Brain, Vol. 124, No. 8, 1544-1554,
August 2001
© 2001 Oxford University Press
Bacterial peptidoglycan and immune reactivity in the central nervous system in multiple sclerosis
1 Departments of Immunology and 2 Neurology, Erasmus University and University Hospital Rotterdam-Dijkzigt, Rotterdam and 3 Netherlands Brain Bank, Amsterdam, The Netherlands
Correspondence to:
J. D. Laman, Department of Immunology, Erasmus University, Rotterdam, PO Box 1738, 3000 DR Rotterdam, The Netherlands E-mail: laman{at}immu.fgg.eur.nl
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Abstract |
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Multiple sclerosis is believed to result from a CD4+ T-cell response against myelin antigens. Peptidoglycan, a major component of the Gram-positive bacterial cell wall, is a functional lipopolysaccharide analogue with potent proinflammatory properties and is conceivably a mediator of sterile inflammation. Here we demonstrate that peptidoglycan is present within antigen-presenting cells in the brain of multiple sclerosis patients. These cells have macrophage and dendritic cell characteristics, and are immunocompetent as evidenced by co-expression of inflammatory cytokines and co-stimulatory molecules. In addition, intrathecal plasma cells specific for peptidoglycan are present in multiple sclerosis brain tissue, and antibodies binding peptidoglycan are present in CSF during active disease. Peptidoglycan may thus contribute to T- and B-cell activity during brain inflammation without a requirement for local bacterial replication.
multiple sclerosis; peptidoglycan; cytokines; antigen-presenting cells; antibodies
ELISA = enzyme-linked immunosorbent assay; LPS = lipopolysaccharide; Mab = monoclonal antibody; NAMLAA = N-acetyl muramyl L-alanine amidase; PG = peptidoglycan
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Introduction |
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TopAbstractIntroductionPatients and methodsResultsDiscussionAcknowledgementsReferences |
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According to prevailing dogma, multiple sclerosis is caused by autoreactive CD4+ T cells specific for myelin components with a proinflammatory T helper phenotype (Lassmann, 1998
). Since healthy donors have similar numbers of myelin-reactive T cells to patients, additional factors are clearly needed to promote (auto)-reactivity of T cells within the CNS (Lassmann and Wekerle, 1998). Recent studies in several experimental models, including the experimental autoimmune encephalomyelitis model for multiple sclerosis, have shown that various infectious and proinflammatory agents such as lipopolysaccharide (LPS) are capable of reversing the tolerant state of CD4+ and CD8+ T cells (Röcken et al., 1992; Vella et al., 1995; Segal et al., 1997; Ehl et al., 1998). Activation of these cells is crucially dependent on the presence of both the stimulatory agent and the specific (auto)-antigen (Ehl et al., 1998). Research on inflammatory properties of bacterial antigens in brain tissue has shown that bacteria injected into the brain parenchyma are able to induce inflammatory responses only after peripheral sensitization of T cells (Matyszak, 1998). However, there is no clear evidence to date that bacterial agents or components derived thereof, such as LPS, are functionally involved in initiation or perpetuation of multiple sclerosis disease activity. In addition, studies attempting to link infectious agents to (autoimmune) inflammation are often based on the premise that replication occurs within the affected organ (Relman, 1999), but this is not necessarily the case.
Peptidoglycan (PG) is a major constituent of the cell wall of Gram-positive bacteria, which are abundantly present at all mucosa, and most prominently in the gut as part of the normal microbial flora (for review, see Hamann et al., 1998). PG is composed of long sugar chains of alternating N-acetyl glucosamine and N-acetyl muramic acid residues, which are interlinked by peptide bridges, resulting in a large complex macromolecular structure (Schleifer and Kandler, 1972). PG is only a very minor constituent of the cell wall of Gram-negative bacteria. PG can be regarded as a functional analogue of LPS, and both molecules activate innate immune defence mechanisms (Hoffmann et al., 1999). First, both molecules use CD14 on monocytes/macrophages and granulocytes as their cellular receptor, differentially engaging the recently identified Toll-like receptors (Medzhitov et al., 1997; Schwandner et al., 1999; Ulevitch, 1999). Secondly, the intracellular signalling pathways employed by both molecules are highly similar if not identical (Mattsson et al., 1996; Hamann et al., 1998; Gupta et al., 1999). Thirdly, both LPS and PG induce strong proinflammatory responses in vitro, including production of cytokines such as IL-1 and TNF-
(Weidemann et al., 1994; Gupta et al., 1999; Le Roy et al., 1999). LPS and PG are complex macromolecules which are difficult to digest by phagocytes (Forestier et al., 1999). Macrophages lack amidase (N-acetyl muramyl L-alanine amidase, NAMLAA) expression (Hoijer et al., 1996, 1997a) which is required for full degradation of PG in joint action with lysozyme (Hoijer et al., 1997b). This resistance to degradation explains, at least in part, the persistence of microbial cell walls, which may be a pivotal factor in chronic (autoimmune) inflammation (Relman, 1999).
