Development of a novel scoring system for identifying emerging chemical risks in the food chain.

The European Food Safety Authority (EFSA) is responsible for risk assessment of all aspects of food safety, including the establishment of procedures aimed at the identification of emerging risks to food safety. Here, a scoring system was developed for identifying chemicals registered under the European REACH Regulation that could be of potential concern in the food chain using the following parameters: (i) environmental release based on maximum aggregated tonnages and environmental release categories; (ii) biodegradation in the environment; (iii) bioaccumulation and in vivo and in vitro toxicity. The screening approach was tested on 100 data-rich chemicals registered under the REACH Regulation at aggregated volumes of at least 1000 tonnes per annum. The results show that substance-specific data generated under the REACH Regulation can be used to identify potential emerging risks in the food chain. After application of the screening procedure, priority chemicals can be identified as potentially emerging risk chemicals through the integration of exposure, environmental fate and toxicity. The default approach is to generate a single total score for each substance using a predefined weighting scenario. However, it is also possible to use a pivot table approach to combine the individual scores in different ways that reflect user-defined priorities, which enables a very flexible, iterative definition of screening criteria. Possible applications of the approaches are discussed using illustrative examples. Either approach can then be followed by in-depth evaluation of priority substances to ensure the identification of substances that present a real emerging chemical risk in the food chain.

Assessment of mechanisms driving non-linear dose-response relationships in genotoxicity testing.

In genetic toxicology, risk assessment has traditionally adopted linear dose-responses for any compound that causes genotoxic effects. Increasing evidence of non-linear dose-responses, however, suggests potential cellular tolerance to low levels of many genotoxicants with diverse modes of action. Such putative non-linear dose-responses need to be substantiated by strong mechanistic data that identifies the mechanisms responsible for the tolerance to low doses. This can be achieved by experimental demonstration of cytoprotective mechanisms and by providing experimental support for the existence of tolerance mechanisms against low dose effects. By highlighting key experiments into low dose mechanisms, this review aims to clarify which mechanistic data are required to support the use of non-linear dose-response models in risk assessment. Such key experiments are presented and discussed for alkylating agents, oxidants, particulate matter, nucleoside analogues, topoisomerase inhibitors and aneugens and exemplify the use of gene knockout models or transgenic models as well as chemical modulators of key effectors of relevant pathways and their impact on dose-response relationships. In vitro studies are particularly valuable to elucidate mechanisms of low-dose protection or lack thereof, while in vivo experiments are most appropriate for deriving a safe dose. In order to evaluate the existence of non-linear dose-response relationships for genotoxicants, we suggest that careful attention should be given to the mode of genotoxic action, relevant biomarkers of exposure, as well as to the existence and impact of potential cytoprotective mechanisms like detoxifying metabolism and DNA repair.

Evaluation of inhalation TTC values with the database RepDose.

The thresholds of toxicological concern (TTCs) define limit values for substances of unknown toxicity below which dietary intake is considered to be of no concern to human health. The TTC concept has already been used for risk assessment of e.g. food contaminants or flavoring substances and is in discussion to be applied to other classes of compounds such as cosmetic ingredients, household products, non-relevant metabolites in drinking water, and impurities in pharmaceuticals. The present publication aimed to evaluate whether the current TTC concept can also be applied to define limit values for inhalation exposure, using a data set of 203 industrial chemicals from the database RepDose. It has been shown, that the NOEC values in classes 1, 2, and 3 are distributed over six orders of magnitude resulting in a considerable overlap between the distribution curves for the three classes. Inhalation thresholds for Cramer classes 1 (compounds likely to be of low-toxicity), 2 (compounds likely to be of moderate toxicity), and 3 (compounds suspect for high toxicity) were analyzed close to the approach described by Munro for oral TTCs. The 5th percentiles NOEC of Cramer classes 1-3 result in thresholds of 1.5×10(-3) ppm for Cramer class 1 and 2.2×10(-5) ppm for Cramer class 3. A threshold could not be derived for class 2 because of the small number of compounds available. If calculated as body doses, the inhalation thresholds for classes 1 and 3 (71 and 4 µg/person/d, respectively) are considerably lower than the oral thresholds derived by Munro (1800 and 90 µg/person/d). It has been shown that one reason for this difference is the high sensitivity of the respiratory tract to local effects. In a next step, the values obtained were further refined. If organophosphates or compounds with structural alerts for genotoxicity are excluded, the TTC in Cramer class 1 increases, whereas the TTC in Cramer class 3 remains the same. Based on these analyses two inhalation TTCs for non-genotoxic compounds are proposed: 3.6×10(-3) ppm (180 µg/person/d) for Cramer class 1 and 2.4×10(-5)ppm (4 µg/person/d) for Cramer class 3.

