ANTIBODY RESPONSE TO CENTRAL AND PERIPHERAL NERVE ANTIGENS IN RAT AND GUINEA-PIG

CIDP: Current Treatments and Identification of Targets for Future Specific Therapeutic Intervention

Chronic inflammatory demyelinating polyneuropathy (CIDP) is an acquired immune-mediated inflammatory disorder of the peripheral nervous system. This clinically heterogeneous neurological disorder is closely related to Guillain–Barré syndrome and is considered the chronic counterpart of that acute disease. Currently available treatments are mostly empirical; they include corticosteroids, intravenous immunoglobulins, plasma exchange and chronic immunosuppressive agents, either alone or in combination. Recent advances in the understanding of the underlying pathogenic mechanisms in CIDP have brought a number of novel ways of possible intervention for use in CIDP. This review summarizes selected pre-clinical and clinical findings, highlights the importance of using adapted animal models to evaluate the efficacy of novel treatments, and proposes the outlines of future directions to ameliorate the conditions of patients with CIDP.

Attempts to transfer experimental allergic neuritis with lymphocytes

Attempts have been made to transfer experimental allergic neuritis (EAN) both by the intraneural and the intravenous injection of cells derived from Lewis rats with the disease into naive recipients of the same strain. Lymph node cells obtained 12 and 15 days after inoculation with bovine dorsal root in Freund's complete adjuvant were injected intraneurally. A small number of demyelinated axons were observed, but clinical weakness was not evident. Lymph node cells, lymph node cells cultured with concanavalin A, or cultured spleen cells from animals with EAN were transferred intravenously to normal rats. Uncultured lymph node cells were transferred to X-irradiated animals. There were no clinical or histological differences between these recipients and controls receiving cells from rats inoculated with Freund's adjuvant alone. The findings are discussed in relation to previous reports of attempts to transmit EAN by cell transfer.

The effect of suppression of macrophage activity on the development of experimental allergic neuritis

The selective toxicity of silica dust for macrophages has been used to assess the role of these cells in experimental allergic neuritis (EAN). Inbred Lewis rats were inoculated with bovine dorsal roots in Freund's complete adjuvant (day 0). In two experiments, animals received 200 mg of silica dust in 1 cm3 of saline intraperitoneally (IP) at days 8 and 16. In another two experiments, animals received IP silica at days 3, 7, and 11. Control animals received 1 cm3 saline IP at corresponding times. Regular clinical assessment showed that in animals treated on days 8 and 16 there was a significant delay in the time taken to reach their maximum degree of illness. This delay was not seen in the animals treated on days 3, 7, and 11. Neither of the injection regimes reduced the final maximum severity of the disease. In three experiments recovery of the treated and control animals occurred concurrently, hence the duration of the disease was reduced in the animals treated at days 8 and 16. However, in one group of animals given silica at days 3, 7 and 11, there was a delay in the time taken to recover from the most severe phase of the disease but thereafter the treated animals improved more quickly to reach their best grade at the same time as the controls. If the silica blockade of macrophages is to be effective in delaying the onset of EAN, the timing of injections is critical.

The treatment of experimental allergic neuritis by plasma exchange

Experimental allergic neuritis (EAN) is a demyelinating disease of the peripheral nervous system that can be induced in laboratory animals. This disorder has been considered to show many similarities to acute inflammatory polyneuropathy (Guillain-Barré syndrome, GBS). Reports that plasma exchange may benefit patients with GBS prompted the investigation of the effect of plasma exchange in EAN. A controlled study was performed on New Zealand White rabbits. Sixteen animals were allocated to control or treatment groups at the onset of the disease. Clinical assessment on days 7 and 14 showed that treated animals were less severely affected neurologically (P = 0.05, day 7; P less than 0.001 day 14), with a commensurate reduction in the severity of the histological lesions in peripheral nerves.

