An essential role for nuclear factor κB in promoting double positive thymocyte apoptosis

To examine the role of nuclear factor (NF)-kappa B in T cell development and activation in vivo, we produced transgenic mice that express a superinhibitory mutant form of inhibitor kappa B-alpha (I kappa B-alpha(A32/36)) under the control of the T cell-specific CD2 promoter and enhancer (mutant [m]I kappa B-alpha mice). Thymocyte development proceeded normally in the mI kappa B-alpha mice. However, the numbers of peripheral CD8(+) T cells were significantly reduced in these animals. The mI kappa B-alpha thymocytes displayed a marked proliferative defect and significant reductions in interleukin (IL)-2, IL-3, and granulocyte/macrophage colony-stimulating factor production after cross-linking of the T cell antigen receptor. Perhaps more unexpectedly, double positive (CD4(+)CD8(+); DP) thymocytes from the mI kappa B-alpha mice were resistant to alpha-CD3-mediated apoptosis in vivo. In contrast, they remained sensitive to apoptosis induced by gamma-irradiation. Apoptosis of wild-type DP thymocytes after in vivo administration of alpha-CD3 mAb was preceded by a significant reduction in the level of expression of the antiapoptotic gene, bcl-x(L). in contrast, the DP mI kappa B-alpha thymocytes maintained high level expression of bcl-x(L) after alpha-CD3 treatment. Taken together, these results demonstrated important roles for NF-kappa B in both inducible cytokine expression and T cell proliferation after TCR engagement. In addition, NF-kappa B is required for the alpha-CD3-mediated apoptosis of DP thymocytes through a pathway that involves the regulation of the antiapoptotic gene, bcl-x(L).