An in vitro micromethod for the quantitative assessment of central demyelination

Phagocytosis of myelin by astrocytes in explants of adult rabbit cerebral white matter maintained on Gelfoam matrix

The role of astrocytes in the process of demyelination has been controversial. A culture system in which explants of adult cerebral rabbit white matter were maintained on a Gelfoam matrix was used for evaluating the phagocytosis of myelin by astrocytes without an influx of phagocytic cells derived from actively circulating blood-borne cells. Adult neurons were not viable for more than a few days in these explant cultures, thus resulting in empty myelin sheaths following loss of their axons. After 7 days in vitro, astrocytes, recognized by positivity for glial fibrillary acidic protein by electron microscopic immunocytochemistry, contained numerous membrane-bound vesicles filled with myelin in various stages of degradation. Although the majority of macrophage-like cells were negative for glial fibrillary acidic protein, a minority were positive, in spite of the lack of bundles of intermediate filaments, and were interpreted as astrocytic. Astrocytes were also often positive for glutamine synthetase. This study presents evidence suggesting that astrocytes may actively participate in the phagocytosis and degradation of myelin, a function generally attributed to reactive macrophages.

Theiler's virus replication in brain macrophages cultured in vitro

Infection of the mouse with Theiler's virus is one of the best animal models for the study of multiple sclerosis, a chronic demyelinating disease of the human central nervous system. The identification of the virus target cell(s) is fundamental to an understanding of the viral persistence as well as the inflammation and demyelination observed in the chronic phase of the disease. This paper reports that a small fraction of brain macrophages grown in vitro can be efficiently infected with Theiler's virus without significant cytolytic effect. Viral replication as well as continuous production of infectivity were observed in these cultures.

Suppression of demyelination by mitoxantrone

The mode of action of the immunosuppressant mitoxantrone was examined in murine models of demyelinating disease. The drug has been shown to block antigen induced proliferative activity and to inhibit myelin degradation by leucocytes from paralysed mice. Mitoxantrone blocked myelin breakdown by macrophages although phagocytosis was not affected. Further evidence was obtained to indicate that mitoxantrone acts therapeutically in reducing, or at high dose, preventing signs of EAE developing in mice immunized with spinal cord homogenate and Freund's complete adjuvant. Mitoxantrone also significantly inhibited the incidence of relapse when treatment was initiated during the post-acute remission period.

Degradation of human myelin in vitro by leucocytes from patients with multiple sclerosis

In order to study the possible autoimmune basis of multiple sclerosis (MS) a quantitative method has been used to investigate breakdown of human myelin in vitro. We found that serum from MS patients and controls was generally devoid of any myelin degradative activity. However, isolated peripheral blood mononuclear cells from 43% of MS patients showed significant myelin degradative activity as did those from 61.5% of patients with rheumatoid arthritis (RA). Myelin degradation by cells was found in only 13% of patients with other neurological diseases and in no healthy controls. It is proposed that this non-specific peripheral cellular immune degradative activity originates from cells activated within the central nervous system of MS patients or the joints of individuals with RA. As a result, activity in the blood only indirectly reflects the ongoing inflammatory response at the primary site, accounting for the lack of correlation between changes in the blood and the clinical status of the MS patient. We further propose that the lack of in vitro myelin degradative activity in cells recovered from the cerebrospinal fluid is due to autoaggressive cells being sequestered to the brain.

MS: a localized immune disease of the central nervous system

The precise role of T cells in multiple sclerosis (MS) remains to be defined. No MS-specific antigen has been found. The autoimmune hypothesis for MS rests on immune changes seen in the spinal fluid and brain and on the demonstration, in an experimental animal model, that T cells raised to myelin basic protein transfer demyelination. In this review, Virginia Calder and colleagues focus on recent studies suggesting that in MS, the initial T-cell response occurs within the central nervous system and that the blood poorly reflects this immune activity. This contrasts with the animal model, experimental allergic encephalomyelitis, where the initial immune response is peripheral.

Nervous and immune system disorders in multiple sclerosis

Multiple sclerosis is probably an acquired infectious disease with an autoimmune response relating to damage to the white matter of the central nervous system. There is evidence of continued intrathecal synthesis of oligoclonal antibody and there are perivascular inflammatory cell infiltrates close to areas of demyelination in the central nervous system. Following adoptive transfer, cells sensitized to the myelin basic protein can cause demyelinating disease in rodent recipients. Unlike the peripherally-mediated immune changes in the experimental model it is argued that autoaggressive cells are generated within the CNS in multiple sclerosis. The possible mechanism of cellular demyelination is discussed and the implication for therapy is reviewed.