Comparison of T8+ cell-mediated suppressor and cytotoxic functions in multiple sclerosis

Innate, innate-like and adaptive lymphocytes in the pathogenesis of MS and EAE

Multiple sclerosis (MS) is a chronic inflammatory disease of the central nervous system (CNS) in which the immune system damages the protective insulation surrounding the nerve fibers that project from neurons. A hallmark of MS and its animal model, experimental autoimmune encephalomyelitis (EAE), is autoimmunity against proteins of the myelin sheath. Most studies in this field have focused on the roles of CD4⁺ T lymphocytes, which form part of the adaptive immune system as both mediators and regulators in disease pathogenesis. Consequently, the treatments for MS often target the inflammatory CD4⁺ T-cell responses. However, many other lymphocyte subsets contribute to the pathophysiology of MS and EAE, and these subsets include CD8⁺ T cells and B cells of the adaptive immune system, lymphocytes of the innate immune system such as natural killer cells, and subsets of innate-like T and B lymphocytes such as γδ T cells, natural killer T cells, and mucosal-associated invariant T cells. Several of these lymphocyte subsets can act as mediators of CNS inflammation, whereas others exhibit immunoregulatory functions in disease. Importantly, the efficacy of some MS treatments might be mediated in part by effects on lymphocytes other than CD4⁺ T cells. Here we review the contributions of distinct subsets of lymphocytes on the pathogenesis of MS and EAE, with an emphasis on lymphocytes other than CD4⁺ T cells. A better understanding of the distinct lymphocyte subsets that contribute to the pathophysiology of MS and its experimental models will inform the development of novel therapeutic approaches.

CD8(+) T-Cells as Immune Regulators of Multiple Sclerosis

The vast majority of studies regarding the immune basis of MS (and its animal model, EAE) have largely focused on CD4(+) T-cells as mediators and regulators of disease. Interestingly, CD8(+) T-cells represent the predominant T-cell population in human MS lesions and are oligoclonally expanded at the site of pathology. However, their role in the autoimmune pathologic process has been both understudied and controversial. Several animal models and MS patient studies support a pathogenic role for CNS-specific CD8(+) T-cells, whereas we and others have demonstrated a regulatory role for these cells in disease. In this review, we describe studies that have investigated the role of CD8(+) T-cells in MS and EAE, presenting evidence for both pathogenic and regulatory functions. In our studies, we have shown that cytotoxic/suppressor CD8(+) T-cells are CNS antigen-specific, MHC class I-restricted, IFNγ- and perforin-dependent, and are able to inhibit disease. The clinical relevance for CD8(+) T-cell suppressive function is best described by a lack of their function during MS relapse, and importantly, restoration of their suppressive function during quiescence. Furthermore, CD8(+) T-cells with immunosuppressive functions can be therapeutically induced in MS patients by glatiramer acetate (GA) treatment. Unlike CNS-specific CD8(+) T-cells, these immunosuppressive GA-induced CD8(+) T-cells appear to be HLA-E restricted. These studies have provided greater fundamental insight into the role of autoreactive as well as therapeutically induced CD8(+) T-cells in disease amelioration. The clinical implications for these findings are immense and we propose that this natural process can be harnessed toward the development of an effective immunotherapeutic strategy.

Mycophenolate mofetil improves neurological function and alters blood T-lymphocyte subsets in rats with experimental autoimmune encephalomyelitis

Objective

This study evaluated the clinical and pathological effects of the immunosuppressive agent mycophenolate mofetil (MMF) in rats with experimental autoimmune encephalomyelitis (EAE; a model of multiple sclerosis [MS]).

Methods

EAE rats were randomly divided into 4 groups: model alone ( n = 7); low- or high-dose MMF (20 and 30 mg/kg per day, respectively, n = 6 each) orally for 14 days; methylprednisolone (20 mg/kg per day, n = 6) injected once daily for 3 days. Six normal Wistar rats served as controls. Clinical signs and histopathological findings were evaluated 14 days after treatment started.

