(a–d) Effect of anti-CD3 mAb on Na⁺/K⁺-ATPase activity. Mice were injected with control or anti-CD3 mAb and enzyme activity measured in jejunum isolated 3 hours later. Values are means ± SE for four to six determinations in each group. Results in unstimulated mice treated with anti-TNF (a) or anti–IFN-γ (b) mAbs were not different from control mAb-treated, unstimulated mice (data not shown). In (a) and (b), results in control mAb-treated, anti–CD3-stimulated mice were compared with unstimulated mice. Results of anti–cytokine-treated, anti–CD3-stimulated mice were compared with control mAb-treated, anti–CD3-stimulated mice. In (c), data in B6, anti–CD3-stimulated mice were compared with B6, unstimulated mice and results in anti-CD3-stimulated, TNFR-1^–/– and IFN-γ^–/– mice were compared with B6, anti–CD3-stimulated mice. In (d), results in anti-CD3 mAb-stimulated, TNF-treated and IFN-γ–treated mice were compared with control mAb-treated mice. (e) Effect of anti-CD3 mAb on abundance of Na⁺/K⁺-ATPase α and β subunits. Microsomal membranes were isolated and analyzed on SDS-PAGE, and Western blots were performed using mAb to the α and β subunits. *P < 0.05, **P < 0.01 compared with control by ANOVA.