The relationship between human multiple sclerosis and rodent experimental allergic encephalomyelitis

The pathobiology of myelin mutants reveal novel biological functions of the MBP and PLP genes

Substantial biological data indicate that the myelin basic protein (MBP) and myelin proteolipid protein (PLP/DM20) genes produce products with functions beyond that of serving as myelin structural proteins. Much of this evidence comes from studies on naturally-occurring and man-made mutations of these genes in mice and other species. This review focuses upon recent evidence showing the existence of other products of these genes that may account for some of these other functions, and recent studies providing evidence for alternative biological functions of PLP/DM20. The MBP and PLP/DM20 genes each encode the classic MBP and PLP isoforms, as well as a second family of proteins that are not involved in myelin structure. The biological roles of these other products of the genes are becoming clarified. The non-classic MBP gene products appear to be components of transcriptional complexes in the nucleus, and they also may be involved in signaling pathways in T-cells and in neural cells. The non-classic PLP/DM20 gene products appear to be components of intracellular transport vesicles in oligodendrocytes. There is evidence for other functions of the classic PLP/DM20 proteins, including a role in neural cell death mechanisms, autocrine and paracrine regulation of oligodendrocytes and neurons, intracellular transport and oligodendrocyte migration.

Mast cells: new targets for multiple sclerosis therapy?

Growing evidence suggests that mast cells (MCs) play a crucial role in the inflammatory process and the subsequent demyelination observed in patients suffering from multiple sclerosis (MS). Although no consensus exists on the role of mast cells in multiple sclerosis, recent results from animal models clearly indicate that these cells act at multiple levels to influence both the induction and the severity of disease. In addition to changing our views on the pathophysiology of multiple sclerosis, the concept that mast cells are critical for the outcome of the disease could have an important impact on the development of new therapeutic approaches.

Intranasal peptide-induced peripheral tolerance: the role of IL-10 in regulatory T cell function within the context of experimental autoimmune encephalomyelitis

Experimental autoimmune encephalomyelitis (EAE) is a T cell-mediated autoimmune disease commonly employed as a model for multiple sclerosis. Extensive studies have demonstrated that EAE may be prevented or ameliorated by the intranasal administration of soluble peptides representing encephalitogenic epitopes. There is increasing evidence that this peptide administration may function via the generation of regulatory cells. The mechanism of action of these cells remains controversial and it seems likely that it may vary between experimental models. At present the majority of work on regulatory cells has centred on characterising naturally occurring regulators, or those generated artificially ex vivo, and less is known about induced regulatory cells produced following peptide administration. This report aims to briefly outline the evidence for the existence of natural regulatory T cells and to introduce the sub-types of induced regulatory T cells now recognised. In several of these regulatory cell systems investigated to date, interleukin-10 (IL-10) has been shown to be important in cell function. This has not been directly investigated in a model employing peptide therapy to induce peripheral tolerance, hence the purpose of this study was to investigate the role of IL-10 in the generation of these regulatory cells. This work has employed both a TCR transgenic mouse system, for predominantly in vitro studies of cell function, and an IL-10 knock-out mouse strain to investigate in vivo disease protection. The results summarised in this report demonstrate that IL-10 is fundamentally important in the generation of disease protection following intranasal peptide therapy.

Distinct roles for matrix metalloproteinase-2 and alpha4 integrin in autoimmune T cell extravasation and residency in brain parenchyma during experimental autoimmune encephalomyelitis

Expression of alpha4 integrin by auto-reactive T cells is critical for their ability to induce EAE, an autoimmune disease of the central nervous system in mice, used as a model to study human multiple sclerosis. Having previously identified one role for alpha4 integrin in adhesion-mediated induction of matrix metalloproteinase-2 (MMP-2), an enzyme that degrades the subendothelial basement membrane matrix, we investigated independent roles for MMP-2 and alpha4 integrin during EAE. The data suggest that expression of alpha4 integrin by auto-reactive T cells is important not only in mediating MMP-2 induction to facilitate entry into the CNS, but also plays a role in maintaining residency within the CNS.

Hydroxyzine inhibits experimental allergic encephalomyelitis (EAE) and associated brain mast cell activation

Experimental allergic encephalomyelitis (EAE) has been used as an animal model for the human demyelinating disease multiple sclerosis (MS). In acute MS or EAE, early disruption in the integrity of the blood-brain-barrier (BBB) precedes brain infiltration by inflammatory cells or any clinical evidence of disease. BBB permeability could be affected by vasoactive mediators and cytokines released from perivascular brain mast cells. We investigated the number and degree of activation of brain mast cells in EAE and the effect of the heterocyclic histamine-1 receptor antagonist hydroxyzine, a piperazine compound known to also block mast cells. Acute EAE was induced in Lewis rats by immunization with whole guinea pig spinal cord homogenate and complete Freund's adjuvant (CFA). A second group of animals were treated orally with hydroxyzine for one day before immunization and then continuously for 14 days. Control rats were treated with CFA or hydroxyzine alone. The clinical progression of EAE was assessed on days 10, 12 and 14 after immunization. The number of metachromatic mast cells and the degree of degranulation was assessed in the thalamus with light microscopy. At day 14, there was a three-fold increase in the number of brain mast cells with EAE, as compared to controls. These cells were positive for the immunoglobulin E binding protein (FcepsilonRI), while those from control rats were not. Over 40% of all thalamic mast cells studied in EAE showed partial staining or extruded secretory granule indicative of secretion. Hydroxyzine treatment inhibited (p<0.05) the progression and severity of EAE by 50% and the extent of mast cell degranulation by 70% (p<0.05). These findings indicate that brain mast cells are associated with EAE development and that inhibition of their activation correlates positively with the clinical outcome.