Antigen-presenting cells containing PG are present in the joints of patients with rheumatoid arthritis, possibly contributing to the local inflammatory environment (Hazenberg, 1995; Melief et al., 1995). Interestingly, PG retaining proinflammatory capacity such as the induction of TNF- and IL-1, can be fractionated from sterile human spleen (Timmerman et al., 1993; Weidemann et al., 1994; Schrijver et al., 1999), suggesting that continuous redistribution of PG occurs from the mucosa to the secondary lymphoid organs, as well as to other anatomical sites in the absence of sepsis, and without requirement for local bacterial replication. This is fully consistent with the presence of circulating leucocytes carrying PG in human healthy subjects (Lehtonen et al., 1995) and distinct patient categories (Lehtonen et al., 1997).
In view of the strong influx of macrophages into the CNS of multiple sclerosis patients facilitated by severely impaired blood–brain barrier function (de Vries et al., 1997), we hypothesized that phagocytic antigen-presenting cells carrying PG gain access to the CNS and can locally promote immune reactivity of T and B cells. Here we show that PG-containing antigen-presenting cells are present in human multiple sclerosis brain tissue, and that they express co-stimulatory molecules and immunomodulatory cytokines. In addition, antibody forming cells specific for PG are present in human multiple sclerosis brain tissue and patients with active disease have antibodies against PG in the CSF. These findings suggest that PG affects immune reactivity in the brain.
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Patient samples
Human brain tissue taken at autopsy was provided by the Netherlands Brain Bank in Amsterdam (Coordinator Dr R. Ravid). Average post-mortem delay was 6 h (range 4–9 h) for multiple sclerosis patients and 8 h (range 6–10 h) for control patients. No abnormalities could be detected at autopsy in the brain tissues of the control subjects who died owing to different causes, e.g. cardiac arrest, cancer and pneumonia. Patient features are shown in Table 1
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CSF samples of 10 multiple sclerosis patients and 10 control patients were obtained from the Department of Neurology of the Erasmus University and University Hospital Rotterdam-Dijkzigt. CSF samples of relapsing–remitting multiple sclerosis patients were taken prior to immunomodulating therapy during a relapse of multiple sclerosis. Control subjects were patients who presented with severe headache for which no cause could be determined.
Immunohistochemistry
Immunohistochemical procedures used for detection of cellular subsets, antigens, antigen specific plasma cells, co-stimulatory molecules and cytokines in frozen sections have all been described in detail previously (Claassen and Jeurissen, 1998; Schrijver et al., 2000). The frozen sections were fixed in acetone with 0.5% H2O2 for 10 min. Antibodies used are shown in Table 2. To detect specific antibody forming cells, peptidoglycan–polysaccharide isolated from human faeces (Hazenberg et al., 1989) was labelled with biotin (Laman et al., 1990; Claassen et al., 1992). Sections from reactive human tonsils were included on each individual object slide to provide internal positive control tissue. Sections were evaluated by two independent observers blinded to the staining procedure.
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Monoclonal antibody (Mab) against peptidoglycan (2E9)
2E9 is a murine Mab (IgG3) raised against a pure fraction of peptidoglycan-polysaccharides isolated from normal human faeces (Kool et al., 1994
). The specificity of this Mab has been extensively investigated and confirmed. First, inhibition studies using enzyme-linked immunosorbent assay (ELISA) show that 2E9 recognizes cell wall fragments, muramyl dipeptide and lysozyme-solubilized cell walls of different Gram-positive bacteria (Kool et al., 1994). These experiments suggest that it binds to the glycan backbone of PG since muramic acid forms part of the structure recognized. Secondly, spleen sections of germ-free rats and of neonatal rats in which the gut flora has not been established yet, display no PG-containing phagocytes, whereas spleens of adult rats do. In addition, intravenous injection of PG into neonatal rats results in binding of 2E9 to phagocytes in spleen sections (Kool et al., 1994). Thirdly, immunoelectron microscopy shows that Mab 2E9 binds to cell walls of Staphylococcus epidermidis surviving intracellularly in macrophages around infected biomaterial. Fourthly, 2E9 displays no detectable reactivity against >10 000 random dodecapeptides and 8000 tripeptides in Pepscan approaches (Slootstra et al., 1997), confirming this Mab has very low crossreactivity with non-PG epitopes. An isotype-matched control antibody (NS7, IgG3) of irrelevant specificity (sheep red blood cells) was used throughout the studies and displayed no binding activity in brain tissue of multiple sclerosis patients or control subjects.
