gluco corticoids and mitogens in vitro following in vivo treatment of animals with CY. CY is used in immunosuppression as well as cancer therapy (6). It has found application particu larly for acute and chronic lymphocytic leukemia, multiple myeboma, and lymphomas. CY is metabolized to the active phosphoramide mustard by hepatic microsomal enzymes (2), and most of its cytotoxic effects are believed to result from disruption of DNA synthesis that is due to the forma tion of guanine cross-bridges (6). CY is therefore most efficient in inhibiting the growth of rapidly dividing cells. Lymphoid cells are particularly responsive to CY with a 60 to 70% depletion of lymphoid organ lymphocytes observed within 1 day after CY and 95% depletion observed within 3 days in the mouse (17). Recovery of lymphoid cells in the spleen was observed within 7 days after 1 CY injection (17). Turk and Poulter (16) observed that a selective depletion of B-cells occurs following CY. Recent reports, however, sug gest effects on T-cells specifically, with selective cytotoxic ity towards T-suppressor and T-hebper subpopulations (1, 17). Milton et a!. (1 0) reported decreased T-cell cytotoxicity with prolonged skin graft survival in mice. In addition to a depletion in Band T-cells, CY in vivo diminishes the ability of cells to synthesize DNA in response to T-ceIl mitogens such as concanavalin A and phytohemagglutinin (5, 10). Dumont and Barrois (5) ascribe this decreased responsive ness to a damaged mitotic apparatus or a less responsive subpopulation to T-cells. Glucocorticoids are used as antimnfbammatory;antitumor, and immunosuppressive agents and their applicability in cancer treatment corresponds to the presence of specific steroid hormone receptors in the cancerous cells (6). Glu cocorticoids also protect against thrombocytopenia, he molytic anemia, and bone marrow depletion that are caused by other methods of chemotherapy. Glucocorticoids inter act initially with cytoplasmic receptors and subsequently undergo a temperatureand energy-dependent activation and transbocation of the steroid:receptor complex to the nucleus. Supposedly, the nuclear accumulation of steroid:receptor complexes results in mRNA synthesis which allows for the production of proteins and hormonal effects (8, 9, 12, 13). In lymphoid cells these effects include inhibition of glucose, decreased RNA synthesis, decreased protein synthesis, increased nuclear fragility, and cell death. The data in this study show that treatment of animals With CY diminishes the ability of the remaining splenic and thymic lymphocytes to respond to glucocorticoids in vitro. This effect appears to be mediated by loss in both cytoplas mic and nuclear hormone receptor binding capacity. ABSTRACT