Inhibition of experimental allergic encephalomyelitis with an antibody that recognizes a novel antigen expressed on lymphocytes, endothelial cells, and microglia

Angiogenesis is present in experimental autoimmune encephalomyelitis and pro-angiogenic factors are increased in multiple sclerosis lesions

Background

Angiogenesis is a common finding in chronic inflammatory diseases; however, its role in multiple sclerosis (MS) is unclear. Central nervous system lesions from both MS and experimental autoimmune encephalomyelitis (EAE), the animal model of MS, contain T cells, macrophages and activated glia, which can produce pro-angiogenic factors. Previous EAE studies have demonstrated an increase in blood vessels, but differences between the different phases of disease have not been reported. Therefore we examined angiogenic promoting factors in MS and EAE lesions to determine if there were changes in blood vessel density at different stages of EAE.

Methods

In this series of experiments we used a combination of vascular casting, VEGF ELISA and immunohistochemistry to examine angiogenesis in experimental autoimmune encephalomyelitis (EAE). Using immunohistochemistry we also examined chronic active MS lesions for angiogenic factors.

Results

Vascular casting and histological examination of the spinal cord and brain of rats with EAE demonstrated that the density of patent blood vessels increased in the lumbar spinal cord during the relapse phase of the disease (p < 0.05). We found an increased expression of VEGF by inflammatory cells and a decrease in the recently described angiogenesis inhibitor meteorin. Examination of chronic active human MS tissues demonstrated glial expression of VEGF and glial and blood vessel expression of the pro-angiogenic receptor VEGFR2. There was a decreased expression of VEGFR1 in the lesions compared to normal white matter.

Conclusions

These findings reveal that angiogenesis is intimately involved in the progression of EAE and may have a role in MS.

Pathogenesis of some neurological immune ultrastructural and morphometrical observations on rat thymus

Numerous studies on neuro-immuno-modulation indicate that the thymus is involved in many neurological diseases, including experimental allergic encephalomyelitis (EAE). Twenty Lewis rats were induced for EAE. At X, XII, XX and XXX days post-inoculation the animals were killed, and the thymus was recovered and harvested. Specimens of thymus were submitted to morphological light microscopy analysis (1% toluidine blue) and ultra-structural analysis (transmission electron microscopy). Significant morphometric data were collected by examining the images quantitatively and by statistically analysing the values. Our results show that the microenvironment of the thymus is severally involved in acute EAE. Thymocytes and reticular epithelial cells show many changes which are closely related to the pathogenesis of EAE. In particular we observed: (1) inside the cell an increase in intra-cytoplasmic vacuoles, and changes in the thickness of the nuclear membrane, mitochondria, rough endoplasmic reticulum, cellular inter-digitations and cellular electron-density; (2) outside the cell an increase in pericellular translucent halo, intercellular spaces, intercellular contacts and apoptotic and necrotic figures. The evidence of a thymic role in MS may suggest the intriguing therapeutic concept of thymectomy in the management of this neurological disease.

Antisecretory factor expression is regulated by inflammatory mediators and influences the severity of experimental autoimmune encephalomyelitis

Antisecretory factor (ASF) was originally identified as a potent inhibitor of intestinal fluid secretion induced by a number of enterotoxins. In addition to its involvement in intestinal fluid secretion, ASF modulates the proliferation of memory/effector T cells and is expressed by cells of the immune system. This report describes the role of ASF in modulating immune responses and assesses the regulation of ASF during an in vivo immunological reaction. ASF expression was redistributed during adoptively transferred experimental autoimmune encephalomyelitis (EAE), and in response to other inflammatory stimuli. Administration of the anti-ASF antibody TLD-1A8A increased the clinical severity and duration of the disease. Consistent with these findings, addition of TLD-1A8A to T cell proliferation assays resulted in up-regulation of the proinflammatory cytokines IL-18 and IL-6 and in down-regulation of IL-10. Furthermore, we identified cytokines that regulated the expression of ASF at both the mRNA and protein level. ASF, therefore, appears to play a previously unappreciated and potentially important role in the regulation of immune responses.

