Mechanism of gammadelta T cell-induced human oligodendrocyte cytotoxicity: relevance to multiple sclerosis

Neuro-immune crosstalk in depressive symptoms of multiple sclerosis

Depressive disorders can occur in up to 50% of people with multiple sclerosis in their lifetime. If left untreated, comorbid major depressive disorders may not spontaneously remit and is associated with an increased morbidity and mortality. Conversely, epidemiological evidence supports increased psychiatric visit as a significant prodromal event prior to diagnosis of MS. Are there common molecular pathways that contribute to the co-development of MS and psychiatric illnesses? We discuss immune cells that are dysregulated in MS and how such dysregulation can induce or protect against depressive symptoms. This is not meant to be a comprehensive review of all molecular pathways but rather a framework to guide future investigations of immune responses in depressed versus euthymic people with MS. Currently, there is weak evidence supporting the use of antidepressant medication in comorbid MS patients. It is our hope that by better understanding the neuroimmune crosstalk in the context of depression in MS, we can enhance the potential for future therapeutic options.

The immunology of multiple sclerosis

Our incomplete understanding of the causes and pathways involved in the onset and progression of multiple sclerosis (MS) limits our ability to effectively treat this complex neurological disease. Recent studies explore the role of immune cells at different stages of MS and how they interact with cells of the central nervous system (CNS). The findings presented here begin to question the exclusivity of an antigen-specific cause and highlight how seemingly distinct immune cell types can share common functions that drive disease. Innovative techniques further expose new disease-associated immune cell populations and reinforce how environmental context is critical to their phenotype and subsequent role in disease. Importantly, the differentiation of immune cells into a pathogenic state is potentially reversible through therapeutic manipulation. As such, understanding the mechanisms that provide plasticity to causal cell types is likely key to uncoupling these disease processes and may identify novel therapeutic targets that replace the need for cell ablation.

γδ T Cells in Brain Homeostasis and Diseases

γδ T cells are a distinct subset of T cells expressing γδ T cell receptor (TCR) rather than αβTCR. Since their discovery, the critical roles of γδ T cells in multiple physiological systems and diseases have been investigated. γδ T cells are preferentially located at mucosal surfaces, such as the gut, although a small subset of γδ T cells can circulate the blood. Additionally, a subset of γδ T cells reside in the meninges in the central nervous system. Recent findings suggest γδ T cells in the meninges have critical roles in brain function and homeostasis. In addition, several lines of evidence have shown γδ T cells can infiltrate the brain parenchyma and regulate inflammatory responses in multiple diseases, including neurodegenerative diseases. Although the importance of γδ T cells in the brain is well established, their roles are still incompletely understood due to the complexity of their biology. Because γδ T cells rapidly respond to changes in brain status and regulate disease progression, understanding the role of γδ T cells in the brain will provide critical information that is essential for interpreting neuroimmune modulation. In this review, we summarize the complex role of γδ T cells in the brain and discuss future directions for research.

Contemplating Dichotomous Nature of Gamma Delta T Cells for Immunotherapy

γδ T cells are unconventional T cells, distinguished from αβ T cells in a number of functional properties. Being small in number compared to αβ T cells, γδ T cells have surprised us with their pleiotropic roles in various diseases. γδ T cells are ambiguous in nature as they can produce a number of cytokines depending on the (micro) environmental cues and engage different immune response mechanisms, mainly due to their epigenetic plasticity. Depending on the disease condition, γδ T cells contribute to beneficial or detrimental response. In this review, we thus discuss the dichotomous nature of γδ T cells in cancer, neuroimmunology and infectious diseases. We shed light on the importance of equal consideration for systems immunology and personalized approaches, as exemplified by changes in metabolic requirements. While providing the status of immunotherapy, we will assess the metabolic (and other) considerations for better outcome of γδ T cell-based treatments.

Neurological Benefits, Clinical Challenges, and Neuropathologic Promise of Medical Marijuana: A Systematic Review of Cannabinoid Effects in Multiple Sclerosis and Experimental Models of Demyelination

Despite current therapeutic strategies for immunomodulation and relief of symptoms in multiple sclerosis (MS), remyelination falls short due to dynamic neuropathologic deterioration and relapses, leading to accrual of disability and associated patient dissatisfaction. The potential of cannabinoids includes add-on immunosuppressive, analgesic, neuroprotective, and remyelinative effects. This study evaluates the efficacy of medical marijuana in MS and its experimental animal models. A systematic review was conducted by a literature search through PubMed, ProQuest, and EBSCO electronic databases for studies reported since 2007 on the use of cannabidiol (CBD) and delta-9-tetrahydrocannabinol (THC) in MS and in experimental autoimmune encephalomyelitis (EAE), Theiler’s murine encephalomyelitis virus-induced demyelinating disease (TMEV-IDD), and toxin-induced demyelination models. Study selection and data extraction were performed by 3 reviewers, and 28 studies were selected for inclusion. The certainty of evidence was appraised using the Cochrane GRADE approach. In clinical studies, there was low- and moderate-quality evidence that treatment with ~1:1 CBD/THC mixtures as a nabiximols (Sativex®) oromucosal spray reduced numerical rating scale (NRS) scores for spasticity, pain, and sleep disturbance, diminished bladder overactivity, and decreased proinflammatory cytokine and transcription factor expression levels. Preclinical studies demonstrated decreases in disease severity, hindlimb stiffness, motor function, neuroinflammation, and demyelination. Other experimental systems showed the capacity of cannabinoids to promote remyelination in vitro and by electron microscopy. Modest short-term benefits were realized in MS responders to adjunctive therapy with CBD/THC mixtures. Future studies are recommended to investigate the cellular and molecular mechanisms of cannabinoid effects on MS lesions and to evaluate whether medical marijuana can accelerate remyelination and retard the accrual of disability over the long term.

