Demyelination In Experimental Allergic Neuritis Research Articles

Membrane attack complex of complement is not essential for immune mediated demyelination in experimental autoimmune neuritis

Antibody deposition and complement activation, especially membrane attack complex (MAC) formation are considered central for immune mediated demyelination. To examine the role of MAC in immune mediated demyelination, we studied experimental allergic neuritis (EAN) in Lewis rats deficient in complement component 6 (C6) that cannot form MAC. A C6 deficient Lewis (Lewis/C6−) strain of rats was bred by backcrossing the defective C6 gene, from PVG/C6− rats, onto the Lewis background. Lewis/C6− rats had the same C6 gene deletion as PVG/C6− rats and their sera did not support immune mediated haemolysis unless C6 was added. Active EAN was induced in Lewis and Lewis/C6− rats by immunization with bovine peripheral nerve myelin in complete Freund's adjuvant (CFA), and Lewis/C6− rats had delayed clinical EAN compared to the Lewis rats. Peripheral nerve demyelination in Lewis/C6− was also delayed but was similar in extent at the peak of disease. Compared to Lewis, Lewis/C6− nerves had no MAC deposition, reduced macrophage infiltrate and IL-17A, but similar T cell infiltrate and Th1 cytokine mRNA expression. ICAM-1 and P-selectin mRNA expression and immunostaining on vascular endothelium were delayed in Lewis C6− compared to Lewis rats' nerves. This study found that MAC was not required for immune mediated demyelination; but that MAC enhanced early symptoms and early demyelination in EAN, either by direct lysis or by sub-lytic induction of vascular endothelial expression of ICAM-1 and P-selectin.

Disruption of neurofascin and gliomedin at nodes of Ranvier precedes demyelination in experimental allergic neuritis

High densities of voltage-gated sodium (Nav) channels at nodes of Ranvier enable the rapid regeneration and propagation of the action potentials along myelinated axons. In demyelinating pathologies, myelin alterations lead to conduction slowing and even to conduction block. In order to unravel the mechanisms of conduction failure in inflammatory demyelinating diseases, we have examined two models of Guillain-Barré syndrome: the experimental allergic neuritis induced in the Lewis rat by immunization against peripheral myelin (EAN-PM) and against a neuritogenic P2 peptide (EAN-P2). We found that Nav channel clusters were disrupted at EAN-PM nodes. Neurofascin and gliomedin, two cell adhesion molecules involved with aggregating Nav channels at nodes, were selectively affected prior to demyelination in EAN-PM, indicating that degradation of the axo-glial unit initiated node alteration. This was associated with autoantibodies to neurofascin and gliomedin. Node disruption was, however, independent from complement deposition at nodes, and deposits of the terminal complement complex (C5b-9) were found on the external surface of Schwann cells in EAN-PM. In these animals, the paranodal junctions were also affected and Kv1 channels, which are normally juxtaparanodal, were found dispersed at nodes and paranodes. Altogether, these alterations were associated with conduction deficits in EAN-PM ventral spinal roots. EAN-P2 animals also exhibited inflammatory demyelination, but did not show alteration in nodal clusters or autoantibodies. Our results highlighted the complex mechanisms underlying conduction abnormalities in demyelinating disorders, and unraveled neurofascin and gliomedin as two novel immune targets in experimental allergic neuritis.

647: CD4 + CD25 + T cells prevent induction of demyelination in experimental allergic neuritis (EAN)

Immune tolerance is induced and maintained by T cells, which express CD4 and CD25s the IlI-2 receptor alpha chain. We examine the role of these cells in Lewis rats that had recovered from EAN and were resistant to further disease induction. The CD4+CD25+ and CD4+CD25- T cell subsets were prepared form Lewis rats that had recovered from EAN and from normal Lewis rats and their function compared. First we transferred 5x106 CD4+CD25+ T cells on the day of immunization with bovine peripheral nerve myelin (n=12), these cells suppressed severity of disease to peak at a mean score of 1, compared to controls (n=10) peaking at 2.5 and those given 5×106 CD4+CD25– T cells which peaked at 3 (n=5).

