Neuroinflammation responses and neurodegeneration in multiple sclerosis

Diffuse neurodegeneration is now considered to be the main cause of irreversible neurological disability in multiple sclerosis (MS). Demonstration of a diffuse inflammatory reaction in the MS brain led to the assumption that diffuse neuroinflammation induces diffuse neurodegeneration. Macrophages/microglia accumulate throughout the MS brain and are, therefore, considered the main culprits implicated in the development of neurodegeneration. However, recent advances in the understanding of macrophage/microglia functions and origins have now challenged that view. This report is a summary of these advances, and discusses their contribution to the perception of macrophage/microglia functions in MS-associated neurodegeneration.

[Porous matrix and primary-cell culture: a shared concept for skin and cornea tissue engineering]

Skin and cornea both feature an epithelium firmly anchored to its underlying connective compartment: dermis for skin and stroma for cornea. A breakthrough in tissue engineering occurred in 1975 when skin stem cells were successfully amplified in culture by Rheinwald and Green. Since 1981, they are used in the clinical arena as cultured epidermal autografts for the treatment of patients with extensive burns. A similar technique has been later adapted to the amplification of limbal-epithelial cells. The basal layer of the limbal epithelium is located in a transitional zone between the cornea and the conjunctiva and contains the stem cell population of the corneal epithelium called limbal-stem cells (LSC). These cells maintain the proper renewal of the corneal epithelium by generating transit-amplifying cells that migrate from the basal layer of the limbus towards the basal layer of the cornea. Tissue-engineering protocols enable the reconstruction of three-dimensional (3D) complex tissues comprising both an epithelium and its underlying connective tissue. Our in vitro reconstruction model is based on the combined use of cells and of a natural collagen-based biodegradable polymer to produce the connective-tissue compartment. This porous substrate acts as a scaffold for fibroblasts, thereby, producing a living dermal/stromal equivalent, which once epithelialized results into a reconstructed skin/hemicornea. This paper presents the reconstruction of surface epithelia for the treatment of pathological conditions of skin and cornea and the development of 3D tissue-engineered substitutes based on a collagen-GAG-chitosan matrix for the regeneration of skin and cornea.

Bone marrow CD34+/B220+ progenitors target the inflamed brain and display in vitro differentiation potential toward microglia

Recent evidence indicates that microglial cells may not derive from blood circulating mature monocytes as they express features of myeloid progenitors. Here, we observed that a subpopulation of microglial cells expressed CD34 and B220 antigens during brain development. We thus hypothesized that microglia, or a subset of microglial cells, originate from blood circulating CD34+/B220+ myeloid progenitors, which could target the brain under developmental or neuroinflammatory conditions. Using experimental allergic encephalomyelitis (EAE) as a model of chronic neuroinflammation, we found that a discrete population of CD34+/B220+ cells expands in both blood and brain of diseased animals. In EAE mice, intravenous transfer experiments showed that macrophage-colony stimulating factor (M-CSF) -expanded CD34+ myeloid progenitors target the inflamed central nervous system (CNS) while keeping their immature phenotype. Based on these results, we then assessed whether CD34+/B220+ cells display in vitro differentiation potential toward microglia. For this purpose, CD34+/B220+ cells were sorted from M-CSF-stimulated bone marrow (BM) cultures and exposed to a glial cell conditioned medium. Under these experimental conditions, CD34+/B220+ cells were able to differentiate into microglial-like cells showing the morphological and phenotypic features of native microglia. Overall, our data suggest that under developmental or neuroinflammatory conditions, a subpopulation of microglial cells derive from CNS-invading CD34+/B220+ myeloid progenitors.

Expression of the anaphylatoxin C5a receptor in the oligodendrocyte lineage

Expression of the C5a receptor in the central nervous system has been demonstrated on microglia, astrocytes and neurons. In the present study, we demonstrate C5aR expression in vitro by rat and murine O2-A progenitor cells and oligodendrocytes. We also observed that in vitro differentiation of O2-A progenitors into mature oligodendrocytes is accompanied by down-regulation of C5aR mRNA expression. These results suggest that the C5aR may be a marker for oligodendroglial differentiation and play a role in oligodendrocyte function.

