Impaired IκB degradation in T cells derived from a subset of RCC patients. Western blotting for IκB was performed on cytoplasmic extract from patient T cells (n = 5). The levels of IκB in the remaining 2 patients (RH and LS) were determined by immunoprecipitating RelA and immunoblotting for IκB (data from RH presented in Fig 3). T cells from 5 different healthy donors served as positive controls. Densitometry analysis of IκB in T cells from normals showed a 73.4% (±6.7% SEM) and 68.5% (±11.3% SEM) decrease after 30 minutes and 2 hours of stimulation, respectively. In patient T cells, IκB levels decreased 10.1% (±4.9% SEM) after 30 minutes and 18.8% (±6.3% SEM) after 2 hours. The data presented here also showed that, within 15 to 30 minutes of stimulation, the phosphorylated form of IκB (P-IκB) was detected in normal T cells but not in patient T cells. In 1 normal, the phosphorylated form of IκB was not detected because of the rapid and total degradation of the inhibitor in 15 minutes.