Results

Oral administration of high-dose MMF significantly ameliorated the course of EAE in rats: cumulative clinical scores were lower and weight loss was less than in rats receiving methylprednisolone. The ameliorated disease course was associated with alleviation of histopathological signs of EAE. Treatment increased the blood proportion of CD8+, CD4+CD25+ and CD4+CD45RA+ T cells, with a concomitant reduced proportion of CD4+ T cells and ratio of CD4+ to CD8+ T cells, compared with EAE model alone rats.

Conclusions

MMF may have pharmacological potential in MS treatment and these findings may help in understanding the pathophysiological mechanism of MS.

The sad plight of multiple sclerosis research (low on fact, high on fiction): critical data to support it being a neurocristopathy

The literature for evidence of autoimmunity in multiple sclerosis (MS) is analysed critically. In contrast to the accepted theory, the human counterpart of the animal model experimental autoimmune demyelinating disease, experimental allergic encephalomyelitis (EAE), is not MS but a different demyelinating disorder, i.e. acute disseminated encephalomyelitis and acute haemorrhagic leucoencephalitis. Extrapolation of EAE research to MS has been guided largely by faith and a blind acceptance rather than sound, scientific rationale. No specific or sensitive immunological test exists that is diagnostic of MS despite the extensive application of modern technology. Immunosuppression has failed to have any consistent effect on prognosis or disease progression. The available data on MS immunotherapy are conflicting, at times contradictory and are based on findings in animals with EAE. They show predominantly a 30% effect in relapsing/remitting MS which suggests powerful placebo effect. Critical analysis of the epidemiological data shows no association with any specific autoimmune diseases, but does suggest that geographic factors and age at development posit an early onset possibly dependent on environmental influences. Certain neurological diseases are, however, found in association with MS, namely hypertrophic peripheral neuropathy, neurofibromatosis-1, cerebral glioma, glioblastoma multiforme and certain familial forms of narcolepsy. These share a common genetic influence possibly from genes on chromosome 17 affecting cell proliferation. A significant number of these disorders are of neural crest origin, the classical example being abnormalities of the Schwann cell. These and other data allow us to propose that MS is a developmental neural crest disorder, i.e. a cristopathy, implicating glial cell dysfunction with diffuse blood-brain barrier breakdown. The data on transcription factor SOX10 mutations in animals may explain these bizarre clinical associations with MS and the phenotypic variability of such alterations (Cossais et al. 2010). Research directed to the area of neural crest associations is likely to be rewarding.

Autoreactive CD8+ T cells in multiple sclerosis: a new target for therapy?

Multiple sclerosis afflicts more than 1 million individuals worldwide and is widely considered to be an autoimmune disease. Traditionally, CD4(+) T helper cells have almost exclusively been held responsible for its immunopathogenesis, partly because certain MHC class II alleles clearly predispose for developing multiple sclerosis and also, because of their importance in inducing experimental autoimmune encephalomyelitis (EAE), the animal model for multiple sclerosis. However, several strategies that target CD4(+) T cells beneficially in EAE have failed to ameliorate disease activity in multiple sclerosis, and some have even triggered exacerbations. Recently, the potential importance of CD8(+) T cells has begun to emerge. Physiologically, CD8(+) T cells are essential for detecting and eliminating abnormal cells, whether infected or neoplastic. In multiple sclerosis, genetic associations with MHC class I alleles have now been established, and CD8(+) as well as CD4(+) T cells have been found to invade and clonally expand in inflammatory central nervous system plaques. Recent animal models induced by CD8(+) T cells show interesting similarities to multiple sclerosis, in particular, in lesion distribution (more inflammation in the brain relative to the spinal cord), although not all of the features of the human disease are recapitulated. Here we outline the arguments for a possible role for CD8(+) T cells, a lymphocyte subset that has long been underrated in multiple sclerosis and should now be considered in new therapeutic approaches.