Attenuation of experimental autoimmune demyelination in complement-deficient mice

The exact mechanisms leading to CNS inflammation and myelin destruction in multiple sclerosis and in its animal model, experimental allergic encephalomyelitis (EAE) remain equivocal. In both multiple sclerosis and EAE, complement activation is thought to play a pivotal role by recruiting inflammatory cells, increasing myelin phagocytosis by macrophages, and exerting direct cytotoxic effects through the deposition of the membrane attack complex on oligodendrocytes. Despite this assumption, attempts to evaluate complement's contribution to autoimmune demyelination in vivo have been limited by the lack of nontoxic and/or nonimmunogenic complement inhibitors. In this report, we used mice deficient in either C3 or factor B to clarify the role of the complement system in an Ab-independent model of EAE. Both types of complement-deficient mice presented with a markedly reduced disease severity. Although induction of EAE led to inflammatory changes in the meninges and perivascular spaces of both wild-type and complement-deficient animals, in both C3(-/-) and factor B(-/-) mice there was little infiltration of the parenchyma by macrophages and T cells. In addition, compared with their wild-type littermates, the CNS of both C3(-/-) and factor B(-/-) mice induced for EAE are protected from demyelination. These results suggest that complement might be a target for the therapeutic treatment of inflammatory demyelinating diseases of the CNS.

Central nervous system-targeted expression of the complement inhibitor sCrry prevents experimental allergic encephalomyelitis

Although generally thought of as a T cell-driven autoimmune disease, recent studies in experimental allergic encephalomyelitis (EAE), the animal model of multiple sclerosis, suggest a significant role for innate immune mechanisms. To address the possibility that the complement system plays a central role in these diseases, we developed a transgenic mouse with astrocyte-targeted production of a soluble inhibitor of complement activation, complement receptor-related protein y (sCrry). Here, we show that sCrry transgenic mice are either fully protected against EAE or develop significantly delayed clinical signs. These results indicate that complement activation may have an essential role in the pathogenesis of the disease and that complement-mediated events may occur early during the effector phase of EAE. Furthermore, this work underscores the importance of humoral immunity in amplifying a T cell-initiated pathogenic process.

Complement anaphylatoxin receptors on neurons: new tricks for old receptors?

Activation of the complement system has been reported in a variety of inflammatory diseases and neurodegenerative processes of the CNS. Recent evidence indicates that complement proteins and receptors are synthesized on or by glial cells and, surprisingly, neurons. Among these proteins are the receptors for the chemotactic and anaphylactic peptides, C5a and C3a, which are the most-potent mediators of complement inflammatory functions. The functions of glial-cell C3a and C5a receptors (C3aR and C5aR) appear to be similar to immune-cell C3aRs and C5aRs. However, little is known about the roles these receptors might have on neurons. Indeed, when compared with glial cells, neurons display a distinct pattern of C3aR and C5aR expression, in either the normal or the inflamed CNS. These findings suggest unique functions for these receptors on neurons.

Expression of the murine complement regulatory protein crry by glial cells and neurons

The expression of the murine complement regulatory protein, Crry, in the CNS remains largely unexplored. In this study, we examined murine astrocytes and microglia purified from neonatal brain and sections of adult murine brain for the expression of Crry. Using RT-PCR, immunohistochemistry, in situ hybridization, flow cytometry, and Western blot analysis, we demonstrated that astrocytes and microglia express Crry protein and RNA. Crry expression is greater on microglia than astrocytes and, as determined by Western blot analysis, each cell type expresses a Crry protein of different molecular weight. Interestingly, neuronal expression of Crry was seen only at the RNA level. These data demonstrate Crry expression by astrocytes, microglia, and neurons in the murine CNS and suggest that Crry may play an important role in protecting the CNS against complement-mediated damage.