Suppression of experimental allergic neuritis by Cyclosporin-A

Experimental allergic neuritis (EAN) was induced in guinea pigs and rats and treated with Cyclosporin-A (Cy-A). When Cy-A was given prophylactically for 1 month from the time of induction of the disease, it prevented the development of EAN during the course of its administration. When Cy-A was given therapeutically after the onset of neurological signs, it effectively prevented further deterioration. This effect was more marked after 3 weeks' treatment than after only 1 week's treatment. In both regimens, when dosing with Cy-A ceased there was a latent period before clinical signs of EAN developed. This latent period is similar to that seen in the development of EAN in normal control animals and is probably due to the continued presence of antigen at the injection sites. After primary treatment of EAN with Cy-A, animals that relapsed did not respond to further treatment with Cy-A. Histological examination revealed that the nature of the EAN lesions in both groups of animals given Cy-A were not as severe as those seen in control animals. Despite these observations, there was no statistically significant difference between the maximum clinical grades reached by animals in any one group. These experiments suggest that T-cells are important in the development of EAN and that Cy-A interferes with this process by suppressing T-helper cells. They also show that it is possible to influence favourably the course of immune mediated neurological disease.

Effects of plasmapheresis on the course of experimental allergic neuritis in rabbits

Experimental allergic neuritis was induced in 30 rabbits with extract of bovine peripheral nerve in complete Freund's adjuvant. Of the 22 animals that completed the study, nine animals were plasmapheresed within two weeks of inoculation and 13 animals served as controls. The plasmapheresed animals developed a less severe form of EAN than the controls. Differences were apparent in clinical weakness, weight loss, degree of dispersion of the muscle action potential and histological changes.

Experimental allergic neuritis in the Lewis rat: characterization of the activity of peripheral myelin and its major basic protein,P2

Experimental allergic neuritis has been produced in the inbred Lewis rat in the absence of experimental allergic encephalomyelitis (EAE) using bovine intradural root myelin. The lack of EAE is probably because P1 is only weakly encephalitogenic in the rat. One of the basic proteins of bovine peripheral myelin, P2, was isolated and demonstrated to be pure by amino acid analysis and SDS PAGE. It was found to have a molecular weight of 15,400 and contained 4 mol 1/2-cystine/mol. This P2 was found to be highly neuritogenic and is probably the sole neuritogenic antigen in this system. The successful demonstration of its neuritogenicity must be due in large part to the use of the inbred Lewis rat and bovine P2, but an explanation could also involve the omission of denaturing organic solvents, the prevention of oxidative denaturation and presumably the fact that any changes which may occur are not sufficient to prevent recognition of the active site by the immune system of the inbred Lewis rat. P2 was neuritogenic down to 5 micrograms/animal. Its activity was enhanced by but not dependent on the presence of Mycobacterium in the adjuvant. This suggested that release of P2 could possibly break tolerance and produce an auto-immune disease such as the Guillain--Barre syndrome.

Cellular hypersensitivity to basic myelin (P2) protein in the Guillain-Barré syndrome

Lymphocytes of 29 subjects were assayed for MIF production in response to P2 peripheral nerve protein, crude human peripheral nerve and human central nervous system Al basic myelin protein. Seven were performed in normal control subjects, 12 in Guillain-Barre patients (GB), 5 with other polyneuropathies and 5 in patients with multiple sclerosis (MS). Only GB patients with acute illness produced MIF in response to neuritogenic P2 protein and crude human nerve. Two MS patients in the acute phase of an exacerbation and one GB patient produced MIF in Response to Al protein. The results of this study demonstrate cellular hypersensitivity to a neuritogenic consituent in peripheral nervous tissue and support the concept that this may be important in the pathogenesis of GB.

Demonstration of antimyelin antibodies by immunofluorescence in Guillain-Barré syndrome

IgG, IgA and IgM antibodies reacting with myelin sheaths were found in the sera but not in the cerebrospinal fluid of four out of six patients with Guillain-Barré syndrome. These antibodies had organ specificity for myelin of the central and peripheral nervous systems but did not demonstrate species specificity. Similar antibodies, but in much lower titres, were found infrequently in the sera of patients with liver disease and rarely in normal individuals. The organ specificity and the close correlation between antibody titres and disease activity suggest the possibility that these antibodies may play a role in the pathogenesis of Guillain-Barré syndrome. The detection of antimyelin antibodies by immunofluorescence may provide a relatively simple ancillary laboratory aid in the diagnosis of the neurological entity.