NK Cells and Innate-Like T Cells After Autologous Hematopoietic Stem Cell Transplantation in Multiple Sclerosis

Multiple sclerosis (MS) is an autoimmune disease of the central nervous system, in which autoreactive T and B cells play important roles. Other lymphocytes such as NK cells and innate-like T cells appear to be involved as well. To name a few examples, CD56^bright NK cells were described as an immunoregulatory NK cell subset in MS while innate-like T cells in MS were described in brain lesions and with proinflammatory signatures. Autologous hematopoietic stem cell transplantation (aHSCT) is a procedure used to treat MS. This procedure includes hematopoietic stem/progenitor cell (HSPC) mobilization, then high-dose chemotherapy combined with anti-thymocyte globulin (ATG) and subsequent infusion of the patients own HSPCs to reconstitute a functional immune system. aHSCT inhibits MS disease activity very effectively and for long time, presumably due to elimination of autoreactive T cells. Here, we performed multidimensional flow cytometry experiments in peripheral blood lymphocytes of 27 MS patients before and after aHSCT to address its potential influence on NK and innate-like T cells. After aHSCT, the relative frequency and absolute numbers of CD56^bright NK cells rise above pre-aHSCT levels while all studied innate-like T cell populations decrease. Hence, our data support an enhanced immune regulation by CD56^bright NK cells and the efficient reduction of proinflammatory innate-like T cells by aHSCT in MS. These observations contribute to our current understanding of the immunological effects of aHSCT in MS.

T cell transgressions: Tales of T cell form and function in diverse disease states

Insights into T cell form, function, and dysfunction are rapidly evolving. T cells have remarkably varied effector functions including protecting the host from infection, activating cells of the innate immune system, releasing cytokines and chemokines, and heavily contributing to immunological memory. Under healthy conditions, T cells orchestrate a finely tuned attack on invading pathogens while minimizing damage to the host. The dark side of T cells is that they also exhibit autoreactivity and inflict harm to host cells, creating autoimmunity. The mechanisms of T cell autoreactivity are complex and dynamic. Emerging research is elucidating the mechanisms leading T cells to become autoreactive and how such responses cause or contribute to diverse disease states, both peripherally and within the central nervous system. This review provides foundational information on T cell development, differentiation, and functions. Key T cell subtypes, cytokines that create their effector roles, and sex differences are highlighted. Pathological T cell contributions to diverse peripheral and central disease states, arising from errors in reactivity, are highlighted, with a focus on multiple sclerosis, rheumatoid arthritis, osteoarthritis, neuropathic pain, and type 1 diabetes.

Phenotypic and functional changes in gamma delta T lymphocytes from HTLV-1 carriers

Human T-cell lymphotropic virus type-1 (HTLV-1) is the etiologic agent of HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP), which is a chronic inflammatory disease that leads to gradual loss of motor movement as a result of the death of spinal cord cells through immune mediated mechanisms. The risk to develop HAM/TSP disease positively correlates with the magnitude of HTLV-1 proviral load. Gamma-delta T lymphocytes have been recognized as important players in a variety of infectious diseases. Therefore, we have investigated interactions between HTLV-1 infection and γδ T lymphocytes during HAM/TSP. Similar frequencies of total γδ T lymphocytes and their Vγ9δ2⁺ and Vγ9δ2^neg subpopulations were observed in HAM/TSP patients. However, T lymphocytes obtained from HTLV-1 carriers displayed significantly higher rates of spontaneous proliferation and NKp30 expression when compared to cells from uninfected donors. In addition, an important decrease in the frequency of granzyme B⁺ γδ T lymphocytes (approximately 50%) was observed in HAM/TSP patients. Higher proportion of IFN-γ⁺ γδ T lymphocytes was found in HTLV-1-infected patients, which positively correlated with the HTLV-1 proviral load in peripheral blood mononuclear cells. Collectively, our data indicates that HTLV-1 infection leads to phenotypic and functional changes in the population of γδ T lymphocyte population, suggesting that HTLV-1 infection modulates functions associated to these cells, which might be involved in controlling the infection or in the development of HTLV-1-associated diseases.

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.

γδ T lymphocytes in the pathogenesis of multiple sclerosis and experimental autoimmune encephalomyelitis

The aim of the current review is to summarize the results of studies on the role of γδ T cells in the pathogenesis of multiple sclerosis and its animal model - the experimental autoimmune encephalomyelitis. Despite the fact that numerous studies have been performed, the role of γδ T is still not fully understood. It seems that there are two distinct subpopulations - one exacerbating the disease (IL-17-producing) and the other playing a protective role (IFN-γ-secreting). Nevertheless, future studies are required for an understanding of γδ T cells role in multiple sclerosis.

γδ T Lymphocytes: An Effector Cell in Autoimmunity and Infection

γδ T cells are non-conventional lymphocytes which show several properties of innate immune cells. They present a limited TCR repertoire and circulate as cells with a pre-activated phenotype thus being able to generate rapid immune responses. γδ T cells do not recognize classical peptide antigens, their TCRs are non-MHC restricted and they can respond to pathogen-associated molecular patterns and to cytokines in absence of TCR ligands. They also recognize self-molecules induced by stress, which indicate infection and cellular transformation. All these features let γδ T cells act as a first line of defense in sterile and non-sterile inflammation. γδ T cells represent 1–10% of circulating lymphocytes in the adult human peripheral blood, they are widely localized in non-lymphoid tissues and constitute the majority of immune cells in some epithelial surfaces, where they participate in the maintenance of the epithelial barriers. γδ T cells produce a wide range of cytokines that orchestrate the course of immune responses and also exert high cytotoxic activity against infected and transformed cells. In contrast to their beneficial role during infection, γδ T cells are also implicated in the development and progression of autoimmune diseases. Interestingly, several functions of γδ T cells are susceptible to modulation by interaction with other cells. In this review, we give an overview of the γδ T cell participation in infection and autoimmunity. We also revise the underlying mechanisms that modulate γδ T cell function that might provide tools to control pathological immune responses.

