A study on the mechanism of interaction of bone marrow-derived immature thymocytes with thymic dendritic cells

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A characteristic disappearance of thymocytes from the cortex of thymus was observed 48 hrs after intraperitoneal injection of cortisone acetate and the same alteration was also observed by radiation with 500rad of X-ray. However, immnosuppressive agents, cyclosporin A and FK 506 did not cause the reduction of the cortical thymocytes, with a slight loss of medullary thymocytes by FK 506. Reduction of the cortical thymocytes resulted in a reduced concentration of IV^3NeuGc-nLc_4Cer and VI^3NeuGc-nLc_6Cer, both of which were the marker gangliosides of cortisone-sensitive cortical thymocytes. At the same time, a significant increase in II^3NeuAc-LacCer, in both total amount and concentartion, was observed in both rabbit and mouse thymuses after cortisone administration. The specific activity of sialyltransferase, with LacCer and CMP-^<14>C-NeuAc as substrates, was the same in the thymus homogenates of cortisone-administered and control mice. Moreover, no difference was observed in the capacity to synthesize II^3NeuAc-LacCer from ^<14>C-ManNAc in the loose thymuses of cortisone-administered and control mice. However, sialyltransferase involved in the synthesis of II^3NeuAc-LacCer with CMP-^<14>C-NeuAc was only detected in the loose thymuses after cortisone-administration, that is, not in the controls, indicating that LacCer on the cell surface is characteristically sialylated by the plasma membrane-associated sialyltransferase only after cortisone administration. Since the cortisone-induced synthesis of II^3NeuAc-LacCer and activation of the sialyltransferase seemed to occur in thymus matrix cells, these observations might be related to the mechanism underlying detachment of cortisone-sensitive lymphocytes from the thymus matrix cells on modification of the lymphocyte receptor molecule.The analogical hormone-dependent regulation of a negative charge was observed in rabbit uterine endometrium after steroid administration.