TCR peptide therapy in human autoimmune diseases

Inflammatory Th1 cells reacting to tissue/myelin derived antigens likely contribute to the pathogenesis of diseases such as multiple sclerosis (MS), rheumatoid arthritis (RA), and psoriasis. One regulatory mechanism that may be useful for treating autoimmune diseases involves an innate second set of Th2 cells specific for portions of the T cell receptor of clonally expanded pathogenic Th1 cells. These Th2 cells are programmed to respond to internally modified V region peptides from the T cell receptor (TCR) that are expressed on the Th1 cell surface in association with major histocompatibility molecules. Once the regulatory Th2 cells are specifically activated, they may inhibit inflammatory Th1 cells through a non-specific bystander mechanism. A variety of strategies have been used by us to identify candidate disease-associated TCR V genes present on pathogenic Th1 cells, including BV5S2, BV6S5, and BV13SI in MS, BV3, BV14, and BV17 in RA, and BV3 and BV13S1 in psoriasis. TCR peptides corresponding to the mid region of these BV genes were found to be consistently immunogenic in vivo when administered either i.d. in saline or i.m. in incomplete Freund's adjuvant (IFA). In MS patients, repeated injection of low doses of peptides (100-300 microg) significantly boosted the number of TCR-reactive Th2 cells. These activated cells secreted cytokines, including IL-10, that are known to inhibit inflammatory Th1 cells. Cytokine release could also be induced in TCR-reactive Th2 cells by direct cell-cell contact with Th1 cells expressing the target V gene. These findings indicate the potential of regulatory Th2 cells to inhibit not only the target Th1 cells, but also bystander Th1 cells expressing different V genes specific for other autoantigens. TCR peptide vaccines have been used in our studies to treat a total of 171 MS patients (6 trials), 484 RA patients (7 trials), and 177 psoriasis patients (2 trials). Based on this experience in 824 patients with autoimmune diseases, TCR peptide vaccination is safe and well tolerated, and can produce significant clinical improvement in a subset of patients that respond to immunization. TCR peptide vaccination represents a promising approach that is well-suited for treating complex autoimmune diseases.

Evidence for a missed signal to the CD8+ cells in CSF of multiple sclerosis patients

Peripheral blood (PB) and cerebrospinal fluid (CSF) lymphocyte subpopulations, defined by various T-cell specific monoclonal antibodies and flow cytometry, were analysed in 44 relapsing remitting multiple sclerosis (RRMS) patients (including 21 subjects in the acute phase and 23 in the stable phase), 40 chronic-progressive multiple sclerosis (CPMS) patients, and 24 patients with other neurological diseases (OND), in order to verify the presence of any abnormality in the lymphocyte subset pattern. A significant increase in the total number of T-lymphocytes and the CD4+ subpopulation was found in the PB of the MS patients in comparison with the OND group. Moreover, a not statistically significant increase in CD4+ cells was observed in the CSF of MS patients. A statistically significant increase was also found in the CD4+ Leu 8+ (suppressor inducer) cells in the CSF of all of the MS groups. Finally, the CD8+ (suppressor/cytotoxic) cell levels, were significantly lower in the CSF of CPMS and stable RMS patients than in the CSF of the OND patients. As a whole, our data suggest that the immunosuppressive deficit that seems to be a constant finding in MS is not due to a decrease in suppressor inducer cell levels, as previously suggested, but may be caused by a missed or altered signal from the suppressor inducer to CD8+ suppressor cells.