Statistical analysis
The number of PG-containing cells and plasma cells binding PG present in multiple sclerosis brain tissue and control brain tissue were compared using the Mann-Whitney rank-sum test. A P value <0.05 was considered to be significant.
PG ELISA
To measure anti-PG antibodies in CSF, an ELISA, extensively validated and used before, was performed as described (Hazenberg et al., 1990). Briefly, 50 µl of peptidoglycan–polysaccharides (10 µg/ml ) was coated overnight at 50°C onto 96-well polystyrene microtitre plates. Aliquots (100 µl) of 1 : 2, 1 : 4 and 1 : 8 dilutions of CSF were incubated during 1 h at 37°C. As detecting antibody, peroxidase conjugated rabbit anti-human IgM, IgG or IgA (Jackson Immunoresearch, Inc., Westgroove, Pa., USA) was used for 1 h at 37°C. The development of the colorimetric assay took place at 37°C for 30–45 min after the addition of 100 ml of ortho-phenylenediamine/H2O. The reaction was stopped by 4 M H2SO4 and the optical density was measured at a wavelength of 492 nm with a Titertek Multiskan (Flow Laboratories, Irvine, Scotland). Between all incubation steps the plates were washed three times with PBS (phosphate-buffered saline)–0.02% Tween and CSF and conjugates were diluted in PBS–0.2% Tween.
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Results |
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PG-containing cells are present in multiple sclerosis brain tissue
The presence of PG was analysed in cryo-sections of brain white matter of multiple sclerosis patients and control subjects using a monoclonal antibody against PG (Kool et al., 1994
). The numbers of PG-containing cells were significantly higher in tissue from multiple sclerosis brains compared with control patients (Fig. 1) (P = 0.001). In multiple sclerosis patients, PG-containing cells were mainly present on the edge of active lesions (Lassmann et al., 1998) (Fig. 2A), as defined by Oil-red O staining for myelin breakdown products ingested by macrophages. Furthermore, PG-containing cells were present around blood vessels, or scattered in the normal appearing white matter (Fig. 2B). Only rarely could PG-containing cells be found within the fully demyelinated foci forming the centre of lesions. To further analyse the role of PG-containing cells in inflammation of the brain, double labelling was performed on brain tissue of multiple sclerosis patients selected for high numbers of PG-containing cells, to determine the phenotype and activation state of the PG-containing cells.
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PG is present in macrophages and dendritic cells
To determine the phenotype of PG-containing cells, co-expression of PG with CD68, CD83, CD14, 27E10, CD1a and CD3 was analysed. Figure 3
shows that PG is mostly present in macrophages expressing CD68 and dendritic cells expressing CD83. CD14, which is the cellular receptor for both PG and LPS present on relatively immature phagocytes, was expressed by 17% (range 0–27%) of the PG-containing cells (Weidemann et al., 1997). The majority of the PG-containing cells (mean 62%), and in two out of nine patients all of these cells (range 33–100%), expressed 27E10, an acute stage inflammatory macrophage marker characteristic for active multiple sclerosis lesions (Brück et al., 1995).
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Although PG is most likely to be presented by HLA molecules, the possibility cannot be excluded that CD1a is involved in the presentation of the carbohydrate molecules present in PG. However, only very few PG-containing cells co-expressed CD1a, suggesting that this mechanism of antigen presentation is highly unlikely for PG.
PG-containing cells co-express co-stimulatory molecules
The capability of PG-containing cells to present antigen was examined by double staining for HLA-DR, CD80/B7–1, CD86/B7–2 and CD40, which are centrally involved in (co)-stimulation of CD4+ T cells. Co-expression with PG occurred for all four molecules to varying extents, in particular for CD80 (Fig. 2C
), suggesting that PG-containing cells are mainly functionally competent, active antigen-presenting cells (Fig. 3).
