CD4 and Atrophy: Oral administration of tributyltinacetate resulted in a decrease in CD4 and CD8 SP T-cell populationsand blocked the thymocyte differentiation at the DP and DN stagesby down-regulating IL-7 mRNA in thymic epithelial cells.64,65 During severe thymic atrophy induced by dexamethasone or irradiation,the regeneration of the thymus occurred through upregulation of IL-7expression.66 Collectively, these datasuggest that the regulation of IL-7 plays a crucial role in compensatingfor different chemical stimuli.