Naltrexone prevents ethanol-induced changes in rat thymus

Ethanol is known to suppress the immune response, but the underlying mechanism accounting for the immunosuppression is not clearly elucidated yet. The purpose of this study was to investigate the effect of a single dose of ethanol on relative proportion of the four major rat thymocyte subsets and possible mechanism of its action. To this end, adult female AO rats were treated with: a) ethanol (2 or 4 g/kg, i.p.), b) naltrexone (5 mg/kg, i.p.) followed 45 min later by ethanol (2 or 4 g/kg, i.p.), c) naltrexone (5 mg/kg, i.p.), or d) only saline. Twenty hours later the rats were sacrificed and the proportion of the four major thymocyte populations defined by expression of CD4 and CD8 molecules was analyzed. Flow cytometric analysis revealed that ethanol evoked a decrease in the percentage of double-positive CD4+CD8+ thymocytes followed by a proportional increase in the percentage of single-positive CD4+CD8- cells. Naltrexone pretreatment prevented the ethanol-induced alterations in thymocyte subsets. The results clearly indicate that ethanol affects the process of intrathymic T-cell maturation. It seems that this effect might be mediated by an opioid-dependent mechanism.