Association of Decreased Percentage of Vδ2+Vγ9+ γδ T Cells With Disease Severity in Multiple Sclerosis

We recently reported that deletion-type copy number variations of the T cell receptor (TCR) γ, α, and δ genes greatly enhanced susceptibility to multiple sclerosis (MS). However, the effect of abnormal TCR γδ gene rearrangement on MS pathogenesis remains unknown. In the present study, we aimed to clarify γδ TCR repertoire alterations and their relationship to clinical and immunological parameters in MS patients by comprehensive flow cytometric immunophenotyping. Peripheral blood mononuclear cells obtained from 30 untreated MS patients in remission and 23 age- and sex-matched healthy controls (HCs) were stained for surface markers and intracellular cytokines after stimulation with phorbol 12-myristate 13-acetate and ionomycin, and analyzed by flow cytometry. MS patients showed significantly decreased percentages of Vδ2⁺ and Vδ2⁺Vγ9⁺ cells in γδ T cells (p^corr = 0.0297 and p^corr = 0.0288, respectively) and elevated Vδ1/Vδ2 ratios compared with HCs (p = 0.0033). The percentages of interferon (IFN)-γ⁺Vδ2⁺ and interleukin (IL)-17A⁺IFN-γ⁺Vδ2⁺ cells in γδ T cells, as well as IFN-γ⁺ cells in Vδ2⁺ γδ T cells, were significantly lower in MS patients than in HCs (p^corr < 0.0009, p^corr = 0.0135, and p^corr = 0.0054, respectively). The percentages of Vδ2⁺ and Vδ2⁺Vγ9⁺ cells in γδ T cells were negatively correlated with both the Expanded Disability Status Scale score (r = -0.5006, p = 0.0048; and r = -0.5040, p = 0.0045, respectively) and Multiple Sclerosis Severity Score (r = -0.4682, p = 0.0091; and r = -0.4706, p = 0.0087, respectively), but not with age at disease onset, disease duration, or annualized relapse rate. In HCs, the percentages of Vδ2⁺ and Vδ2⁺Vγ9⁺ cells of total CD3⁺ T cells had strong positive correlations with the percentage of CD25⁺CD127^low/- cells in CD4⁺ T cells (r = 0.7826, p < 0.0001; and r = 0.7848, p < 0.0001, respectively), whereas such correlations were totally absent in MS patients. These findings suggest that decreased Vδ2⁺Vγ9⁺ γδ T cells are associated with disability in MS. Therefore, the Vδ1/Vδ2 ratio might be a candidate biomarker for predicting disease severity in MS.

Th17 cells, γδ T cells and their interplay in EAE and multiple sclerosis

Experimental autoimmune encephalomyelitis (EAE) is an animal model of multiple sclerosis (MS) that shares many features with the human disease. This review will focus on the role of IL-17-secreting CD4 and γδ T cells in EAE and MS, the plasticity of Th17 cells in vivo and the application of these findings to the understating of the pathogenesis and the development of new treatments for MS. There is convincing evidence that IL-17-secreting CD4 T cells (Th17 cells) and IL-17-secreting γδ T cells play a critical pathogenic role in central nervous system (CNS) inflammation in EAE and MS. Indeed a significant number of the major discoveries on the pathogenic role of IL-17-secreting T cells in autoimmunity were made in the EAE model. These included the first demonstration that IL-23-activated IL-17-secreting T cells are the key T cells in driving autoimmune disease pathology. Although the early studies on IL-17 focused on Th17 cells, it was later demonstrated that γδ T cells were an important early source of IL-17 and IL-21 that helped amplify IL-17 production by Th17 cells in autoimmune diseases. Furthermore, it emerged that Th1 cells can also have encephalitogenic activity and that there was considerable plasticity in these T cell responses, with Th17 cells reverting to a Th1 phenotype in vivo. This questioned the pathogenic role of IL-17 and suggested that other cytokines, such as IFN-γ, GM-CSF and TNF, may be important. Nevertheless, biological drugs that target the IL-23-IL-17 pathway are highly effective in treating human psoriasis and are showing promise in the treatment of relapsing remitting MS and other T-cell mediated autoimmune diseases.

Traumatic brain injury causes selective, CD74-dependent peripheral lymphocyte activation that exacerbates neurodegeneration

Introduction

Traumatic brain injury (TBI), a significant cause of death and disability, causes, as in any injury, an acute, innate immune response. A key component in the transition between innate and adaptive immunity is the processing and presentation of antigen by professional antigen presenting cells (APCs). Whether an adaptive immune response to brain injury is beneficial or detrimental is not known. Current efforts to understand the contribution of the immune system after TBI have focused on neuroinflammation and brain-infiltrating immune cells. Here, we characterize and target TBI-induced expansion of peripheral immune cells that may act as potential APCs. Because MHC Class II-associated invariant peptide (CLIP) is important for antigen processing and presentation, we engineered a competitive antagonist (CAP) for CLIP, and tested the hypothesis that peptide competition could reverse or prevent neurodegeneration after TBI.

Results

We show that after fluid percussion injury (FPI), peripheral splenic lymphocytes, including CD4+ and CD8+ T cells, regulatory T cells (Tregs), and γδ T cells, are increased in number within 24 hours after FPI. These increases were reversed by CAP treatment and this antagonism of CLIP also reduced neuroinflammation and neurodegeneration after TBI. Using a mouse deficient for the precursor of CLIP, CD74, we observed decreased peripheral lymphocyte activation, decreased neurodegeneration, and a significantly smaller lesion size following TBI.