Peptidoglycan containing cells co-express different cytokines
To assess whether PG-containing cells can contribute to CNS inflammation in multiple sclerosis by producing cytokines, double labelling was performed for proinflammatory cytokines (IL-1 and ß, IL-6, IL-12, TNF- and IFN-
) and immunoregulatory cytokines (IL-4 and IL-10). Except for IL-1, all cytokines analysed were expressed by PG-containing cells, to varying extents. Of the proinflammatory cytokines, co-expression was most frequently found for TNF- (mean 44% of PG-containing cells, range 9–100%). In one patient, all PG-containing cells produced the strongly proinflammatory and myelotoxic cytokine TNF-. In addition, TNF- was also often strongly expressed by cells directly adjacent to PG-containing cells (Fig. 2E). Co-expression of PG was also found for IL-1ß (mean 30%, range 14–52%), IL-6 (mean 11%, range 0–22%), IL-12 (mean 18%, range 0–65%) and IFN- (mean 11%, range 10–73%), although the latter cytokine was mostly expressed by cells directly adjacent to PG-containing cells. Immunoregulatory cytokines were prominently produced by PG-containing cells. IL-4 was detected in 58% (range 13–93%) of PG-containing cells. IL-10 was mainly produced by cells directly juxtaposed with PG-containing cells (Fig. 2D), but co-expression was found in 40% (range 0–83%) of all PG-containing cells.
Antibody forming cells specific for peptidoglycan are present in multiple sclerosis brain tissue
Healthy human subjects have systemic IgM, IgG and IgA levels against PG (Hazenberg et al., 1990), reflecting continuous exposure to Gram-positive bacteria at the mucosa. To determine whether intrathecal antibodies against PG were produced in multiple sclerosis brain tissue, plasma cells specific for PG were visualized in situ using biotin-labelled PG (Laman et al., 1990; Claassen et al., 1992). Plasma cells specific for PG could be detected in seven out of 13 multiple sclerosis patients and in two out of seven controls (Fig. 4). The numbers of plasma cells specific for PG were limited in control patient tissues and three of the multiple sclerosis patients; however, four multiple sclerosis patients had high numbers of PG-specific antibody forming cells. In multiple sclerosis patients, the number of antibody forming cells against PG was directly correlated with the number of PG-containing cells (P < 0.01). Antibody forming cells specific for PG were scattered throughout the tissue (Fig. 2F) and could often be found near blood vessels. Pre-incubation of tissue sections with unlabelled PG resulted in a dose dependent reduction of the number of PG-binding cells, confirming the specificity of staining. Double labelling for CD20, a surface plasma cell marker, IgM, IgG and PG-biotin confirmed that PG-binding cells were indeed plasma cells containing high levels of cytoplasmic immunoglobulin.
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Antibodies specific for peptidoglycan are present in CSF of patients with active multiple sclerosis
To confirm our finding of intrathecal production of antibodies against PG in situ in multiple sclerosis autopsy brain tissue, ELISA was used to determine IgM, IgG and IgA antibody levels against PG in CSF samples. Samples taken during relapse from relapsing–remitting multiple sclerosis patients not treated with immunosuppressive drugs were compared with samples from patients with severe headache for which no cause could be determined. Anti-PG antibodies could not be detected in any of the control patients. Using conservative cut-off values, six out of 10 multiple sclerosis patients displayed considerable levels of anti-PG antibodies of the IgG and/or IgA isotypes (Fig. 5
).
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Discussion |
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TopAbstractIntroductionPatients and methodsResultsDiscussionAcknowledgementsReferences |
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The current study shows that antigen-presenting cells in the CNS of multiple sclerosis patients contain the Gram-positive cell wall constituent peptidoglycan, which is abundantly present at all mucosal surfaces. In the CNS, PG may contribute to inflammation by induction of cytokine secretion, modulating T-cell function and stimulating antibody formation.
The presence of bacterial peptidoglycan in CNS tissue sheds a different light on the search for infectious agents involved in multiple sclerosis, where the emphasis has been on identification of viruses (e.g. HHV-6) and not on bacteria (Soldan et al., 1997; Noseworthy, 1999). The implicit assumption of such approaches is that local replication of viruses or bacteria is essential. In sharp contrast, we show that peptidoglycan may stimulate CNS-inflammation in the apparent local absence of viable bacteria and replication, implying that this antigen can be a microbial mediator in sterile inflammation. Thus, our data support novel emerging insights that persistence of bacterial cell wall antigens can contribute to autoimmune diseases (Relman, 1999).
Studies of autopsy brain material and multiple sclerosis routinely and consistently reveal a partial overlap of pathological characteristics between patient and control subject tissues (Ravid et al., 1995). For example, activated macrophages can be found in control subject tissues (Purba et al., 1993). This also explains why limited numbers of PG-positive cells could be detected in control tissues in the current study.
