One of the most challenging issues of anti-inflammatory gene therapy is the complexity of inflammatory pathways. Transcription factor NF-κB plays a pivotal role in activation of multiple inflammatory molecules, and therefore represents the logical target for intervention. We evaluated the feasibility of suppressing the inflammatory responses in different cell lines through specific inhibition of NF-κB by gene transfer of IκBα, the naturally occurring intracellular inhibitor of NF-κB. The IκBα overexpressing cells were established using retroviral gene transfer or stable transfection with the wild-type (wt) IκBα cDNA. In all cell types, overexpression of wt IκBα resulted in a profound (> 100-fold) increase of the IκBα message and a moderate (two-to three-fold) increase of the IκBα protein. The effects of the IκBα overexpression on the NF-κB activation and the inflammatory responses varied significantly in different cell lines. In conditionally immortalized human endometrial stromal cells, overexpression of IκBα prevented both interleukin-1 (IL-1)-inducible degradation of endogenous IκBα protein and activation of NF-κB. Accordingly, induction of cytokines interleukin-8 (IL-8) and Groγ was markedly suppressed. In monocytic THP-1 cells, both lipopolysaccharide (LPS)-inducible degradation of IκBα and NF-κB activation were only partially inhibited by overexpression of exogenous IκBα cDNA. None the less, the LPS-induced transcription of IL-1β and secretion of cytokines interleukin-6 (IL-6) and IL-8 were virtually abolished. In epithelial HT-29 cells, no inflammatory responses were inhibited. These results demonstrate the range of responses in various cell lines to gene transfer of IκBα and indicate the feasibility of suppression of inflammatory responses in appropriate target cells and their progeny by suppression of NF-κB.