Augmentation of lipopolysaccharide-induced thymocyte apoptosis by interferon-gamma

The role of interferon (IFN)-gamma on thymocyte apoptosis in response to lipopolysaccharide (LPS) was investigated. The administration of LPS into mice induced marked apoptosis of thymocytes in vivo, but the simultaneous injection of anti-IFN-gamma antibody with LPS completely prevented thymocyte apoptosis. Pretreatment of mice with IFN-gamma markedly enhanced LPS-induced thymocyte apoptosis. Thymocyte apoptosis augmented by IFN-gamma occurred in the thymic cortex, and target cells undergoing apoptosis were CD4+8+ immature thymocytes. IFN-gamma itself did not induce thymocyte apoptosis in vivo and in vitro. IFN-gamma exhibited no synergistic action with effector molecules, such as tumor necrosis factor (TNF)-alpha and glucocorticoids. Further, it was shown that IFN-gamma did not enhance the susceptibility of thymocytes to apoptosis. Pretreatment of mice with IFN-gamma significantly augmented the serum TNF-alpha level and the serum cortisol level in response to LPS. Therefore, we suggest that IFN-gamma might augment LPS-induced thymocyte apoptosis through elevating serum TNF-alpha and cortisol levels.