The role of macrophages in demyelination in experimental allergic neuritis

The role of macrophages and serum factors in demyelination in experimental allergic neuritis (EAN) was examined by a simple in vitro method. Cultivated rabbit peritoneal macrophages, preincubated with serum obtained from rabbit EAN produced by sensitization with bovine spinal nerve roots, could agglutinate and phagocytize purified bovine or rabbit peripheral nerve myelin. Sera from normal animals or from controls given adjuvant alone could not. Adhesion and phagocytosis were inhibited if EAN sera were absorbed with peripheral nerve myelin. Rabbit red blood cells were not phagocytized by macrophages exposed to EAN serum. Concomitant to these observations, three lyosomal acid hydrolases: acid proteinase, acid phosphatase and β-glucuronidase, were assayed with respect to their topographical and chronological distribution. In the group examined at clinical onset, increases in the specific activities were 1.5–3.0-fold in the spinal roots and 1.0–1.5-fold in the sciatic nerves compared with control. The degree of increase in total activities per whole root or sciatic nerve was much higher than for specific activities. The topographical distribution of the increase closely corresponded to the histological distribution of EAN lesions. These observations suggested that the increased lysosomal activity originated from lysosomal-rich infiltrating cells. These observations strongly indicated the significant role of macrophages activated by EAN serum in the demyelination of EAN.

Pathogenesis of early phase experimental allergic neuritis: daily monitoring of humoral and cellular immune response to peripheral nerve antigen.

The role of humoral factors in the mechanism of demyelination has been the object of continuous interest. In the present study the role of the antibodies against a peripheral nerve antigenic protein fraction (PN-APF) was studied in the pathogenesis of experimental allergic neuritis (EAN). Blood samples were taken daily starting on the third day after the inoculation of the rabbits and control animals. The titers of anti-PN-APF antibodies were determined by the ELISA method from each sample. The stimulation response of the lymphocytes in a whole blood microculture to the same antigenic protein was also studied and the results are correlated to each other and to the severity of the clinical signs of the disease. At the time of the manifestation of the disease all of the 11 rabbits had measurable levels of antibodies against PN-APF. The stimulation response of the lymphocytes declined at the same time. However, the level of antibody titers and the rate of lymphocyte stimulation response during observation showed no correlation with the severity of the clinical signs. On the basis of the results obtained it seems probable that the antibodies against myelin antigens and lymphocyte stimulation constitute only two of the factors involved in demyelination in EAN.

An untrastructural analysis of remyelination following segmental demyelination.

Electron microscopic observations were made of early remyelination after segmental demyelination in experimental allergic neuritis (EAN) and experimental diphtheritic neuropathy. In EAN 71% of axons which had been demyelinated were invaginated each within a single Schwann cell; remyelination associated with this cellular relationship was in accordance with the spiral myelin concept, 29% of demyelinated axons in EAN were initially enveloped each by several Schwann cell processes and the associated mechanism of remyelination was by “tunication” resulting in a transient irregular distribution of myelin lamellae around the axon circumference. In diphtheritic neuropathy regeneration more closely paralleled development in ontogeny. 88% of demyelinated axons were invaginated each within one Schwann cell, only 12% of axons were each enveloped by more than one Schwann cell process. Early remyelination by tunication was not observed in diphtheritic neuropathy. Additional loosely associated Schwann cell processes lying within the “old” Schwann cell basement membrane occurred frequently in both experimental conditions. Schmidt-Lanterman clefts, “redundant” myelin, and “desmosomes” were observed in the sheaths of incipient remyelination.

The vulnerability of immature rabbits to experimental allergic neuritis: A light and electron microscope study

The vulnerability of immature rabbits to experimental allergic neuritis (EAN) was investigated. The incidence, severity and duration of EAN signs are described; histological changes occuring in dorsal roots and peroneal nervws were observed by light and electron microscopy. Unequivocal signs of EAN occured only in rabbits older than 4 weeks at the time of antigen challenge. Immature EAN rabbits differ in the course of the disease from adults in (a) lower incidence, (b) a greater recovery rate. The time of onset of signs and the duration of signs were not significantly different from the adult group. The results are interpreted in terms of the development of immunological competence, and relative rates of myelic synthesis and myelin degradation. As in the adult, EAN in immature rabbits is characteristically a segmental demyelinating, axon-sparing condition. Demyelination is largely mediated by cells of exogenous origin, though evidence for a contribution by circulating antibodies and degradation of myelin by the Schwann cell is discussed. The type of demyelination represented by EAN is contrasted with that occuring after diptheritic intoxication. The vulnerability of spinal roots to demyelination in EAN is interpreted in terms of the greater permeability of neural capillaries in roots compared with peripheral nerves. The functional significance of the splitting of myelin at the intraperiod line is considered to be related to the putative distribution of encephalitogenic basic protein. A hypothesis is proposed to account for the sparing of the Schwann cell plasma membrane in an autoimmune response which selectively degrades myelin.