Human T cells express the C5a receptor and are chemoattracted to C5a

The anaphylatoxin C5a is a potent mediator of inflammation that exerts a broad range of activity on cells of the myeloid lineage. In this study, we present the first evidence that human T cells express the C5a receptor (C5aR) and are chemotactic to C5a. Using FACS analysis, we found that the C5aR was expressed at a low basal level on unstimulated T cells and was strikingly up-regulated upon PHA stimulation in a time- and dose-dependent manner. CD3+ sorted T cells as well as Jurkat T cells were shown to express C5aR mRNA as assessed by RT-PCR. Moreover, semiquantitative RT-PCR analysis demonstrated that C5aR mRNA was down-regulated in purified T cells upon long-term PHA stimulation. To demonstrate that C5a was biologically active on T cells, we investigated the chemotactic activity of C5a and observed that purified CD3+ T cells are chemotactic to C5a at nanomolar concentrations. Finally, using a combination of in situ hybridization and immunohistochemistry, we showed that the T cells infiltrating the central nervous system during experimental allergic encephalomyelitis express the C5aR mRNA. In summary, these results suggest that C5a exerts direct effects on T cells and could be involved in the trafficking of T cells under physiological and pathological conditions, including inflammatory diseases of the central nervous system.

Kinetics of anaphylatoxin C5a receptor expression during experimental allergic encephalomyelitis

In this study, we investigated the expression of the C5aR in spinal cords of Lewis rats with experimental allergic encephalomyelitis (EAE). Using in situ hybridization (ISH) we analyzed the kinetics of C5aR at different time points of EAE (preclinical stage, clinical peak, remission phase). We observed that C5aR mRNA was readily detected in the CNS of EAE rats at all the stages of the disease. Using a combination of ISH and immunohistochemistry, we formally demonstrated that C5aR is strongly expressed on microglial cells and hypertrophic astrocytes during EAE. The potential involvement of C5a receptor in EAE physiopathology is discussed.

Abnormalities of cardiac repolarization in multiple sclerosis: relationship with a model of allergic encephalomyelitis in rat

Ventricular repolarization was investigated for the first time in 48 multiple sclerosis (MS) patients using measurement of QTc interval on standard electrocardiographic recordings. The repolarization process was prolonged significantly in MS compared to control subjects (P = 0.0001). This result was confirmed with an animal model of MS, i.e., the experimental allergic encephalomyelitis in rat. The contribution of prolonged QT to syncopal attack or sudden cardiac death in MS patients need further investigation.

Low affinity NGF receptor expression in the central nervous system during experimental allergic encephalomyelitis

In the central nervous system (CNS), p75, or low-affinity nerve growth factor receptor (LNGFR), is assumed to play a critical role in mediating the effects of neurotrophins on neuronal survival. Recent studies have shown that nerve growth factor (NGF) can act also on immune cells through its binding to p75. Using immunohistochemistry, we have investigated the expression of the p75 receptor in the CNS during chronic relapsing experimental allergic encephalomyelitis (EAE) of the Lewis rat, an animal model of multiple sclerosis (MS). We report here a sequential expression of p75, first in Purkinje cells during the first attack, and secondly on both endothelial and perivascular cells in the latter stages of the disease. Moreover, starting from the second attack, p75 was also expressed on glial ensheathing cells, likely myelinating cells, located primarily in the dorsal roots. These data suggest that during EAE, LNGFR may play an important role in leukocyte-endothelial cell interactions and in the maintenance of Purkinje cells survival.

1,25-Dihydroxyvitamin D3 inhibits the expression of inducible nitric oxide synthase in rat central nervous system during experimental allergic encephalomyelitis

The inducible form of nitric oxide synthase (iNOS) generates nitric oxide of which the excessive production is associated with central nervous system (CNS) inflammatory diseases. The investigation of iNOS expression during experimental allergic encephalomyelitis (EAE) of the Lewis rat demonstrated iNOS immunoreactivity and mRNA both during inflammatory bursts (days 12 and 23 post-immunization) and during the remission phase (day 18). iNOS expression was region-specific and expanded with time along a caudo-rostral axis, thus, correlating with the development of inflammatory infiltrates. Whereas cells of the monocyte/macrophage lineage continuously contributed to iNOS expression, astrocytes only expressed iNOS immunoreactivity or mRNA during the relapse (day 23). In order to investigate possible regulatory effects of 1,25-dihydroxyvitamin D3 (1,25-D3) on iNOS expression, rats were treated with the hormone after the beginning of clinical signs (days 11, 13, 19, 21 and 23 post-immunization), and areas of the CNS were examined at day 23. 1,25-D3 exerted a drastic inhibitory effect on iNOS expression, both at the protein and the mRNA levels. However, this effect was region-specific, and was most pronounced in the cerebellum and brainstem, but non-existent in cerebral cortex. iNOS down-regulation occurred in macrophages, activated microglia and astrocytes. The inhibition of iNOS expression in some CNS structures could account for the improvement of clinical signs observed in EAE-rats treated with 1,25-D3. Since 1,25-D3 can be synthesized by activated macrophages or microglia, our results support the hypothesis that this hormone might be implicated in the control of the CNS-specific immune responses. 1,25-D3 or its analogues could, thus, be of therapeutic value in the management of iNOS-associated diseases of the CNS.