Conclusion

Taken together, the data support the hypothesis that neurodegeneration following TBI is dependent upon antigen processing and presentation that requires CD74.

Electronic supplementary material

The online version of this article (doi:10.1186/s40478-014-0143-5) contains supplementary material, which is available to authorized users.

Human Vγ9Vδ2-T cells efficiently kill influenza virus-infected lung alveolar epithelial cells

γδ-T cells play an indispensable role in host defense against different viruses, including influenza A virus. However, whether these cells have cytotoxic activity against influenza virus-infected lung alveolar epithelial cells and subsequently contribute to virus clearance remains unknown. Using influenza virus-infected A549 cells, human lung alveolar epithelial cells, we investigated the cytotoxic activity of aminobisphosphonate pamidronate (PAM)-expanded human Vγ9Vδ2-T cells and their underlying mechanisms. We found that PAM could selectively activate and expand human Vγ9Vδ2-T cells. PAM-expanded human Vγ9Vδ2-T cells efficiently killed influenza virus-infected lung alveolar epithelial cells and inhibited virus replication. The cytotoxic activity of PAM-expanded Vγ9Vδ2-T cells was dependent on cell-to-cell contact and required NKG2D activation. Perforin-granzyme B, tumor-necrosis factor-related apoptosis-inducing ligand (TRAIL) and Fas-Fas ligand (FasL) pathways were involved in their cytotoxicity. Our study suggests that targeting γδ-T cells by PAM can potentially offer an alternative option for the treatment of influenza virus.

The aminobisphosphonate pamidronate controls influenza pathogenesis by expanding a gammadelta T cell population in humanized mice

As shown in humanized mice, a population of Vγ9Vδ2 T cells can reduce the severity and mortality of disease caused by infection with human and avian influenza viruses.

There are few antiviral drugs for treating influenza, and the emergence of antiviral resistance has further limited the available therapeutic options. Furthermore, antivirals are not invariably effective in severe influenza, such as that caused by H5N1 viruses. Thus, there is an urgent need to develop alternative therapeutic strategies. Here, we show that human Vγ9Vδ2 T cells expanded by the aminobisphosphonate pamidronate (PAM) kill influenza virus–infected cells and inhibit viral replication in vitro. In Rag2^−/−γc^−/− immunodeficient mice reconstituted with human peripheral mononuclear cells (huPBMCs), PAM reduces disease severity and mortality caused by human seasonal H1N1 and avian H5N1 influenza virus, and controls the lung inflammation and viral replication. PAM has no such effects in influenza virus–infected Rag2^−/−γc^−/− mice reconstituted with Vγ9Vδ2 T cell–depleted huPBMCs. Our study provides proof-of-concept of a novel therapeutic strategy for treating influenza by targeting the host rather than the virus, thereby reducing the opportunity for the emergence of drug-resistant viruses. As PAM has been commonly used to treat osteoporosis and Paget’s disease, this new application of an old drug potentially offers a safe and readily available option for treating influenza.

γδ T cells and multiple sclerosis: Friends, foes, or both?

Multiple sclerosis (MS) is a debilitating CNS disease characterized by demyelination and neuro-axonal loss. Though the exact etiology is still unknown, accumulated evidence points to the immune system being involved in the MS disease-process. Both ill-fated adaptive and innate immune responses can potentially contribute to the etiopathogenesis. We have been interested in deciphering how innate immunity might be involved; in particular, the role of γδ T cells. In this review, we discuss the current understanding about γδ T cells and describe the evidence implicating them in myelin injury, neurotoxicity, and immunoregulation in the development of MS.

Importance of oligodendrocyte protection, BBB breakdown and inflammation for remyelination

Multiple sclerosis (MS) is a chronic inflammatory demyelinating disease of the CNS. A better understanding of why remyelination fails in MS is necessary to improve remyelination strategies. Remyelination is mediated by oligodendrocyte precursor cells (OPCs), which are widely distributed throughout the adult CNS. However, it is still unclear whether OPCs detectable in MS lesions survive the inflammatory response but are unable to myelinate or whether OPC and oligodendrocyte death is primarily responsible for remyelination failure and detectable OPCs enter demyelinated areas from adjacent tissue as the lesion evolves. Remyelination strategies should, therefore, focus on stimulation of differentiation or prevention of apoptosis, as well as establishment of a supportive environment for OPC-mediated remyelination, which may be especially important in chronically demyelinated lesions.

Role of the innate immune system in the pathogenesis of multiple sclerosis

Multiple sclerosis (MS) is a chronic inflammatory autoimmune disease with heterogeneous clinical presentations and course. MS is considered to be a T cell mediated disease but in recent years contribution of innate immune cells in mediating MS pathogenesis is being appreciated. In this review, we have discussed the role of various innate immune cells in mediating MS. In particular, we have provided an overview of potential anti-inflammatory or pro-inflammatory function of DCs, microglial Cells, NK cells, NK-T cells and gamma delta T cells along with their interaction among themselves and with myelin. Given the understanding of the role of the innate immune cells in MS, it is possible that immunotherapeutic intervention targeting these cells may provide a better and effective treatment.

gammadelta T cells: the overlooked T-cell subset in demyelinating disease

gammadelta T cells represent a small subpopulation of T cells expressing a restricted repertoire of T-cell receptors and, unlike alphabeta T cells, function more as cells of the innate immune system. These cells are found in skin and mucosal sites as well as secondary lymphoid tissues and frequently act as first line of defense sentinels. gammadelta T cells have been implicated in the pathogenesis of demyelinating disease, although little was known regarding their trafficking and effector functions. In this Mini-Review, we highlight recent studies demonstrating that gammadelta T cells migrate rapidly to the CNS during experimental autoimmune encephalomyelitis (EAE), the animal model for multiple sclerosis. gammadelta T-cell trafficking to the CNS is independent of beta(2)-integrins and occurs well before onset of clinical signs of disease, peaking early during the acute phase of disease. gammadelta T-cell-mediated production of inflammatory cytokines, including interferon-gamma and tumor necrosis factor-alpha, appears critical for EAE development, suggesting that these cells may set the stage for activation of other subsets of infiltrating effector cells. These data suggest that gammadelta T cells or subsets of gammadelta T cells may represent a new therapeutic target in demeylinating disease.