MxA protein--an interferon beta biomarker in primary progressive multiple sclerosis patients.

BACKGROUND AND PURPOSE: Interferon beta (IFNbeta) preparations have some effect on the progressive phase of multiple sclerosis (MS). This limited effect might be partially because of a certain number of IFNbeta non-responders. Myxovirus resistance protein A (MxA)--a marker of IFNbeta bioactivity--was correlated with the clinical response during an uncontrolled trial, investigating the safety of IFNbeta-1b in primary progressive (PPMS) patients. METHODS: Twenty PPMS were treated with IFNbeta-1b (s.c.) for 1 year. Blood samples were taken before and 1, 2, 3, 6, 9, 12, and 15 months after treatment initiation and MxA protein levels were measured. Patients were clinically evaluated by EDSS and the more sensitive Incapacity Status Scale (ISS) and stratified in a stable and a progressing group. RESULTS: Using ISS criteria, 11 patients remained stable and nine patients progressed during treatment. The mean area under the curve of log MxA levels during treatment were significantly higher in stable than in progressing patients (10.87 vs. 5.99; P = 0.002). CONCLUSION: A good biological response to IFNbeta might be associated with a better clinical effect of this drug and could be helpful in future clinical studies for early identification of treatment responders.

Interferon-beta1b treatment modulates cytokines in patients with primary progressive multiple sclerosis.

OBJECTIVES: It is unknown whether the immunological effects of beta-interferon (IFN-beta) differ in primary progressive multiple sclerosis (PPMS) when compared with relapsing-remitting multiple sclerosis (RRMS). Therefore, we investigated the effects of IFN-beta1b treatment in PPMS on proliferation and cytokine pattern of peripheral blood mononuclear cells (PBMC) and interleukin-10 (IL-10) serum level. METHODS: Eighteen patients were treated with IFN-beta1b for 12 months in an open-label trial. Serum and PBMC were collected longitudinally. RESULTS: Interleukin-10 serum levels increased (P = 0.02) during treatment. Tumor necrosis factor-alpha was increased in anti CD3 (OKT3) antibody stimulated PBMC during treatment (P = 0.04), whereas secretion of IL-10 was decreased in OKT3 (P = 0.04), but increased in concavalin A stimulated PBMC (P = 0.02). CONCLUSIONS: Interleukin-10 serum levels rose in IFN-beta1b-treated patients as has been observed in RRMS. The changes in cytokine patterns secreted by T-lymphocytes of PPMS patients, however, differ from effects observed in RRMS supporting the hypothesis that PPMS differs in some immunological aspects from RRMS.

REPDOSE: A database on repeated dose toxicity studies of commercial chemicals--A multifunctional tool.

A database for repeated dose toxicity data has been developed. Studies were selected by data quality. Review documents or risk assessments were used to get a pre-screened selection of available valid data. The structure of the chemicals should be rather simple for well defined chemical categories. The database consists of three core data sets for each chemical: (1) structural features and physico-chemical data, (2) data on study design, (3) study results. To allow consistent queries, a high degree of standardization categories and glossaries were developed for relevant parameters. At present, the database consists of 364 chemicals investigated in 1018 studies which resulted in a total of 6002 specific effects. Standard queries have been developed, which allow analyzing the influence of structural features or PC data on LOELs, target organs and effects. Furthermore, it can be used as an expert system. First queries have shown that the database is a very valuable tool.

Clinical course, pathological correlations, and outcome of biopsy proved inflammatory demyelinating disease.

