Figure 9. Schematic representation of the pathogenic mechanisms of anti–paranodal protein autoantibodies.

(A) Representation of a mature node of Ranvier and myelinated axon. Myelin (yellow) covers the axon except at the node of Ranvier (red). At paranodal junctions (green), Nfasc155 interacts with its axonal partners CASPR1/CNTN1. Nfasc155 is also found at Schmidt-Lanterman incisures (dashed green lines). The Schwann cell nucleus is shown in gray. (B) In neonatal animals, the progressive enwrapping of axons by Schwann cells induces the formation of paranodal regions at node borders. The injection of anti-Nfasc155 IgG4 (blue) during the neonatal period does not affect myelination or node/paranode formation, but induces the depletion of Nfasc155, and thereby alters the formation of paranodal septate-like junctions. (C) At adult age, evidence suggests that the Nfasc155/CASPR1/CNTN1 complex is constantly renewed at paranodes possibly through degradation and replenishment mechanisms. The chronic infusion of anti-Nfasc155 IgG4 (blue) may preclude the regeneration of the paranodal axoglial junction by inducing Nfasc155 depletion, and thereby alter paranode structure and conduction.