Phosphoantigen-expanded human gammadelta T cells display potent cytotoxicity against monocyte-derived macrophages infected with human and avian influenza viruses

BackgroundInfluenza virus is a cause of substantial annual morbidity and mortality worldwide. The potential emergence of a new pandemic strain (eg, avian influenza virus) is a major concern. Currently available vaccines and anti-influenza drugs have limited effectiveness for influenza virus infections, especially for new pandemic strains. Therefore, there is an acute need to develop alternative strategies for influenza therapy. γδ T cells have potent antiviral activities against different viruses, but no data are available concerning their antiviral activity against influenza viruses

MethodsIn this study, we used virus-infected primary human monocyte-derived macrophages (MDMs) to examine the antiviral activity of phosphoantigen isopentenyl pyrophosphate (IPP)–expanded human Vγ9Vδ2 T cells against influenza viruses

ResultsVγ9Vδ2 T cells were selectively activated and expanded by IPP from peripheral blood mononuclear cells. IPP-expanded Vγ9Vδ2 T cells efficiently killed MDMs infected with human (H1N1) or avian (H9N2 or H5N1) influenza virus and significantly inhibited viral replication. The cytotoxicity of Vγ9Vδ2 T cells against influenza virus–infected MDMs was dependent on NKG2D activation and was mediated by Fas–Fas ligand and perforin–granzyme B pathways

ConclusionOur findings suggest a potentially novel therapeutic approach to seasonal, zoonotic avian, and pandemic influenza—the use of phosphoantigens to activate γδ T cells against influenza virus infections

Neuroprotective effects of the complement terminal pathway during demyelination: implications for oligodendrocyte survival

Multiple sclerosis (MS) is a chronic inflammatory demyelinating disease of the central nervous system that is mediated by activated lymphocytes, macrophages/microglia, and complement. In MS, the myelin-forming oligodendrocytes (OLGs) are the targets of the immune attack. Experimental evidence indicates that C5b-9 plays a role in demyelination during the acute phase of experimental allergic encephalomyelitis (EAE). Terminal complement C5b-9 complexes are capable of protecting OLGs from apoptosis. During chronic EAE complement C5 promotes axonal preservation, remyelination and provides protection from gliosis. These findings indicate that the activation of complement and C5b-9 assembly can also have protective roles during demyelination.

Intracellular versus extracellular granzyme B in immunity and disease: challenging the dogma

The cytotoxic granzyme B (GrB)/perforin pathway has been traditionally viewed as a primary mechanism that is used by cytotoxic lymphocytes to eliminate allogeneic, virally infected and/or transformed cells. Although originally proposed to have intracellular and extracellular functions, upon the discovery that perforin, in combination with GrB, could induce apoptosis, other potential functions for this protease were, for the most part, disregarded. As there are 5 granzymes in humans and 11 granzymes in mice, many studies used perforin knockout mice as an initial screen to evaluate the role of granzymes in disease. However, in recent years, emerging clinical and biochemical evidence has shown that the latter approach may have overlooked a critical perforin-independent, pathogenic role for these proteases in disease. This review focuses on GrB, the most characterized of the granzyme family, in disease. Long known to be a pro-apoptotic protease expressed by cytotoxic lymphocytes and natural killer cells, it is now accepted that GrB can be expressed in other cell types of immune and nonimmune origin. To the latter, an emerging immune-independent role for GrB has been forwarded due to recent discoveries that GrB may be expressed in nonimmune cells such as smooth muscle cells, keratinocytes, and chondrocytes in certain disease states. Given that GrB retains its activity in the blood, can cleave extracellular matrix, and its levels are often elevated in chronic inflammatory diseases, this protease may be an important contributor to certain pathologies. The implications of sustained elevations of intracellular and extracellular GrB in chronic vascular, dermatological, and neurological diseases, among others, are developing. This review examines, for the first time, the multiple roles of GrB in disease pathogenesis.

Innate immune-mediated neuronal injury consequent to loss of astrocytes

Neuronal injury and loss are recognized features of neuroinflammatory disorders, including acute and chronic encephalitides and multiple sclerosis; destruction of astrocytes has been demonstrated in cases of Rasmussen encephalitis. Here, we show that innate immune cells (i.e. natural killer [NK] and gammadelta T cells) cause loss of neurons from primary human neuron-enriched cultures by destroying the supporting astrocytes. Interleukin 2-activated NK cells caused loss of astrocytes within 1 hour, whereas neurons were lost at 4 hours. Time-lapse imaging indicated that delayed neuron loss was due to early destruction of supporting astrocytes. Selective blocking of astrocyte death with anti-NKG2D antibodies reduced neuron loss, as did blocking of CD54 on astrocytes. gammadelta T cells also induced astrocyte cytotoxicity, leading to subsequent neuronal displacement. In astrocytes, NK cells caused caspase-dependent fragmentation of the intermediate filament proteins glial fibrillary acidic protein and vimentin, whereas anti-CD3-activated T cells produced fragmentation to a lesser extent and without measurable cytotoxicity. Glial fibrillary acidic protein fragmentation was also demonstrated in lysates from chronic multiple sclerosis plaques but not from normal control white matter. These data suggest that non-major histocompatibility complex-restricted immune effector cells may contribute to neuron loss in neuroinflammatory disorders indirectly through injury of glia.

