Inhibition of COX-2 prevents IVIg-mediated Treg expansion and protection in vivo in EAE model. EAE was induced in 10-week-old female C57BL/6J mice in 3 different groups. The first group received DMSO (solvent control for NS-398) on every alternative day until peak of the disease (day 16). The second group received IVIg (16 mg/mouse) every day and DMSO on every alternative day until day 16. The third group received IVIg every day and NS-398 (100 μg/mouse) on every alternative day until peak of the disease. (A) Mice were sacrificed on the day of onset of clinical signs (day 12) and splenic Tregs (CD4⁺CD25⁺FoxP3⁺) were analyzed by flow cytometry, ***P < .001. (B) Repercussion of COX-2 inhibition in vivo on IVIg-mediated protection from EAE. The development of clinical signs in all the 3 groups of mice was followed until day 28 following induction of EAE, *P < .05; ***P < .001.