Antibody to myelin constituents: a possible factor in induction of cell-mediated demyelination

Effects of the immunomodulator linomide on macrophage migration and myelin phagocytic activity in peripheral nerve trauma: an experimental study

Wallerian degeneration after peripheral nerve transection leads to the phagocytosis of degenerated myelin and axon components by macrophages. These phagocytes are recruited from the systemic circulation and Wallerian degeneration may therefore be used as a model for myelin removal by hematogenous macrophages, a feature that is also a hallmark of demyelinating diseases of the central and peripheral nervous system. The immunomodulator linomide has been shown to be effective in the treatment of experimental demyelinating diseases although the exact mode of its action is not yet defined. The present study investigated the effect of linomide on monocyte invasion and myelin phagocytosis after sciatic nerve transection. Linomide had a dual effect in Wallerian degeneration. Monocyte migration from the circulation to the damaged nervous system was significantly reduced. Additionally, the myelin phagocytic capacity of macrophages was impaired, finally resulting in a significant delay in the removal of myelin. The present experiments may provide an explanation for the effects of linomide during the course of demyelinating diseases of the nervous system.

Astrocytes modulate macrophage phagocytosis of myelin in vitro

Previous work from this laboratory has shown that both macrophages and microglia phagocytize relatively little myelin in vitro under basal conditions. In an effort to better simulate the conditions within the central nervous system (CNS), we have co-cultured these cells with astrocytes, the most numerous of the neural cells in the CNS, and have compared myelin phagocytosis in the co-cultures with that in cells cultured alone. Both macrophages and microglia in company with astrocytes phagocytized about three times as much myelin as controls, as measured by the formation of cholesterol ester, while astrocytes alone showed little evidence of myelin phagocytosis. Astrocyte-conditioned medium increased phagocytic activity in macrophages by 2.3-fold, and by 3.5-fold in microglia. A number of adhesion molecules and extracellular matrices were tested for their effects on myelin phagocytosis. Matrigel was most effective in activating the macrophages, and in the presence of conditioned medium, stimulated these cells to phagocytize as much myelin as when co-cultured with astrocytes. On the other hand, Matrigel inhibited myelin phagocytosis in microglia. These results indicate that activation of macrophages by astrocytes may be due to an adhesion component, as well as to soluble factors secreted by the astrocytes. While microglia were also stimulated by conditioned medium, adhesion to astrocytes or Matrigel induced a downregulation in phagocytic activity.

Activation of adult human derived microglia by myelin phagocytosis in vitro

The present study was designed to determine the extent to which cultured glial cells phagocytose normal central nervous system (CNS) myelin and CNS myelin opsonized with serum or purified antibody against myelin basic protein (MBP). Glial cells studied were mixed cultures (consisting of astrocytes, microglia, and oligodendrocytes) and enriched microglia established from adult human brain specimens and enriched astrocytes from fetal human brain. A human monocytic cell line, THP-1, was included as a control. Uptake of 125I-labelled myelin was followed over a 24 hr time period. An assay of oxidative burst (30 min) and cytokine bioassays measuring IL-1, IL-6, and tumor necrosis factor (TNF) production (6-48 hr) were used to investigate short- and long-term activation of phagocytosing cells. Maximum myelin uptake by phagocytosing glial cells occurred within 12-24 hr following myelin incubation. Opsonization of myelin prior to the phagocytosis assay resulted in greater myelin uptake by mixed glial cell cultures, microglia, and THP-1 cells over that of nontreated myelin. The magnitude of myelin phagocytosis by astrocytes was considerably lower than microglia and THP-1, and was not affected by myelin opsonization. Within 30 min of myelin phagocytosis, microglia and THP-1 cells underwent oxidative burst; opsonization of myelin by purified anti-MBP IgG and heat-inactivated serum enhanced the microglial oxidative burst activity. Production of IL-1, TNF, and most markedly IL-6 by microglia was increased following 12-24 hr of myelin ingestion. Our data demonstrate that myelin phagocytosis by adult human-derived microglia occurs in vitro, is augmented when myelin is opsonized, and results in the activation of microglia as assessed by oxidative burst and cytokine production.