Golli-Induced Paralysis: A Study in Anergy and Disease

The Golli-MBP transcription unit contains three Golli-specific exons as well as the seven exons of the classical myelin basic protein (MBP) gene and encodes alternatively spliced proteins that share amino acid sequence with MBP. Unlike MBP, which is a late Ag expressed only in the nervous system, Golli exon-containing gene products are expressed both pre- and postnatally at many sites, including lymphoid tissue, as well as in the central nervous system. To investigate whether Golli-MBP peptides unique to Golli would result in neurological disease, we immunized rats and observed a novel neurological disease characterized by mild paralysis and the presence of groups of lymphocytes in the subarachnoid space but not in the parenchyma of the brain. Disease was induced by Th1-type T cells that displayed an unusual activation phenotype. Primary stimulation in vitro induced T cell proliferation with increased surface CD45RC that did not become down-regulated as it did in other Ag-stimulated cultures. Secondary stimulation of this CD45RChigh population with Ag, however, did not induce proliferation or IL-2 production, although an IFN-γ-producing population resulted. Proliferation could be induced by secondary stimulation with IL-2 or PMA-ionomycin, suggesting an anergic T cell population. Cells could adoptively transfer disease after secondary stimulation with IL-2, but not with Ag alone. These responses are suggestive of a chronically stimulated, anergic population that can be transiently activated to cause disease, fall back into an anergic state, and reactivated to cause disease again. Such a scenario may be important in chronic human disease.

Increased calpain expression in activated glial and inflammatory cells in experimental allergic encephalomyelitis

In demyelinating diseases such as multiple sclerosis (MS), myelin membrane structure is destabilized as myelin proteins are lost. Calcium-activated neutral proteinase (calpain) is believed to participate in myelin protein degradation because known calpain substrates [myelin basic protein (MBP); myelin-associated glycoprotein] are degraded in this disease. In exploring the role of calpain in demyelinating diseases, we examined calpain expression in Lewis rats with acute experimental allergic encephalomyelitis (EAE), an animal model for MS. Using double-immunofluorescence labeling to identify cells expressing calpain, we labeled rat spinal cord sections for calpain with a polyclonal millicalpain antibody and with mAbs for glial (GFAP, OX42, GalC) and inflammatory (CD2, ED2, interferon gamma) cell-specific markers. Calpain expression was increased in activated microglia (OX42) and infiltrating macrophages (ED2) compared with controls. Oligodendrocytes (galactocerebroside) and astrocytes (GFAP) had constitutive calpain expression in normal spinal cords whereas reactive astrocytes in spinal cords from animals with EAE exhibited markedly increased calpain levels compared with astrocytes in adjuvant controls. Oligodendrocytes in spinal cords from rats with EAE expressed increased calpain levels in some areas, but overall the increases in calpain expression were small. Most T cells in grade 4 EAE expressed low levels of calpain, but interferon gamma-positive cells demonstrated markedly increased calpain expression. These findings suggest that increased levels of calpain in activated glial and inflammatory cells in EAE may contribute to myelin destruction in demyelinating diseases such as MS.

Acquired resistance to experimental autoimmune encephalomyelitis is independent of V beta usage

In Lewis rats, activated encephalitogenic T-helper cells elicit a single bout of experimental autoimmune encephalomyelitis (EAE). Recovery from EAE is marked by reduced susceptibility to disease reinduction. The purpose of this study was to determine whether a dominant expression of V beta gene segments by encephalitogenic T cells was required for development of recovery-associated resistance. Several polyclonal and monoclonal T cell lines were derived from Lewis rats sensitized with R72-86, a synthetic peptide representing the 72- to 86-amino-acid sequence of rat myelin basic protein (RMBP). The results revealed broad heterogeneity among encephalitogenic T cells specific for R72-86 in regard to V beta expression and CDR3 sequence. Encephalitogenic clones exclusively bearing either V beta 4 or V beta 10 TCR or polyclonal T cells bearing heterogeneous TCR transferred EAE to recipient rats and elicited resistance to EAE as revealed by subsequent challenge with guinea pig (GP)MBP in complete Freund's adjuvant (CFA). Nonpathogenic V beta 3+ and V beta 8.6+ clones specific for the 68-86 and 55-66 regions of MBP, respectively, did not elicit effective protection from EAE. These data indicate that induction of postrecovery resistance to EAE does not depend upon a particular V beta usage.