Multiple sclerosis: immune mechanism and update on current therapies

Multiple sclerosis (MS) is a demyelinating disease of the central nervous system (CNS) afflicting approximately 250,000 individuals in the United States. This inflammatory disease has variable clinical manifestations, ranging from a relapsing-remitting course to a chronic progressive disease. Approximately one third of MS patients have chronic progressive disease often leading to severe impairment of mobility, paralysis, poor vision, and disturbances of bladder and bowel function. Although the etiology and pathogenesis remain unknown, accumulating evidence supports the hypothesis that exposure to an as-yet-unidentified infectious agent(s) triggers an aberrant immune response against self nervous tissue in genetically susceptible individuals. The tenfold higher concordance rate for MS in monozygotic twins compared to dizygotic twins, the increased incidence of MS in women compared to men (2:1), and the familial and racial occurrence of MS provide strong evidence that genetic factors influence susceptibility to MS. The major predisposing genes in MS are the human leukocyte antigen (HLA) class II molecules, DR15 and DQw6, molecularly defined as HLA-DRB1, 1501-DQA1 0102-DQB1 0602. In certain ethnic groups, MS susceptibility is more strongly associated with other DR molecules. Environmental factors are also believed to play a role, as suggested by the unique worldwide prevalence, migration effects, and epidemiological studies. Increased serum and cerebrospinal fluid antibody titers to numerous viruses have been reported; however, there have been no confirmed studies detecting viral RNA or antigen in MS brain tissue. At the present time, no known treatment can significantly alter the progression of MS. Based on the postulate that MS is an autoimmune disease associated with abnormalities in immunoregulation, a number of different immunosuppressive and immunomodulating agents have been tested as therapeutic modalities. In this article, we review the circumstantial evidence suggesting that immune system abnormalities are associated with the disease process, and provide an update on current therapies used in MS.

Phenotypic and functional characteristics of activated CD8+ cells: a CD11b-CD28- subset mediates noncytolytic functional suppression

Freshly isolated human CD8+ cells can be divided into mutually exclusive subsets bearing the phenotypes CD11b+(CD28-) or CD28+(CD11b-). We found that activation of CD8+ cells with anti-CD3 mAb and IL-2 preferentially expanded the CD11b-(CD28+) subset. This subset, when separated and activated independently, mediated both functional suppression and lectin-dependent cell cytotoxicity (LDCC). CD28- cells, prepared by elimination of the CD 28+ cells from expanded unfractionated CD8+ cell cultures, retained functional suppressor activity but demonstrated reduced LDCC compared to either the CD28+(CD11b-)-enriched fraction or the unfractionated CD8+ population. The majority of the CD28- cells were also CD11b-, reflecting the observation that initially CD11b+ cells lose CD11b expression following activation with anti-CD3 mAb and IL-2. Our results therefore indicate that CD8+ cells deriving from the CD11b+CD28- subset, but expressing neither CD11b nor CD28 after activation, represent the main noncytotoxic functional suppressor cell in the mitogen "activated" suppressor assay. The preferential expansion of CD8+CD28+ cells relative to CD8+CD28- cells, if occurring in vivo in the central nervous system (CNS) compartment, would be consistent with observed phenotypic analysis of cerebrospinal fluid-derived T cells and might contribute to the reduced functional suppressor activity previously found for CNS compared to peripheral blood-derived lymphocytes.

Sympathetic skin responses are decreased and lymphocyte beta-adrenergic receptors are increased in progressive multiple sclerosis

Immune abnormalities, including deficient CD8 lymphocyte-mediated suppression, have been implicated in the progression of multiple sclerosis (MS). The peripheral sympathetic branch of the autonomic nervous system innervates the lymphoid organs and affects immune function. Animals with an ablated sympathetic nervous system develop more severe experimental allergic encephalomyelitis than control animals and exhibit an increased density of beta-adrenergic receptors on their lymphocytes. Experimental allergic encephalomyelitis shares many features with MS. Accordingly, we investigated the psychogalvanic skin reflex in patients with rapidly progressive MS and found that 13 patients (57%) lacked this sympathetic-mediated response. The density of beta-adrenergic receptors on lymphocyte subsets was increased in progressive MS, most notably on the CD8 suppressor/cytotoxic subset. B lymphocytes had the greatest number of receptors with 12.1 +/- 1.8 fmol/10(6) cells in control subjects and 18.7 +/- 2.6 fmol/10(6) cells in patients with MS. CD8 lymphocytes possessed an intermediate number of receptors with 3.4 +/- 0.4 fmol/10(6) cells in control subjects and 9.1 +/- 1.6 fmol/10(6) cells in patients with MS. CD4 lymphocytes demonstrated the fewest receptors with 1.2 +/- 0.1 fmol/10(6) cells in control subjects and 1.8 +/- 0.4 fmol/10(6) cells in patients with MS. No differences in the affinity or function (cyclic adenosine monophosphate levels in response to 10(-5) M (-)isoproterenol) of the adrenergic receptor were found when patients with progressive MS and control subjects were compared. Autonomic abnormalities in progressive MS and the increased beta-adrenergic receptor density found on CD8 lymphocytes may be related.