Peptidoglycan is present in functionally competent antigen-presenting cells
Characterization of PG-containing cells showed that macrophages containing PG were mostly mature, while only a minority had an immature phenotype. The persistence of PG in macrophages can be explained by the fact that amidase cannot be detected in macrophages (Hoijer et al., 1997a). High expression of NAMLAA (Hoijer et al., 1996, 1997a) is required for full degradation of PG in joint action with lysozyme (Hoijer et al., 1997b). The high percentage of 27E10 expression by PG-containing cells indicated that PG is present in active lesions (Brück et al., 1995), of which 27E10 is a reliable marker. This is consistent with the concept that antigen-presenting cells mature upon uptake of antigen and migration (Mellman et al., 1998), where migration through vascular endothelium is a crucial step promoting functional maturity and loss of surface markers such as CD14 (Randolph et al., 1998). CD14+ monocytes can also mature into dendritic cells, a transition enhanced by bacterial stimuli (Rescigno et al., 1999), which may explain the presence of PG in a limited number of dendritic cells.
The expression of HLA-DR, CD40, CD80 and CD86 by PG-containing cells indicates that these cells may be potent stimulators of antigen-specific T-cell activation. In vitro analysis of PG isolated from human tissues has shown that PG is able to induce T-cell proliferation (unpublished results). In addition, PG-containing cells synthesized cytokines involved in regulation of inflammatory activity (e.g. IL-1ß, IL-6, IL-12, TNF-, IFN-, IL-4 and IL-10), demonstrating that they produce soluble mediators directly affecting T-cell proliferation, activation and survival (Vella et al., 1995, 1997). PG isolated from sterile human spleen is capable of inducing IL-1, IL-6 and TNF- (Schrijver et al., 1999) by macrophages in vitro; IL-10, IFN- and IL-12 and gelatinase B are also induced upon PG stimulation in vitro (Schrijver et al., 2001a). This confirms that PG can indeed be responsible for the cytokine production by the PG-containing cells in the CNS.
Peptidoglycan and T-cell tolerance
We hypothesize that PG in the CNS may contribute to breaching T-cell tolerance and promotes T-cell activity by antigen presentation and induction of cytokine production (Röcken et al., 1992; Vella et al., 1995; Segal et al., 1997; Ehl et al., 1998). This is supported by the expression of HLA-DR, co-stimulatory molecules and cytokines by PG-containing cells in multiple sclerosis brain tissue. It has been shown in animal models that inflammatory processes created by bacterial infections or LPS lead to activation of autoreactive CD4+ cells (Röcken et al., 1992) or CD8+ cells (Ehl et al., 1998) which otherwise die by apoptosis. The major mechanism leading to breaking of tolerance is cytokine induction by infectious agents leading to T-cell survival (Vella et al., 1995, 1998). This view is supported by the finding that LPS induces experimental autoimmune encephalomyelitis in mice injected with myelin basic protein-specific T cells through induction of IL-12 (Segal et al., 1997). Therefore, the presence and persistence of PG in brain tissue may promote loss of tolerance against autoantigens present in the brain, e.g. myelin basic protein, proteolipid protein and others.
Intrathecal antibody synthesis against peptidoglycan
Plasma cells producing antibody specific for PG were also present in situ in multiple sclerosis brain tissue. This demonstrates that intrathecal antibody production against PG occurs. To confirm this finding, CSF of multiple sclerosis patients and control patients was analysed, showing that none of the control patients had specific antibody titres, whereas the majority of multiple sclerosis patients had detectable specific IgG and IgA levels. The presence of antibodies in the CSF may be partly due to leakage from the blood, but the presence of plasma cells specific for PG within the brain tissue unequivocally demonstrates that antibodies specific for PG are also produced intrathecally. The specificity and pathological relevance of plasma cells in the brain and oligoclonal immunoglobulins in multiple sclerosis has been highly obscure thus far (see Cortese et al., 1998). Our finding that PG evokes specific intrathecal antibody production in situ identifies a hitherto unknown specificity of local plasma cells.
Perspective
In conclusion, this study suggests that immunocompetent PG-containing cells are able to reach the brain in multiple sclerosis and may contribute to local immune reactivity, by expression of co-stimulatory molecules and cytokines, and by stimulating intrathecal antibody formation. We do not propose a single antigen–disease link. Instead we suggest that PG may be a crucial mediator in polymicrobial involvement during chronic inflammatory disease (see Relman, 1999). Redistribution of PG from mucosal sites to the brain depends on the intricate interplay between several factors such as the permeability of the intestine, activity of enzymes specifically involved in PG degradation (Hoijer et al., 1997a) and mucosal and systemic antibody responses against PG (Schrijver et al., 2001b). Restricting the access of PG to non-mucosal sites could therefore be of clinical benefit to patients, as this may lead to lower levels of inflammation.
