The nuclear I kappa B protein I kappa B-zeta is barely detectable in resting cells and is induced in macrophages and fibroblasts following stimulation of innate immunity via Toll-like receptors. The induced I kappa B-zeta associates with nuclear factor (NF)-kappa B in the nucleus and plays crucial roles in its transcriptional regulation. Here, we examined the induction of I kappa B-zeta in B lymphocytes, one of the major players in adaptive immunity. Upon crosslinking of the surface immunoglobulin complex, I kappa B-zeta mRNA was robustly induced in murine B-lymphoma cell line A20 cells. While the crosslinking activated NF-kappa B and induced its target gene, I kappa B-alpha, co-crosslinking of Fc gamma receptor 1113 to the surface immunoglobulin complex inhibited NF-kappa B activation and the induction Of I kappa B-zeta and I kappa B-alpha, suggesting critical roles for NF-kappa B in the induction. These results indicate that IKB-zeta is also induced by stimulation of B cell antigen receptor, suggesting that I kappa B-zeta is involved in the regulation of adaptive immune responses. (c) 2007 Elsevier Inc. All rights reserved.