The node of Ranvier in experimental allergic neuritis: an electron microscope study

Pathological breakdown of the node of Ranvier in experimental allergic neuritis (EAN) in the rabbit was examined by electron microscopy. The study was concerned principally with the mechanism of disruption of paranodal myelin. Two types of change in myelin structure were observed, both apparently related to the presence of cytoplasmic processes of macrophages: (1) a vesicular disorganization of myelin lamellae and (2) a separation of myelin lamellae. Both methods of disorganization were used by macrophages as they apparently lifted off the myelin terminal loops of the paranode from the underlying axon and also penetrated between myelin loops and adjoining myelin lamellae. In some pathologically damaged nodes of Ranvier no macrophages were observed. The findings raise important immunological and electrophysiological questions concerning the involvement of the macrophage in the autoimmune response and the effect of the loss of paranodal myelin on nerve conduction.