Downregulation of interleukin-7 and hepatocyte growth factor in the thymic microenvironment is associated with thymus involution in tumor-bearing mice
Changes in the cell population kinetics of the Balb/c mouse thymus were studied (a) during the growth of a syngeneic transplantable sarcoma and (b) following intraperitoneal injection of dexamethasone. The weight of the thymus fell briefly after tumour transplantation, then recovered with overshoot and eventually declined profoundly. After dexamethasone injection the weight of the thymus fell to roughly one-third of its normal value in 36 hr. Similar cytokinetic changes were observed in both sets of experiments; thymic wasting was accompanied by a small increase in thymocyte cell cycle time, a prolongation of the S-phase of the cycle, a marked decrease in the thymocyte cell production rate and a marked reduction in the growth fraction of the thymocyte population in the superficial cortex. It is suggested that thymic atrophy in tumour bearing animals may be a stress phenomenon.