BACKGROUND: A pathological classification has been developed of early active multiple sclerosis (MS) lesions that reveals four patterns of tissue injury: I-T cell/macrophage associated; II-antibody/complement associated; III-distal oligodendrogliopathy, and IV-oligodendrocyte degeneration in the periplaque white matter. Mechanisms of demyelination in early MS may differ among the subgroups. Previous studies on biopsied MS have lacked clinicopathological correlation and follow up. Critics argue that observations are not generalisable to prototypic MS. OBJECTIVE: To describe the clinicopathological characteristics of the MS Lesion Project biopsy cohort. METHODS: Clinical characteristics and disability of patients with pathologically confirmed inflammatory demyelinating disease (excluding ADEM) classified immunopathologically (n = 91) and patients from the Olmsted County MS prevalence cohort (n = 218) were determined. RESULTS: Most patients who underwent biopsy and had pathologically proved demyelinating disease ultimately developed definite (n = 70) or probable (n = 12) MS (median follow up 4.4 years). Most had a relapsing remitting course and 73% were ambulatory (EDSS < or =4) at last follow up. Nine patients remained classified as having an isolated demyelinating syndrome at last follow up. Patients with different immunopathological patterns had similar clinical characteristics. Although presenting symptoms and sex ratios differed, the clinical course in biopsy patients was similar to the prevalence cohort. Median EDSS was <4.0 in both cohorts when matched for disease duration, sex, and age. CONCLUSIONS: Most patients undergoing biopsy, who had pathologically confirmed demyelinating disease, were likely to develop MS and remain ambulatory after a median disease duration of 4.4 years. The immunopathological patterns lacked specific clinical correlations and were not related to the timing of the biopsy. These data suggest that pathogenic implications derived largely from MS biopsy studies may be extrapolated to the general MS population.

Mutagenicity testing with transgenic mice. Part I: Comparison with the mouse bone marrow micronucleus test.

As part of a larger literature study on transgenic animals in mutagenicity testing, test results from the transgenic mutagenicity assays (lacI model; commercially available as the Big Blue(R) mouse, and the lacZ model; commercially available as the Mutatrade markMouse), were compared with the results on the same substances in the more traditional mouse bone marrow micronucleus test. 39 substances were found which had been tested in the micronucleus assay and in the above transgenic mouse systems. Although, the transgenic animal mutation assay is not directly comparable with the micronucleus test, because different genetic endpoints are examined: chromosome aberration versus gene mutation, the results for the majority of substances were in agreement. Both test systems, the transgenic mouse assay and the mouse bone marrow micronucleus test, have advantages and they complement each other. However, the transgenic animal assay has some distinct advantages over the micronucleus test: it is not restricted to one target organ and detects systemic as well as local mutagenic effects.

Interferon beta-1b modulates serum sVCAM-1 levels in primary progressive multiple sclerosis.

Endothelial activation is a key feature of multiple sclerosis (MS) pathogenesis. It is modulated by interferon beta-1b (IFNB-1b) treatment in relapsing-remitting MS (RRMS) patients. This particular pharmacodynamic effect still has to be proven in primary progressive MS (PPMS). In the current study, serum concentrations of soluble vascular cell adhesion molecule-1 (sVCAM-1) and sE-selectin were analyzed longitudinally in 18 PPMS patients before, during and after 12 months of treatment with IFNB-1b. During drug therapy there was a significant early and sustained increase of sVCAM-1 (overall P < 0.0001). Flu-like symptoms induced by IFNB-1b and also concomitant infections were associated with higher sVCAM-1 levels. Neutralizing antibodies to IFNB-1b were associated with lower sVCAM-1 levels. In conclusion, IFNB-1b modulates the adhesion cascade in patients with PPMS in a similar way it does in RRMS. Nevertheless, a clinical effect of IFNB in PPMS still has to be proven in a randomized controlled clinical trial.

The macrophage activity marker sCD14 is increased in patients with multiple sclerosis and upregulated by interferon beta-1b.

The soluble form of the CD14 molecule (sCD14), a macrophage activity marker, was measured in the plasma of 17 patients with primary progressive multiple sclerosis (PPMS) and 20 patients with relapsing remitting MS (RRMS). In patients with PPMS, sCD14 levels were determined before and after treatment with interferon beta (IFNB). In both PPMS and in RRMS, sCD14 levels were significantly elevated compared to healthy controls. In patients with PPMS, sCD14 levels increased significantly during the first 3 months of IFNB therapy, then slightly decreased, but still remained elevated compared with levels before therapy. Therefore, the elevated sCD14 levels may be a marker in evaluating biological response to IFNB therapy.

Effects of low-dose, noncytotoxic, intraarticular liposomal clodronate on development of erosions and proteoglycan loss in established antigen-induced arthritis in rabbits.