CD16+ gammadelta T cells mediate antibody dependent cellular cytotoxicity: potential mechanism in the pathogenesis of multiple sclerosis

Our overall objective is to understand the role of gammadelta T cells in the pathogenesis of the central nervous system (CNS) autoimmune disease multiple sclerosis (MS). We have demonstrated that gammadelta T cells are directly cytotoxic to CNS cells in vitro. Although the exact mechanism of damage in MS is unknown, recent evidence suggests a role for B cells and antibodies to myelin. We were therefore interested in examining whether gammadelta T cells can injure CNS cells via an indirect mechanism involving antibody dependent cellular cytotoxicity. To study this we developed an in vitro flow cytometric cellular cytotoxicity assay (called "FC(3)A") to quantitate the amount of cytotoxicity. We utilized known target cells (Burkitt's B lymphoma) that express CD20, together with a monoclonal antibody (mAb) to CD20, rituximab, that is being studied as a potential treatment for MS. Target cells are first coated with rituximab followed by co-culture with gammadelta T cells derived from patients with MS. Specific lysis of target cells was determined by quantitation of 7-AAD (which increases only upon nuclear disruption indicating cell death). We determined that this lysis was due to gammadelta T cells that express CD16 (Fc gamma receptor) and were therefore capable of binding the rituximab and mediating cytolysis via ADCC. This specific cell lysis correlated with rituximab concentration, E:T ratio, and the surface expression of CD16 on gammadelta T cells. These findings provide a new perspective with regards to the role of gammadelta T cells in the immunopathogenesis of MS and an insight into one of the potential therapeutic effects of rituximab in the treatment of MS. In addition, this new FC(3)A method we developed could readily be adapted to study other types of immune cells suspected of ADCC-type killing.

The multiple sclerosis degradome: enzymatic cascades in development and progression of central nervous system inflammatory disease

An array of studies implicate different classes of protease and their endogenous inhibitors in multiple sclerosis (MS) pathogenesis based on expression patterns in MS lesions, sera, and/or cerebrospinal fluid (CSF). Growing evidence exists regarding their mechanistic roles in inflammatory and neurodegenerative aspects of this disease. Proteolytic events participate in demyelination, axon injury, apoptosis, and development of the inflammatory response including immune cell activation and extravasation, cytokine and chemokine activation/inactivation, complement activation, and epitope spreading. The potential significance of proteolytic activity to MS therefore relates not only to their potential use as important biomarkers of disease activity, but additionally as prospective therapeutic targets. Experimental data indicate that understanding the net physiological consequence of altered protease levels in MS development and progression necessitates understanding protease activity in the context of substrates, endogenous inhibitors, and proteolytic cascade interactions, which together make up the MS degradome. This review will focus on evidence regarding the potential physiologic role of those protease families already identified as markers of disease activity in MS; that is, the metallo-, serine, and cysteine proteases.

Correlation of specialized CD16(+) gammadelta T cells with disease course and severity in multiple sclerosis

gammadelta T cells may be important innate immune system contributors to the immunopathogenesis of multiple sclerosis (MS), though the mechanisms are not yet fully understood. CD16 is a low affinity Fcgamma receptor, an activation receptor for gammadelta T cells, and a mediator of cytotoxicity. In this study, we found that the percentage of CD16(+) gammadelta T cells is elevated in MS patients compared with healthy controls. The increase is especially pronounced in patients with a progressive course of the disease, and the extent of this elevation shows a positive correlation with the time of disease progression and severity. In vitro cultured gammadelta T cells can be shown to upregulate the expression of CD16 in response to inflammatory cytokines such as IL-2 and -15, that have been shown to be elevated in progressive disease. These results suggest that CD16 expressing gammadelta T cells are somehow involved in the process of disease progression. Understanding more about these cells and their particular function in progressive vs. non-progressive disease could provide important clues to the mechanism of immune-mediated MS disease progression.

Effectors of demyelination and remyelination in the CNS: implications for multiple sclerosis

Most of the research on multiple sclerosis (MS) has focused on the early events that trigger demyelination and subsequent remyelination. Less attention has been given to the factors that directly mediate the demyelination that is the hallmark of the disease. Effector cells or molecules are those factors directly responsible for mediating the damage in the disease. Similarly, there are effector molecules that are critical for remyelination in the central nervous system (CNS). By understanding those effector molecules in demyelination and remyelination that directly influence the pathologic process, we should be able to generate specific therapies with the greatest potential for benefiting MS patients. This review focuses on effector cells and molecules that are critical for demyelination and remyelination in MS but also in experimental models of the disease including experimental autoimmune encephalomyelitis (EAE), virus-induced models of demyelination (Theiler's virus, murine hepatitis virus), and toxic models of demyelination (lysolecithin, ethidium bromide, and cuprizone). These are models in which the effector molecules for demyelination and remyelination have been most precisely evaluated.

