Etiology and pathogenesis of monophasic and relapsing inflammatory demyelination - human and experimental

Characteristics of in vitro cytotoxic effects of myelin basic protein-reactive T cell lines on syngeneic oligodendrocytes

We have previously found that Lewis rat myelin basic protein (MBP)-reactive lymphocytes (Lc) were cytotoxic in vitro to cultured syngeneic oligodendrocytes (oligos). We report here additional studies to characterize this reaction. The effector lymphocytes in the cytotoxic reaction are also encephalitogenic as evidenced by the capacity of other aliquots of these cells to transfer experimental allergic encephalomyelitis (EAE). We confirmed that the presence of both MBP and antigen-presenting cells (APC) are required for this in vitro cytotoxic effect. This reaction (measured by 51Cr release from labeled oligos) is dose-dependent on the effector/target ratio with marked 51Cr release at a 20/l ratio. Effector/target cell contact is required since: (a) 51Cr release is not significantly increased when effector Lc and oligo are separated by a micropore membrane (28% vs. 24% spontaneous release); (b) no cytotoxic activity is present in the supernatant fluid of a toxic reaction. The adhesion of 51Cr-labeled effector Lc to unlabeled oligo is increased in the presence of both MBP and APC (21 +/- 1.0% of cell adhering) as compared with effector Lc + APC (12 +/- 2.7%), or effector Lc alone (14 +/- 2.8%). Surface expression of class I major histocompatibility complex (MHC) antigens was expressed on the surface of the target oligos during this in vitro cytotoxic reaction. This may explain our previously observed MHC restriction in this reaction. The findings described here may explain some of the in vivo pathogenic events in EAE.

Sites of egress of inflammatory cells and horseradish peroxidase transport across the blood-brain barrier in a murine model of chronic relapsing experimental allergic encephalomyelitis

Results are reported of experiments designed to focus at attachment sites of inflammatory cells (ICs) on the luminal surface of brain endothelial cells (ECs) and on the mechanisms of horseradish peroxidase (HRP) transport across the altered blood-brain barrier (BBB) in a murine model of chronic relapsing experimental allergic encephalomyelitis. Cationized ferritin (CF) served as a marker for evaluating the electrostatic nature of brain microblood vessels (MBVs) on the plasma membranes of ICs or normal mouse peripheral white blood cells and erythrocytes. SJL/J mice demonstrating clinical illness were given HRP or CF, in vivo or in situ, respectively. Light microscopy and conventional transmission electron microscopy of cerebellum or thoracic and lumbar spinal cord regions demonstrated HRP leakage most pronounced in MBVs with perivascular infiltrates. HRP traversed across the ECs via numerous vesicles and tubular profiles located mostly in the parajunctional regions, while EC junctions appeared closed. Scanning electron microscopy demonstrated that IC attachment was primarily at parajunctional sites on the EC surface. We also observed increased microvillar projections extending from the EC surface into the lumen. CF demonstrated a patchy decoration on both the luminal EC surface and IC membranes but did not label uncoated invaginating membrane pits or tubular structures. Our data indicate that the points of attachment of the ICs on the EC surface may reflect specific receptor sites where the ICs eventually gain entrance into CNS across the BBB during brain inflammation.

Induction of synchronized relapses in SJL/J mice with chronic relapsing experimental allergic encephalomyelitis

Chronic relapsing experimental allergic encephalomyelitis (CR-EAE) was induced in SJL/J mice by two injections of encephalitogenic emulsion. The majority of mice developed multiple relapses from day 22 to day 367 post injection. To induce synchronized relapses a third injection of the encephalitogenic emulsion was given. Almost all mice that received the third injection developed an acute, synchronized relapse with severe clinical signs within 7 to 11 days. Histologically, there was no difference between the lesions in the spontaneous versus the precipitated relapse. CR-EAE in SJL/J mice modified with the third injection offers an advantage of a reproducible and well-timed acute relapse, which allows precise dissection of the immunological events governing spontaneous relapses in chronic EAE.

Extravasation of polymorphonuclear leukocytes from the cerebral microvasculature. Inflammatory response induced by alpha-bungarotoxin

Postcapillary venules represent the segment of the microvasculature most vulnerable to inflammatory processes. While there is a considerable body of data on the peripheral vasculature, little is known about the primary events occurring during inflammatory reactions in cerebral blood vessels. We introduce here a model by which the migration of polymorphonuclear leukocytes through the CNS endothelial barrier can be studied. Alpha-bungarotoxin is used as a chemotactic agent and is shown, for the first time, to act by activating the complement cascade. Leukocytes migrate through the endothelium transcellularly. Two modes of migration are described: a direct mode whereby the cells use temporary pores in the vessel wall as portals, and an indirect mode whereby the leukocytes leave the vascular compartment after being enveloped by and incorporated into endothelial cells. The functional implications of these findings lead us to conclude that the direct mode of migration is a causal agent in the massive breakdown of the blood-brain barrier under acute inflammatory conditions.

Ultracytochemical distribution of myelin basic protein after injection into the cerebrospinal fluid. Evidence for transport through the blood-brain barrier and binding to the luminal surface of cerebral veins

Distribution of myelin basic protein (MBP) in the central nervous system (CNS) following injection into the cerebrospinal fluid (CSF) was studied by different qualitative and quantitative immunelectron -microscopic techniques. Endogenous MBP was present in myelin sheaths in injected as well as in control animals. After injection of exogenous MBP into CSF this protein was present in the subarachnoid space, on the surface of meningeal cells, on the surface of collagen fibers, in the basement membrane of the glia limitans, in vessel walls, and in the extracellular space of spinal roots. In meningeal veins, endothelial vesicles filled with peroxidase reaction product were found on the abluminal side of endothelial cells, in the endothelial cytoplasm and sometimes opening into the vascularllumen . In addition patchy staining of the luminal surface of endothelial cells was noted, indicating binding of antigen at this location. Quantitative immunelectron microscopy (an indirect technique with rabbit anti-MBP serum as primary layer and gold-labeled anti-rabbit IgG as secondary layer) revealed highly significant MBP binding on the luminal surface of endothelial cells after injection of this antigen into the CSF. The present results indicate that MBP, when liberated in CNS is transported through the blood-brain barrier and presented on the luminal surface of endothelial cells of the cerebral and meningeal veins. This observation may be important in interpretation of pathogenesis of initial inflammatory infiltrates in experimental allergic encephalitis (EAE).