OBJECTIVE: To assess the clinical and histologic effects of an intraarticular application of low-dose (non-cytotoxic) liposomal clodronate in established antigen-induced monarthritis (AIA) in rabbits. METHODS: AIA was monitored by assessments of joint swelling, C-reactive protein levels, and radiographic changes in 17 NZW rabbits for 8 weeks during the course of weekly intraarticular injections of liposomal clodronate (0.145 mg/injection, low dose) or "empty" liposomes. The contralateral knee was injected with liposome buffer alone as the control. End-point analyses included macroscopic joint examination, immuno- and TUNEL staining, Safranin O staining/microspectrophotometry, and tumor necrosis factor alpha (TNFalpha) convertase enzyme (TACE) inhibition assay. RESULTS: Liposomal clodronate-treated rabbits showed a reduction and delay in joint swelling during the first 3 injections. Expression of matrix-bound (solubilized) TNFalpha, lining cell hyperplasia, and levels of RAM-11+ macrophages were low in the synovium of the liposomal clodronate treatment group, but the proportion of apoptotic lining cells was not affected. The radiologic score was low at the end of weeks 2 and 4, but at 8 weeks, no difference, compared with controls, was found in pannus formation or in the extent of joint erosion; also, joint swelling was higher than before initiation of treatment. Injections of liposomal clodronate prevented cartilage proteoglycan loss, which was significant in the superficial zone only. TACE activity was not inhibited by clodronate. CONCLUSION: Liposomal clodronate had temporary antiinflammatory and antierosive effects on established AIA in rabbits. Over the long-term, the loss of cartilage proteoglycans was halted. This observed treatment effect may be related to the inhibition of TNFalpha production and processing in the synovium.

A longitudinal MRI study of histopathologically defined hypointense multiple sclerosis lesions.

Severe tissue destruction is the presumed histopathological correlate of hypointense multiple sclerosis (MS) lesions. In this study we correlated changes of lesion hypointensity over time with initial histopathological features in 14 biopsied MS lesions. The extent of hypointensity increased in initially demyelinated plaques and decreased in remyelinating lesions. The initial axonal loss determined the increase of hypointensity over time. In conclusion, both axonal loss and demyelinating activity determine the evolution of hypointensity over time.

Macrophages are eliminated from the injured peripheral nerve via local apoptosis and circulation to regional lymph nodes and the spleen.

The present study investigated the fate of macrophages in peripheral nerves undergoing Wallerian degeneration, especially their disappearance from the injured nerves after phagocytosis of axonal and myelin debris. Wallerian degeneration was induced in adult male C57Bl/6 mice by transecting the right sciatic nerve. Five days after transection, the male sciatic nerves were transplanted into female recipient mice by placing them exactly parallel to the host sciatic nerves. Nerves of the female recipient mice were also transected to induce breakdown of the blood-nerve barrier in the host animal. Apoptosis was assessed by morphological, immunohistochemical (activated caspase-3), and molecular (DNA fragmentation) methods in transplanted, recipient, and in control nerves. A subpopulation of macrophages within the degenerating nerves died locally by apoptosis in each experiment. The fate of the male macrophages within the transplanted nerves and the host organism was investigated by in situ hybridization with a Y-chromosome-specific DNA probe (145SC5). In situ hybridization specifically stained cells within the transplanted male nerve. Y-chromosome-positive cells were detected not only inside the transplanted nerve, but also inside the female host nerve, the perineurial tissue, the local perineurial blood vessels, draining lymph nodes and the spleen of the female host, suggesting hematogenous as well as lymphatic elimination of macrophages from the injured nerve. These data indicate that local apoptosis and systemic elimination via circulation to the local lymph nodes and the spleen are involved in the disappearance of macrophages from the injured peripheral nervous system.

Analysis of interleukin-4 receptor alpha chain variants in multiple sclerosis.