Distribution and immunoregulatory properties of antisecretory factor

Inflammatory processes and the mechanisms by which they are initiated and controlled within the central nervous system (CNS) involve a vast array of cell types and molecules. One cell type believed to be involved in the control of inflammation in the CNS is the microglial cell. The TLD antibodies are a panel of monoclonal antibodies reactive to rat microglial antigens. One antibody from this panel, clone TLD-1A8A, is specific for antisecretory factor (ASF). ASF is a previously identified protein characterized as a potent inhibitor of enterotoxin-induced intestinal fluid secretion. Our results extend the function of this molecule to include the regulation of immune reactions. Administration of TLD-1A8A to T-cell proliferation or mixed leukocyte response assays resulted in increased proliferation of T cells. Flow cytometric analysis indicates that ASF is expressed on macrophages, B cells and dendritic cells, but not on T cells or granulocytes. Immunohistochemical analysis indicates that ASF is expressed by macrophages and cells of dendritic morphology in the spleen, thymus, lymph nodes, Peyer's patch, and in the perivascular area in the CNS. Furthermore, Western blot analysis indicates that ASF is expressed in many tissues including all secondary lymphoid organs. These data suggest that ASF may have a previously unsuspected role in regulating the immune system.

Exacerbation of experimental autoimmune encephalomyelitis in rodents infected with murine gammaherpesvirus-68

Viral infections have long been suspected to play a role in the pathogenesis of multiple sclerosis. In the present study, two different rodent models of experimental autoimmune encephalomyelitis (EAE) were used to demonstrate the ability of murine gammaherpesvirus-68 (gammaHV-68) to exacerbate development of neurological symptoms. SJL mice received UV-inactivated gammaHV-68 or intranasalgammaHV-68, followed by immunization against proteolipid-protein peptide 139-151. Infected mice became moribund within 10 days post-immunization, whereas mice exposed to UV-inactivated gammaHV-68 recovered. In the second model, Lewis rats were exposed to UV-inactivated gammaHV-68 or to gammaHV-68, followed by passive transfer of encephalitogenic T lymphocytes specific for myelin basic protein. Consistently, infected rats had higher clinical scores, and this result was observed during acute or latent gammaHV-68 infection. It is unlikely that this gammaHV-68-induced exacerbation was due to significant viral replication within the central nervous system since nested PCR, viral plaque assays, and infectious-centers assays demonstrated no detectable virus in spinal cords or brains of infected rodents undergoing EAE. Taken together, these studies demonstrate increased clinical symptoms of EAE in rodents infected by a gammaherpesvirus that has a limited ability to invade the central nervous system.

Factors modifying the migration of lymphocytes across the blood-brain barrier

Characterising the factors that control the entry of leucocytes into tissue in response to inflammatory or microbial insult continues to generate considerable interest. Of all the tissues studied it is probably that of the CNS which is the most fascinating because of the specialised properties of its blood vessel walls, which constitute the blood-brain barrier (BBB). In health, very few leucocytes penetrate the BBB but in disorders such as MS the barrier becomes compromised with the result that there is an intense infiltration of the CNS by T lymphocytes whose subsequent activity appears to underlie the onset and progression of disease. The purpose of this article is to summarise and assess recent literature pertaining to how lymphocytes bind to cerebral endothelial cells, migrate across the blood vessel walls and enter the CNS parenchyma. Particular emphasis is devoted to the cellular and molecular aspects of these events and addressing the questions of whether certain subsets of circulating T lymphocytes are more favourably disposed than others to CNS infiltration and whether entry is dependent upon the initial expression of distinct groups of adhesion molecules and upon the generation of chemotactic factors. This article also focuses upon identifying the key stages of lymphocyte migration across the BBB and their susceptibility to antagonism by therapeutic agents. It is intended that the review will provide a useful source of information and offer additional insights into the mechanisms controlling lymphocyte passage across the BBB during pathological disturbance.