Multiple sclerosis: possible immunological mechanisms

Multiple sclerosis is the principal demyelinating disease of the central nervous system. Although the prevalence of the disease is moderately low, averaging about 40 cases per 100,000 people in high risk areas, it is a particularly devastating disease. It primarily affects young adults, is chronic, and has an unpredictable course. Most discouraging, the cause of the disease is not known and an effective treatment has not been identified. Recently, however, research has yielded some important findings concerning the etiology of MS. Much evidence now points to an immunological process as one of the major elements in the disease. It is also likely that an environmental influence, possibly an infectious process, may contribute to the disease. Finally, it is now certain that genetic makeup influences susceptibility to the disease. At present, the strongest evidence is for a polygenic effect, not the effect of a single gene or gene locus. This review will examine some of the possible immunologically mediated disease processes that could be involved in MS, especially those that could account for a role for infectious and genetic factors in the disease.

Peripheral blood lymphocyte phenotype and function in multiple sclerosis

T suppressor cell function and phenotype are abnormal in patients with multiple sclerosis, especially during the chronic progressive phase but the sub-populations defined by mitogen stimulation and serological methods may not be identical. In this study, involving 45 patients with multiple sclerosis and 33 controls, there was no correlation between T suppressor function and CD8 cell phenotype in patients with multiple sclerosis or in controls. These phenotypic and functional studies cannot therefore be used interchangeably in the assessment of patients with multiple sclerosis since they provide different information about lymphocyte subpopulations.

The imbalance in CSF T cell subsets in active multiple sclerosis

We determined the percentage of each lymphocyte subpopulation in the cerebrospinal fluid (CSF) and the peripheral blood of 7 patients with active multiple sclerosis (MS), 7 with inactive MS, 5 with other inflammatory diseases in the central nervous system, and 12 with non-inflammatory neurological diseases, using fluorescein-labelled monoclonal antibodies (anti-Leu7, anti-HLA-DR, and those that recognize such surface antigens as CD3, CD4, CD8, and CD19), and by laser flow cytometry to clarify the clinical usefulness of their measurement in the assessment of disease activity in MS. In CSF, a significant increase in the percentage of CD4+ cells and a significant decrease in the percentage of CD8+ cells were observed in the active MS group compared with the other 3 groups, while none of the percentages of the 6 subsets studied in the peripheral blood were significantly different among these groups. Our preliminary study indicated that evaluation of the percentages of CD4+ and CD8+ cells in CSF by flow cytometry could be a useful indicator of disease activity in MS.

CD4+ T cell activation in multiple sclerosis

Interleukin-2 (IL-2) production by CD4-enriched T cells from multiple sclerosis (MS) patients and normal individuals stimulated with concanavalin A (conA) and/or autologous and allogeneic B lymphoid cell lines (B-LCL) was evaluated 24, 48 and 96 h after stimulation. ConA-stimulated CD4+ cells from MS patients did not produce significantly more IL-2 than normal CD4+ cells. In contrast, autologous B-LCL-induced IL-2 production by MS CD4+ cells significantly (P = 0.026) exceeded that produced by normal CD4+ cells identically stimulated after 24 h in culture. Differences in IL-2 production by CD4+ cells from MS patients reached highest significance using allogeneic B-LCL, whose stimulatory capacity was similar, whether established from normal individuals or MS patients. This increased IL-2 production in response to B-LCL may represent a supranormal response of CD4+ cells from MS patients to class II major histocompatibility (MHC)-associated stimuli. It suggests that the deficiency of suppressor T cell functions postulated to play a role in MS does not arise from a lack of IL-2 induction and might indicate that bursts of IL-2 production could play a role in MS.