EAE cerebrospinal fluid augments in vitro phagocytosis and metabolism of CNS myelin by macrophages

Previous studies from this laboratory have shown that CNS myelin is phagocytized and metabolized by cultured rat macrophages to a much larger extent when myelin is pretreated with serum containing antibodies to myelin constituents than when it is left untreated or pretreated with non-specific serum. In this study the effect of cerebrospinal fluid (CSF) from rabbits with experimental allergic encephalomyelitis (EAE) in promoting myelin phagocytosis was examined. Fourteen rabbits were immunized with purified myelin in Freund's complete adjuvant, seven of which developed clinical EAE symptoms. Serum and CSF were collected from EAE and control rabbits, and the CSF was centrifuged to remove cells. Sera and CSF from these rabbits and from Freund's adjuvant-immunized controls and untreated controls were measured for IgG content by radial diffusion assay, their myelin antibody characteristics were analyzed by immunoblots, and the ability of these serum and CSF samples to promote myelin phagocytosis when used for myelin opsonization was examined. The ability of a CSF sample to enhance radioactive myelin uptake and phagocytosis by cultured macrophages as measured by the appearance of radioactive cholesterol ester was linearly proportional to its total IgG titer, and correlated approximately both with clinical symptoms of the animal and the presence of antibody against the myelin constituents myelin basic protein, proteolipid protein, and galactocerebroside. The cholesterol esterification activities of EAE sera correlated to a lesser extent with IgG levels and clinical symptoms.(ABSTRACT TRUNCATED AT 250 WORDS)

Induction of anti-myelin antibodies in EAE and their possible role in demyelination

Experimental allergic encephalomyelitis is characterized by invasion of lymphocytes and macrophages into the central nervous system resulting in inflammation, edema, and demyelination. Sera from Lewis rats from 7-95 days after immunization with purified guinea pig CNS myelin were examined with respect to their ability to opsonize myelin. This was correlated with the appearance of antibody components and the relative amounts of antibody to myelin basic protein (MBP) and proteolipid protein (PLP). Sera from rats 10-95 days after immunization preincubated with purified myelin induced phagocytosis of myelin by cultured macrophages with the resulting production of cholesterol ester. This opsonization activity as measured by the percentage of cholesterol esterified reached a peak at 26-27 days after immunization but remained significantly elevated up to 95 days post-immunization compared to the activity of serum from the Freund's adjuvant-injected controls. Immunoblots of the sera revealed a gradual increase in antibody activity against myelin components. ELISA assays for MBP and PLP antibody showed a similar pattern. Antibody to galactocerebroside (GC) was not detected by immunostains nor by the ELISA assay. Areas of demyelination were observed histologically by luxol-fast blue stained spinal cords up to 60 days post-immunization. These results indicate that antibodies to myelin protein when given access to myelin through or within the blood brain barrier could initiate or enhance the phagocytic response by peripheral or resident macrophages.

Opsonization of normal myelin by anti-myelin antibodies and normal serum

Fc receptor-dependent myelin phagocytosis has been proposed as a possible important effector mechanism in several immune-mediated demyelinating diseases. The present study was designed to determine whether myelin is opsonizable by anti-myelin antibodies. Thioglycolate-elicited mouse peritoneal macrophages were cultured with 125I-labelled bovine central myelin pretreated with normal or immune serum. Serum opsonic activity was determined by a kinetic study comparing macrophage uptake of opsonized and untreated 125I-myelin. Heat-stable and heat-labile myelin opsonins were detected in normal rabbit serum. Myelin was also opsonized by normal rabbit gamma globulin and by heat-inactivated normal mouse, human, and guinea pig serum. Increased opsonic activity was detected in rabbit anti-myelin antiserum and the gamma globulin fraction prepared from this serum, in anti-myelin basic protein and anti-galactocerebroside antiserum but not in anti-myelin-associated glycoprotein antiserum or in serum from rabbits injected with Freund's adjuvant alone. One out of three anti-sheep red blood cell antisera tested also showed increased myelin opsonic activity. It is concluded that anti-myelin antibodies can promote opsonic phagocytosis, and that normal serum and normal serum gamma globulin also opsonize myelin.

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.

An in vitro micromethod for the quantitative assessment of central demyelination

We report the development of a simple and reliable method for the study of demyelination in vitro based on the measurement of 2':3'-cyclic nucleotide 3'-phosphodiesterase in isolated myelin. Using only small quantities of myelin (equivalent to 100 micrograms of myelin protein) the system was tested under conditions that are believed to approximate those found at the site of an inflammatory demyelinating lesion. Treatment with a combination of trypsin, phospholipase A2, and lysophosphatidylcholine was used to evaluate the method. This microsystem has the potential not only for testing the myelinotoxicity of soluble factors but also for investigating the involvement of inflammatory cells in the demyelinating process. Myelin degradation by elicited peritoneal macrophages could be demonstrated at relatively high densities of these cells. Nylon wool purified lymph node T cells from myelin basic protein-primed SJL/J mice, after selective expansion with antigen and interleukin 2, failed to induce any significant myelin breakdown unless a limited number of syngeneic activated macrophages were also present. T cells from mice that had been inoculated with keyhole limpet haemocyanin failed to show any effect. The advantages of this technique over other in vitro systems are that it enables the study of demyelination using syngeneic sources of myelin and defined cell populations.