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Acknowledgements |
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The authors wish to thank Drs R. Hintzen and D. Swaab for critical reading of this manuscript. Patient tissue samples and additional pathology information were provided by the Netherlands Brain Bank, Amsterdam, Dr B. C. Jacobs (Department of Neurology, University Hospital Rotterdam-Dijkzigt, Rotterdam) and Dr C. J. A. de Groot (Department of Pathology, Free University, Amsterdam). T. M. van Os is acknowledged for microphotography and preparing the figures. This study was in part supported by grants from NWO-NDRF (940–70–007), the EC Biomed-2 programme (BMT 97–2131), The Netherlands Foundation for the Support of Multiple Sclerosis Research (RSOE, Rotterdam Study on Exacerbations, 95–207) and the `Hersenstichting Nederland' [HSN 7F99(2).49].
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References |
|---|
|
TopAbstractIntroductionPatients and methodsResultsDiscussionAcknowledgementsReferences |
|---|
Brück W, Porada P, Poser S, Rieckmann P, Hanefeld F, Kretzschmar HA, et al. Monocyte/macrophage differentiation in early multiple sclerosis lesions. Ann Neurol 1995; 38: 788–96.[ISI][Medline]
Claassen E, Jeurissen SHM. A step by step guide to in situ immune response analysis of lymphoid tissues by immunohistochemical methods. In: Weir DM, Blackwell L, Herzenberg L, Herzenberg L, editors. Weir's handbook of experimental immunology. Oxford: Blackwell Scientific Publications; 1998. p. 2041–2.
Claassen E, Gerritse K, Laman JD, Boersma WJ. New immunoenzyme-cytochemical stainings for the in situ detection of epitope specificity and isotype of antibody forming B cells in experimental and natural (auto) immune responses in animals and man. [Review]. J Immunol Methods 1992; 150: 207–16.[ISI][Medline]
Cortese I, Capone S, Luchetti S, Grimaldi LM, Nicosia A, Cortese R. CSF-enriched antibodies do not share specificities among MS patients. Mult Scler 1998; 4: 118–23.
de Vries HE, Kuiper J, de Boer AG, Van Berkel TJ, Breimer DD. The blood-brain barrier in neuroinflammatory diseases. [Review]. Pharmacol Rev 1997; 49: 143–55.
Ehl S, Hombach J, Aichele P, Rulicke T, Odermatt B, Hengartner H, et al. Viral and bacterial infections interfere with peripheral tolerance induction and activate CD8+ T cells to cause immunopathology. J Exp Med 1998; 187: 763–74.
Forestier C, Moreno E, Pizarro-Cerda J, Gorvel JP. Lysosomal accumulation and recycling of lipopolysaccharide to the cell surface of murine macrophages, an in vitro and in vivo study. J Immunol 1999; 162: 6784–91.
Gupta D, Wang Q, Vinson C, Dziarski R. Bacterial peptidoglycan induces CD14-dependent activation of transcription factors CREB/ATF and AP-1. J Biol Chem 1999; 274: 14012–20.
Hamann L, El-Samalouti V, Ulmer AJ, Flad HD, Rietschel ET. Components of gut bacteria as immunomodulators. [Review]. Int J Food Microbiol 1998; 41: 141–54.[ISI][Medline]
Hazenberg MP. Intestinal flora bacteria and arthritis: why the joint? Scand J Rheumatol Suppl 1995; 101: 207–11.[Medline]
Hazenberg MP, Pennock-Schroder AM, Wensinck F, Van de Merwe JP. Effect of a soluble bacterial carbohydrate fraction on the viscosity of intestinal contents in healthy subjects and patients with Crohn's disease. Eur J Clin Invest 1989; 19: 61–4.[ISI][Medline]
Hazenberg MP, de Visser H, Bras MJ, Prins ME, van de Merwe JP. Serum antibodies to peptidoglycan-polysaccharide complexes from the anaerobic intestinal flora in patients with Crohn's disease. Digestion 1990; 47: 172–80.[ISI][Medline]
Hoffmann JA, Kafatos FC, Janeway CA, Ezekowitz RA. Phylogenetic perspectives in innate immunity. [Review]. Science 1999; 284: 1313–18.
Hoijer MA, Melief MJ, Keck W, Hazenberg MP. Purification and characterization of N-acetylmuramyl-L-alanine amidase from human plasma using monoclonal antibodies. Biochim Biophys Acta 1996; 1289: 57–64.[Medline]
Hoijer MA, Melief MJ, Calafat J, Roos D, van den Beemd RW, van Dongen JJ, et al. Expression and intracellular localization of the human N-acetylmuramyl- L-alanine amidase, a bacterial cell wall-degrading enzyme. Blood 1997a; 90: 1246–54.