A recent candidate gene study employing microsatellite markers suggested a possible linkage of multiple sclerosis (MS) with the interleukin-4 receptor (IL4R) gene. Consequently, we investigated the association of different IL4R variants with MS in 341 German MS patients and 305 healthy controls. Analysis of the first 100 MS patients for six IL4R variants showed an increased frequency of the R551 variant in MS patients versus healthy controls and carriage of the same IL4R variant was weakly associated with myelin oligodendrocyte glycoprotein (MOG) autoantibody production. However, further analysis of all 341 MS patients did not confirm the finding that this IL4R variant represents a general genetic risk factor for MS but revealed an increased frequency of the R551 variant in MS patients with primary progressive MS (PPMS, n=48) as compared to patients with relapsing remitting MS or secondary progressive MS (RR/SPMS n=284; P=0.005 for genotype differences) and to 305 healthy controls (P=0.001 for genotype differences). This association was statistically independent of the presence of the well-known MS susceptibility allele HLA-DRB1*15. After correction for multiple comparisons only the genotype differences between PPMS patients and healthy controls remained statistically significant. These results indicate, that the IL4R variant R551 may influence the genetic predisposition for PPMS but does not represent a general genetic risk factor for MS.

Acute axonal injury in multiple sclerosis. Correlation with demyelination and inflammation.

Damage to axons is taken as a key factor of disability in multiple sclerosis, but its pathogenesis is largely unknown. Axonal injury is believed to occur as a consequence of demyelination and was recently shown to be a feature even of the early disease stages. The present study was aimed at characterizing the association of axonal injury and histopathological hallmarks of multiple sclerosis such as demyelination, cellular infiltration and expression of inflammatory mediators. Therefore, axon reduction and signs of acute axonal damage were quantified in early lesion development of chronic multiple sclerosis and correlated with demyelinating activity and inflammation. Patients with secondary progressive multiple sclerosis revealed the most pronounced axonal injury, whereas primary progressive multiple sclerosis patients surprisingly showed relatively little acute axonal injury. Acute axonal damage, as defined by the accumulation of amyloid precursor protein (APP), was found to occur not only in active demyelinating but also in remyelinating and inactive demyelinated lesions with a large inter-individual variability. Only few remyelinating lesions were adjacent to areas of active demyelination. In this minority of lesions, axonal damage may have originated from the neighbourhood. APP expression in damaged axons correlated with the number of macrophages and CD8-positive T lymphocytes within the lesions, but not with the expression of tumour necrosis factor-alpha (TNF-alpha) or inducible nitric oxide synthase (iNOS). Axonal injury is therefore, at least in part, independent of demyelinating activity, and its pathogenesis may be different from demyelination. This has major implications for therapeutic strategies, which aim at preventing both demyelination and axonal loss.

Dose response of early effects related to tumor promotion of 2-acetylaminofluorene.

The genotoxic effects of 2-acetylaminofluorene (AAF) alone cannot explain the formation of rat liver tumors. It has been proposed that mitochondrial effects are associated with its tumor-promoting properties. These mitochondrial effects are thought to trigger apoptosis and regenerative proliferation, which alters the liver lobule in a cirrhosis-like manner. A situation is generated which favors the growth of initiated cells. To test this sequence of events, the dose dependence of early effects with time was studied. Male Wistar rats received 50, 100, 200, 400, or 800 ppm AAF in the diet and the following endpoints were analyzed at 2, 4, 8, and 16 weeks of feeding: apoptotic cell death, cell proliferation, GST-P-positive foci (placental form of glutathione S-transferase), and morphological alterations. Hydrolyzable hemoglobin adducts were used as a dosimeter for metabolic activation after 2 weeks of feeding. The hemoglobin adduct levels increased linearly with dose. With the conventional carcinogenic concentration of 200-ppm AAF in the diet, the number of apoptoses increased first, predominantly in the periportal area (2 weeks). Cell proliferation followed with some delay (4 weeks). This reflects regenerative tissue response and not the growth of initiated cells, because the number of enzyme-altered foci was still extremely low at that time. Foci developed only later when the morphology had changed. With 50 ppm AAF in the diet, a no-effect level had not been reached for any of the endpoints, but foci developed much more gradually than with higher doses. Unexpectedly, the proliferative response stabilized at 8 weeks with a labeling index of 12-17, with all AAF concentrations. The observed sequence of events supports the hypothesis. It is concluded that (1) The proliferation of initiated cells-defined as promotable cells-is largely determined by the cellular environment, such as morphologically altered liver. (2) The morphological alterations in rat liver result from imperfect regeneration from toxic effects. (3) Imperfect regeneration results from limitations in the possibilities to adapt to chemical stress. (4) If these limits are overwhelmed and morphology has changed to a certain extent, preneoplastic foci develop; this occurs much faster, at least, than without these changes.

