Acquired Neuropathies Figure 5. Comparison of paranodin immunoreactivity in several patients with CIDP and CIAP. Longitudinal sections from superficial peroneal nerves were immunostained with antibodies for paranodin in four patients with CIDP (A) and four patients with CIAP (B). The patient numbers are indicated on the figure. In CIDP samples paranodin immunoreactivity was visible along the internode in most fibers (A, arrows). In contrast in CIAP paranodin was restricted to the nodes (B, arrows), which appeared often asymmetrical or irregular. Scale bar 20 mm. doi:10.1371/journal.pone.0014533.g005 ture of nodes of Ranvier on longitudinal sections. Electron microscopy demonstrated the existence of alterations of nodal and paranodal regions in both CIDP and CIAP. As expected, alterations predominated in Schwann cells in CIDP, and in axons in CIAP. We also observed internodes with thin myelin or irregular myelination in CIAP, including heminodes, which were confirmed by counting after immunostaining. This finding is likely to correspond to regenerating fibers on which remyelination was taking place. Immunofluorescence studies of nodal and paranodal proteins showed important alterations that were even more pronounced that what would have been expected from the electron microscopy study. These results suggest that organization of axonal domains is very sensitive to pathological alterations of both axons and Schwann cells. In CIAP, paranodin labeling of paranodes was irregular and interrupted, in relation to the ultrastructural findings showing axonal alterations. The relative nodal concentration of KCNQ2 and Nav channels was preserved, although some Nav immunoreactivity was detected all along the axons. This pattern of Nav channel immunostaining may correspond to the extensive zones of sodium channel staining reported along regenerating axons with ongoing remyelination after crushing the rat peroneal nerve [33]. Similar Figure 6. KCNQ2 immunoreactivity in a control nerve and in patients with CIDP and CIAP. Immunolocalization of KCQN2 (green) and voltage-gated Na+ channels (Nav, red) in longitudinal sections of superficial peroneal nerves. A. KCNQ2 and Nav immunoreactivities colocalize at the nodal region in the control nerve (arrowheads) and are not detected in the internodes. B. In a CIDP nerve (Patient 5), nodal KCNQ2 immunoreactivity is low (asterisk) or absent (arrowhead) and only a few nodes are labeled. A weak immunoreactivity is observed for the two ion channels in some internodes. C. In a CIAP sample (Patient 18), KCNQ2 and Nav colocalization is observed at nodes (arrowheads) but some immunoreactivity is also detected along the fibers. Scale bar: 20 mm. doi:10.1371/journal.pone.0014533.g006 PLoS ONE | www.plosone.org 6 January 2011 | Volume 6 | Issue 1 | e14533