Hoijer MA, Melief MJ, Debets R, Hazenberg MP. Inflammatory properties of peptidoglycan are decreased after degradation by human N-acetylmuramyl-L-alanine amidase. Eur Cytokine Netw 1997b; 8: 375–81.[ISI][Medline]
Kool J, De Visser H, Gerrits-Boeye MY, Klasen IS, Melief MJ, Van Helden-Meeuwsen CG, et al. Detection of intestinal flora-derived bacterial antigen complexes in splenic macrophages of rats. J Histochem Cytochem 1994; 42: 1435–41.[Abstract]
Laman JD, Gerritse K, Fasbender M, Boersma WJ, van Rooijen N, Claassen E. Double immunocytochemical staining for in vivo detection of epitope specificity and isotype of antibody-forming cells against synthetic peptides homologous to human immunodeficiency virus-1. J Histochem Cytochem 1990; 38: 457–62.[Abstract]
Lassmann H. Pathology of multiple sclerosis. In: Compston A, Ebers G, Lassmann H, McDonald I, Matthews B, Wekerle H, editors. McAlpine's multiple sclerosis. 3rd ed. London: Churchill Livingstone; 1998. p. 323–58.
Lassmann H, Wekerle H. Experimental models of multiple sclerosis. In: Compston A, Ebers G, Lassmann H, McDonald I, Matthews B, Wekerle H, editors. McAlpine's multiple sclerosis. 3rd ed. London: Churchill Livingstone; 1998. p. 409–25.
Lassmann H, Raine CS, Antel J, Prineas JW. Immunopathology of multiple sclerosis: report on an international meeting held at the Institute of Neurology of the University of Vienna. J Neuroimmunol 1998; 86: 213–17.[ISI][Medline]
Le Roy D, Di Padova F, Tees R, Lengacher S, Landmann R, Glauser MP, et al. Monoclonal antibodies to murine lipopolysaccharide (LPS)-binding protein (LBP) protect mice from lethal endotoxemia by blocking either the binding of LPS to LBP or the presentation of LPS/LBP complexes to CD14. J Immunol 1999; 162: 7454–60.
Lehtonen L, Eerola E, Oksman P, Toivanen P. Muramic acid in peripheral blood leukocytes of healthy human subjects. J Infect Dis 1995; 171: 1060–4.[ISI][Medline]
Lehtonen L, Eerola E, Toivanen P. Muramic acid in human peripheral blood leucocytes in different age groups. Eur J Clin Invest 1997; 27: 791–2.[ISI][Medline]
Mattsson E, Van Dijk H, Van Kessel K, Verhoef J, Fleer A, Rollof J. Intracellular pathways involved in tumor necrosis factor-alpha release by human monocytes on stimulation with lipopolysaccharide or staphylococcal peptidoglycan are partly similar. J Infect Dis 1996; 173: 212–18.[ISI][Medline]
Matyszak MK. Inflammation in the CNS: balance between immunological privilege and immune responses. [Review]. Prog Neurobiol 1998; 56: 19–35.[ISI][Medline]
Medzhitov R, Preston-Hurlburt P, Janeway CA Jr. A human homologue of the Drosophila Toll protein signals activation of adaptive immunity. Nature 1997; 388: 394–7.[Medline]
Melief MJ, Hoijer MA, Van Paassen HC, Hazenberg MP. Presence of bacterial flora-derived antigen in synovial tissue macrophages and dendritic cells. Br J Rheumatol 1995; 34: 1112–6.
Mellman I, Turley SJ, Steinman RM. Antigen processing for amateurs and professionals. [Review]. Trends Cell Biol 1998; 8: 231–7.[ISI][Medline]
Noseworthy JH. Progress in determining the causes and treatment of multiple sclerosis. [Review]. Nature 1999; 399 (6738 Suppl): A40–7.[Medline]
Purba JS, Hofman MA, Portegies P, Troost D, Swaab DF. Decreased number of oxytocin neurons in the paraventricular nucleus of the human hypothalamus in AIDS. Brain 1993; 116: 795–809.
Randolph GJ, Beaulieu S, Lebecque S, Steinman RM, Muller WA. Differentiation of monocytes into dendritic cells in a model of transendothelial trafficking. Science 1998; 282: 480–3.
Ravid R, Swaab DF, van Zwieten EJ, Salehi A. Controls are what makes a brain bank go round. In: Cruz-Sanchez FF, Ravid R, Cuzner ML, editors. Neuropathological diagnostic criteria for brain banking, biomedical and health research, Vol. 10. Amsterdam: IOS Press; 1995. p. 4–13.