Tumour necrosis factor alpha mRNA expression in early multiple sclerosis lesions: correlation with demyelinating activity and oligodendrocyte pathology.

The precise role of tumour necrosis factor alpha (TNFalpha) in multiple sclerosis (MS) is still controversial. Most findings from the animal model experimental allergic encephalomyelitis have yet to be confirmed in multiple sclerosis. The aim of this study was to define the significance of TNFalpha with respect to the hallmark of MS, that is demyelination. Therefore, 78 lesion areas from diagnostic brain biopsies of 32 patients were analysed. Lesion demyelinating activity was classified by the presence of myelin degradation products in macrophages and macrophage activation markers. Non-radioactive in situ hybridisation was carried out to detect TNFalpha mRNA expressing cells. DNA fragmentation was visualised by TdT-mediated X-dUTP nick end labeling. A significantly higher number of cells expressed TNFalpha mRNA in active demyelinating lesions than in inactive or remyelinating lesions irrespective of the extent of the inflammatory infiltrate. TNFalpha mRNA expression correlated with the appearance of DNA fragmentation in T lymphocytes and oligodendrocytes within the lesions. In the periplaque white matter, expression of TNFalpha mRNA negatively correlated with oligodendrocyte numbers. These data support previous findings from animal models and in vitro experiments. Although not proving, the current study strongly suggests a pathogenic role of TNFalpha in demyelination in human multiple sclerosis and gives further support for TNFalpha-directed therapeutic strategies.

Inflammatory CNS demyelination: histopathologic correlation with in vivo quantitative proton MR spectroscopy.

BACKGROUND AND PURPOSE: The mechanisms behind the demyelination that is characteristic of multiple sclerosis (MS) are still poorly understood. The purpose of this study was to compare immunopathologic findings in demyelinating lesions of three patients with in vivo assessments obtained by quantitative proton MR spectroscopy (MRS). METHODS: Between four and seven stereotactic needle brain biopsies were performed in three young adults with diagnostically equivocal findings for MS. Axonal density, gliosis, blood brain-barrier breakdown, and demyelinating activity of lesions were determined. Combined MR/MRS studies were performed (T1-weighted fast low-angle shot and single-voxel stimulated-echo acquisition mode), and absolute metabolite levels were obtained with a user-independent fitting routine. Metabolite control values were obtained from a group of age-matched healthy volunteers (n = 40, age range, 20-25 years old). Alterations of metabolite levels of control subjects were considered significant when exceeding two standard deviations. RESULTS: There were parallel decreases of N-acetylaspartate (21%-82%) and reductions of axonal density (44%-74%) in demyelinating plaques. Concomitant increases of choline (75%-152%) and myo-inositol (84%-160%) corresponded to glial proliferation. Elevated lactate was associated with inflammation. CONCLUSION: The present data suggest that in vivo MRS indicates key pathologic features of demyelinating lesions.

Bcl-2-expressing oligodendrocytes in multiple sclerosis lesions.

Multiple sclerosis (MS) is a chronic inflammatory disease of the central nervous system leading to selective destruction of myelin sheaths and/or oligodendrocytes. The immunological mechanisms responsible for myelin destruction and the primary target of the immune response have not yet been identified. Prior studies have reported a variable degree of oligodendrocyte preservation in actively demyelinating lesions. We have previously demonstrated that oligodendrocyte survival is heterogenous and varies between individual MS patients. Bcl-2 belongs to the group of apoptosis-associated proteins that protects cells from cell death. The purpose of the present study was to determine whether bcl-2 expression is associated with oligodendrocyte preservation observed in some early MS lesions. Double immunocytochemistry was performed with antibodies against bcl-2 and myelin oligodendrocyte glycoprotein (MOG) to identify bcl-2-expressing oligodendrocytes within MS lesions from 43 patients. The number of bcl-2-positive oligodendrocytes was determined depending on the lesion demyelinating activity and the disease course of the patients. The number of bcl-2-expressing oligodendrocytes increased within demyelinating lesions compared to the periplaque white matter, with highest numbers in remyelinating lesions. There was a significant association between the presence of bcl-2-positive oligodendrocytes and the presence of remyelination. The highest proportion of bcl-2-positive oligodendrocytes was observed in a subgroup of patients with relapsing-remitting disease course. The expression of apoptosis-associated proteins may contribute to oligodendrocyte preservation or loss in MS lesions.