NKG2D-mediated cytotoxicity toward oligodendrocytes suggests a mechanism for tissue injury in multiple sclerosis

NKG2D is an activating or coactivating receptor expressed on human natural killer (NK) cells, CD8+ T cells, and gamma/delta T cells. NKG2D ligands have been detected on many tumor cell types and can be induced on nontransformed cells by environmental signals including DNA damage and inflammation. We investigated the contribution of NKG2D-NKG2D ligand interaction on CNS-directed immune responses. We observed that primary cultures of human adult oligodendrocytes and fetal astrocytes expressed ligands for NKG2D in vitro whereas neurons, microglia, and adult astrocytes did not. Disruption of the NKG2D-NKG2D ligand interaction using blocking antibodies significantly inhibited killing of primary human oligodendrocytes mediated by activated human NK cells, gamma/delta T cells, and allo-reactive CD8+ T cells. NKG2D ligands [major histocompatibility complex class I chain-related molecules A and B (MICA/B)] were detected in groups of cells and colocalized with an oligodendrocyte marker (adenomatous polyposis coli) in white matter sections obtained from multiple sclerosis lesions but not in normal control samples. CD8+ T cells could be detected in close proximity to MICA/B+ cells within multiple sclerosis lesions, supporting an in vivo interaction between these immune effectors and stressed MICA/B-expressing oligodendrocytes. These results imply that NKG2D-NKG2D ligand interaction can potentially contribute to cytotoxic responses mediated by activated immune effector cells in the inflamed CNS, as observed in multiple sclerosis.

Leukemia inhibitory factor is produced by myelin-reactive T cells from multiple sclerosis patients and protects against tumor necrosis factor-α-induced oligodendrocyte apoptosis

In multiple sclerosis (MS), damage to oligodendrocytes is believed to be caused by an aberrant immune response initiated by autoreactive T cells. Increasing evidence indicates that these T cells are not exclusively detrimental but might also exert protective effects. We report for the first time that myelin-reactive T-cell clones from eight MS patients (6/19) and five healthy controls (4/11) produce leukemia inhibitory factor (LIF), a member of the neuropoietic family of neurotrophins. In addition, T-cell clones specific for tetanus toxoid, CD4(+) and CD8(+) T cells, and monocytes, but not B cells, secreted LIF. LIF-producing T lymphocytes and macrophages were also identified immunohistochemically in both active and chronic-active MS lesions. We further demonstrated dose-dependent protective effects of LIF on tumor necrosis factor-alpha-induced apoptosis of oligodendrocytes. In conclusion, our data demonstrate that peripheral and CNS-infiltrating T cells from MS patients produce LIF, a protective factor for oligodendrocytes. This study emphasizes that secretion of LIF may contribute to the neuroprotective effects of autoreactive T cells.

Fc receptors and the common gamma-chain in experimental autoimmune encephalomyelitis

Fcgamma receptors (FcgammaRs), composed of a ligand-binding alpha-chain (FcRalpha) sometimes associated with the homodimeric, cell-signaling common gamma-chain (FcRgamma), comprise an important family of effector molecules linking humoral and cell-mediated adaptive immunity and regulating innate immunity. In peripheral autoimmune diseases, FcgammaRs contribute to inflammation and tissue damage through inappropriate activation of macrophages and neutrophils, release of cytokines and oxidants, and destruction of autoantibody-opsonized cells. In the central nervous system (CNS), the role of FcgammaRs in autoimmune disease such as multiple sclerosis (MS) remains largely unexplored despite extensive documentation of CNS-specific antibodies in cerebrospinal fluid and plaques. Several studies have now examined the role of FcgammaRs in experimental autoimmune encephalomyelitis (EAE), the animal model for MS, using mice genetically deficient in one or more FcgammaRs or in FcRgamma. These studies indicate that none of the FcgammaR alpha-chains are critical for EAE development and progression. In contrast, it is unequivocal that FcRgamma contributes to EAE, and surprisingly it seems that this effect is independent of FcgammaRs. Recent studies now indicate that FcRgamma expression in gammadelta T cells, most likely as a component of the TCR/CD3 signaling complex, is a critical requirement for EAE development. These studies support previous evidence implicating a pathogenic role for gammadelta T cells in EAE.

A 40-cM region on chromosome 14 plays a critical role in the development of virus persistence, demyelination, brain pathology and neurologic deficits in a murine viral model of multiple sclerosis

Theiler virus persists and induces immune-mediated demyelination in susceptible mice and serves as a model of multiple sclerosis. Previously, we identified 4 markers--D14Mit54, D14Mit60, D14Mit61, and D14Mit90--in a 40-cM region of chromosome 14 that are associated with demyelination in a cross between susceptible DBA/2 and resistant B10.D2 mice. We generated congenic-inbred mice to examine the contribution of this 40-cM region to disease. DBA Chr.14B10 mice, containing the chromosomal segment marked by the microsatellite polymorphisms, developed less spinal cord demyelination than did DBA/2 mice. More demyelination was found in the reciprocal congenic mouse B10.D2 Chr.14D2 than in the B10.D2 strain. Introduction of the DBA/2 chromosomal region onto the B10.D2 genetic background resulted in more severe disease in the striatum and cortex relative to B10.D2 mice. The importance of the marked region of chromosome 14 is indicated by the decrease in neurological performance using the Rotarod test during chronic disease in B10.D2 Chr.14D2 mice in comparison to B10.D2 mice. Viral replication was increased in B10.D2 Chr.14D2 mice as determined by quantitative real-time RT-PCR. These results indicate that the 40-cM region on chromosome 14 of DBA/2 mice contributes to viral persistence, subsequent demyelination, and loss of neurological function.