1,25 Dihydroxyvitamin D3 exerts regional effects in the central nervous system during experimental allergic encephalomyelitis

1,25-dihydroxyvitamin D3 (1,25-D3) is already known to prevent clinical signs of experimental allergic encephalomyelitis when animals are treated during the immunization phase. In the present work we have evaluated the ability of 1,25-D3 to inhibit chronic relapsing experimental allergic encephalomylitis (EAE) of the Lewis rat, when administered after the beginning of clinical signs. We observed a significant clinical improvement in 1,25-D3-treated rats. This effect was accompanied by a profound inhibition of CD4 antigen expression by central nervous system (CNS) infiltrating monocytes/macrophages and parenchymal microglia. In addition, immunohistochemical analysis performed at the time of the second attack evidenced a region-specific distribution of inflammatory cells. In the same way, some aspects of the effects exerted by 1,25-D3 appeared to vary depending on the region considered, namely spinal cord, brainstem, cerebellum, midbrain or anterior brain. Thus, in 1,25-D3-treated rats, we observed an almost complete inhibition of CD4 antigen expression in the granule cell layer and the adjacent white matter of the cerebellum as well as a marked decrease in the number of OX42-positive cells (macrophages and activated microglia) in anterior brain sections. We conclude that 1,25-D3 can exert immunomodulatory effects inside the CNS during an ongoing immune process and may thus represent a promising therapy for multiple sclerosis.

Pentoxifylline inhibits experimental allergic encephalomyelitis

Pentoxifylline, a widely used methylxanthine, has been proven to inhibit the production and action of the cytokine TNF alpha. Since it has been suggested that TNF alpha is the major cytokine involved in the pathogenesis of multiple sclerosis, we tested pentoxifylline for its capacity to prevent experimental allergic encephalomyelitis (EAE). 26 Lewis rats with acute EAE were treated with either pentoxifylline or saline. The pentoxifylline treated rats showed a significantly lower incidence of clinical signs as well as significantly lower histological inflammation. The exact mechanism of this preventive effect remains to be clarified but it might be mainly related to inhibition of TNF alpha release from central nervous system macrophages.

[Kidney transplantation and HLA-DR compatibility evaluated by genomic analysis: one center study]

The actual effect of HLA-DR matching in renal transplantation remains controversial. Since DNA analysis has been shown to be more reliable than serological typing, a re-evaluation of the impact of DR-matching on graft prognosis is required. In this study, 224 cadaver kidney transplantations performed in our center were retrospectively matched according to Restriction Fragment Length Polymorphism DR incompatibilities and compared to prospective serological DR-matching. Transplant outcome was evaluated using graft survival, first rejection onset and rejection frequency. In 18.8% individuals, a discrepancy between serology and DNA typing for at least one antigen was noted. Serology particularly failed to type recipients (21.7%) and 43.2% of the total missed antigens were serologically "blank" or unidentified ("X") alleles. A graft survival rate of 100% after one year was observed for transplantations with no DNA DR mismatch (n = 31). Furthermore, there was a definite correlation between DNA matching and (i), the percentage of individuals with one or more than one acute rejection episode (18% and 41.8% at one year for O incompatibility and pooled 1 and 2 incompatibilities respectively, p < 0.05); (ii), the mean of acute rejection per individual (p < 0.001); and (iii), the rejection onset time (p < 0.01). No correlation between serological matching and the acute rejection episodes parameters was noted. Since HLA typing could be performed in less than 2 hrs using new molecular biology techniques, we conclude that prospective DNA typing should improve kidney transplantation outcome in the near future.