Relman DA. The search for unrecognized pathogens. Science 1999; 284: 1308–10.
Rescigno M, Granucci F, Citterio S, Foti M, Ricciardi-Castagnoli P. Coordinated events during bacteria-induced DC maturation. [Review]. Immunol Today 1999; 20: 200–3.[ISI][Medline]
Röcken M, Urban JF, Shevach EM. Infection breaks T-cell tolerance. Nature 1992; 359: 79–82.[Medline]
Schleifer KH, Kandler O. Peptidoglycan types of bacterial cell walls and their taxonomic implications. [Review]. Bacteriol Rev 1972; 36: 407–77.
Schrijver IA, Melief MJ, Eulderink F, Hazenberg MP, Laman JD. Bacterial peptidoglycan polysaccharides in sterile human spleen induce proinflammatory cytokine production by human blood cells. J Infect Dis 1999; 179: 1459–68.[ISI][Medline]
Schrijver IA, Melief MJ, van Meurs M, Companjen AR, Laman JD. Pararosaniline fixation for detection of co-stimulatory molecules, cytokines, and specific antibody. J Histochem Cytochem 2000; 48: 95–103.
Schrijver IA, Melief M-J, Markusse I, Van Aelst, Opdenakker G, Hazenberg MP et al. Peptidoglycan from sterile human spleen induces T cell proliferation and inflammatory mediators in rheumatoid arthritis patients and healthy subjects. Rheumatology 2001a; 40: 438–46.
Schrijver IA, de Man YA, Melief M-J, Van Laar JM, Markusse HM, Klasen IS et al. Reduced systemic IgG levels against peptidoglycan in rheumatoid arthritis (RA) patients. Clin Exp Immunol 2001b; 123: 140–6.[ISI][Medline]
Schwandner R, Dziarski R, Wesche H, Rothe M, Kirschning CJ. Peptidoglycan- and lipoteichoic acid-induced cell activation is mediated by toll-like receptor 2. J Biol Chem 1999; 274: 17406–9.
Segal BM, Klinman DM, Shevach EM. Microbial products induce autoimmune disease by an IL-12-dependent pathway. J Immunol 1997; 158: 5087–90.[Abstract]
Slootstra JW, Puijk WC, Ligtvoet GJ, Kuperus D, Schaaper WM, Meloen RH. Screening of a small set of random peptides: a new strategy to identify synthetic peptides that mimic epitopes. J Mol Recognit 1997; 10: 217–24.[ISI][Medline]
Soldan SS, Berti R, Salem N, Secchiero P, Flamand L, Calabresi PA, et al. Association of human herpes virus 6 (HHV-6) with multiple sclerosis: increased IgM response to HHV-6 early antigen and detection of serum HHV-6 DNA. Nat Med 1997; 3: 1394–7.[ISI][Medline]
Timmerman CP, Mattsson E, Martinez-Martinez L, De Graaf L, Van Strijp JA, Verbrugh HA, et al. Induction of release of tumor necrosis factor from human monocytes by staphylococci and staphylococcal peptidoglycans. Infect Immun 1993; 61: 4167–72.
Ulevitch RJ. Endotoxin opens the Tollgates to innate immunity [news]. Nat Med 1999; 5: 144–5.[ISI][Medline]
Vella AT, McCormack JE, Linsley PS, Kappler JW, Marrack P. Lipopolysaccharide interferes with the induction of peripheral T cell death. Immunity 1995; 2: 261–70.[ISI][Medline]
Vella A, Teague TK, Ihle J, Kappler J, Marrack P. Interleukin 4 (IL-4) or IL-7 prevents the death of resting T cells: stat6 is probably not required for the effect of IL-4. J Exp Med 1997; 186: 325–30.
Vella AT, Dow S, Potter TA, Kappler J, Marrack P. Cytokine-induced survival of activated T cells in vitro and in vivo. Proc Natl Acad Sci USA 1998; 95: 3810–5.
Weidemann B, Brade H, Rietschel ET, Dziarski R, Bazil V, Kusumoto S, et al. Soluble peptidoglycan-induced monokine production can be blocked by anti-CD14 monoclonal antibodies and by lipid A partial structures. Infect Immun 1994; 62: 4709–15.
Weidemann B, Schletter J, Dziarski R, Kusumoto S, Stelter F, Rietschel ET, et al. Specific binding of soluble peptidoglycan and muramyldipeptide to CD14 on human monocytes. Infect Immun 1997; 65: 858–64.[Abstract]
Received August 30, 2000. Revised February 20, 2001. Accepted March 20, 2001.
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