The phosphorylation of c-Jun NH (2)-terminal protein kinase (JNK), one of the mitogen-activated protein kinases, was analyzed in the sciatic nerves of Lewis rats with experimental autoimmune neuritis (EAN).Western blot analysis showed that the expression levels of both phosphorylated JNK1 (p-JNK1, approximately 46 kDa)and phosphorylated JNK2 (p-JNK2, approximately 54 kDa)in the sciatic nerves of rats with EAN increased significantly (p <0.05)at day 14 post-immunization (PI)and remained at this level at days 24 and 30 PI, with a slight decrease.In EAN- affected sciatic nerves, there was intense immunostaining for p-JNK in the infiltrating inflammatory cells (especially ED1- positive macrophages)and Schwann cells on days 14-24 PI, compared with those of controls.Some macrophages with increased p-JNK immunoreactivity was shown to be apoptotic, while some Schwann cells remained survived in this rat EAN model, suggesting that JNK is differentially involved in the EAN-affected sciatic nerves.These findings suggest that JNK phosphorylation is closely associated with the clearance of inflammatory cells as well as the activation of Schwann cells in the EAN affected sciatic nerves.