Study of Herpesvirus saimiri immortalization of gammadelta T cells derived from peripheral blood and CSF of multiple sclerosis patients

Human gammadelta T cells are an integral part of the innate immune system and have been difficult to study owing primarily to their relatively low abundance and their fastidious culture properties associated with short in vitro lifespan. Their increased presence within multiple sclerosis (MS) white matter plaques compared to peripheral blood (PB) suggests a specific interaction with central nervous system (CNS) tissues. This fact, together with their innate ability to lyse human oligodendrocytes in culture implicate them possibly in the pathogenesis of MS. To further investigate their potential role in MS, we studied whether gammadelta T cells could be effectively immortalized using Herpesvirus saimiri (HVS), so that they could be studied in longer-term cultures. Effective culture conditions were established resulting in efficient HVS growth transformation of multiple PB and CSF gammadelta T cell lines and clones that could exist in IL-2-dependent culture for periods in excess of 2 years. Phenotypic and functional comparison studies with parental nontransformed gammadelta T cells were performed to characterize the changes that possibly induced by viral transformation. Using panels of transformed gammadelta T cell clones representing discrete gammadelta TcR subtypes, there was no apparent correlation between intracytoplasmic cytokine expression or tumor cell cytotoxicity with a specific TcR. All transformed gammadelta T cells analyzed, regardless of their compartment of origin, strongly expressed intracytoplasmic IFN-gamma and TNF-alpha, but little IL-2 or anti-inflammatory IL-4 or IL-10. These results indicate that HVS transformation of gammadelta T cells can be used to generate lines and clones from both the CSF and PB compartments for further study and elucidation of their potential role in MS pathogenesis.

Role of gamma/delta T cell receptor-expressing lymphocytes in cutaneous infection caused by Staphylococcus aureus

The high number of gamma/delta-expressing T cells found in the epithelial lining layer suggests that they form a first line of defence against invading pathogens. To evaluate the role of gamma/delta T cell-receptor (TCR)-expressing cells in cutaneous infection caused by Staphylococcus aureus, mice lacking gamma/delta-expressing T cells (TCRdelta-/-) were inoculated intradermally with S. aureus, and compared with S. aureus-infected congeneic TCRdelta+/- control mice. The number of bacteria recovered from the skin of TCRdelta-/- mice was significantly higher (P = 0.0071) at early time-points after inoculation compared to the number of bacteria isolated from infected TCRdelta+/- congeneic controls. Nevertheless, inflammatory responses measured as serum IL-6 levels, were significantly lower in TCRdelta-/- mice than in the control group. A possible explanation for this discrepancy was the observation of significantly decreased overall numbers of infiltrating cutaneous T lymphocytes, which are important producers of IL-6. These results support the notion that the gamma/delta-expressing T cells that reside at the epithelial lining layer of the skin is of importance for early containment of the bacteria, thereby limiting their replication and spread.

gamma/delta T cells in multiple sclerosis: chemokine and chemokine receptor expression

gamma/delta T cells are enriched in multiple sclerosis (MS) brain lesions and have been postulated to contribute to the pathogenesis of the disease. Increased expression of the chemokine receptors CCR5 and CXCR3 on T cells and raised amounts of the chemokines RANTES and IP-10 have been noted in the CSF and brain tissue of MS patients, but the contribution of gamma delta T cells to these increases is unknown. We therefore compared intracellular RANTES and IP-10 production as well as CCR5, CXCR3, and CXCR1 expression by gamma delta T cells derived from the blood and CSF of patients with MS and healthy controls (HC). We observed higher RANTES production by MS gamma delta than by alpha beta T cell lines. Most of the MS as well as the HC gamma delta and alpha beta T cell lines expressed CXCR3, while expression of CXCR1 was low. Interestingly, MS gamma delta T cell lines, compared to lines from HC, expressed lower levels of CCR5. Furthermore, CSF-derived gamma delta T cells had even lower CCR5 expression than blood-derived ones. The higher RANTES production by MS gamma delta T cell lines, together with a lower expression of CCR5, may reflect an autoregulatory loop, caused by an increased production of its ligands (RANTES, MIP-1 alpha, and MIP-1 beta) or due to other pro-inflammatory cytokines. Alternatively, we show that lower CCR5 expression could also reflect the result of repeated in vivo stimulation of gamma delta T cells by autoantigens.

Granule-dependent cytolysis of Mycobacterium tuberculosis-infected macrophages by human gammadelta+ T cells has no effect on intracellular mycobacterial viability

One of the most important effector functions of activated gammadelta+ T cells in tuberculosis is their strong cytolytic activity against a variety of target cells, including M. tuberculosis-infected macrophages. In the present study, we investigated the relationship between the mechanism of cytolysis utilized by gammadelta+ CTL and intracellular M. tuberculosis survival using a panel of cytolytic human M. tuberculosis-specific gammadelta+ CTL clones. Cytolysis mediated by the gammadelta+ T-cell clones was found to be Ca2+-dependent, sensitive to Cyclosporin A, and was completely abrogated following Sr2+-induced de-granulation of the gammadelta+ T cell effectors. These data demonstrate that gammadelta+ T-cell-mediated cytoxicity was mediated via the granule exocytosis/perforin pathway. Despite significant cytolytic activity against mycobacteria infected U937 cells, the gammadelta+ CTL clones had no impact on the survival of intracellular M. tuberculosis.

Oligodendroglial apoptosis occurs along degenerating axons and is associated with FAS and p75 expression following spinal cord injury in the rat

Apoptosis or programmed cell death has been reported after CNS trauma. However, the significance of this mechanism in the pathophysiology of spinal cord injury, in particular at the cervical level, requires further investigation. In the present study, we used the extradural clip compression model in the rat to examine the cellular distribution of apoptosis following cervical spinal cord injury, the relationship between glial apoptosis and post-traumatic axonal degeneration and the possible role of apo[apoptosis]-1, CD95 (FAS) and p75 in initiating post-traumatic glial apoptosis. In situ terminal-deoxy-transferase mediated dUTP nick end labeling revealed apoptotic cells, largely oligodendrocytes as identified by cell specific markers, in grey and white matter following spinal cord injury. Apoptotic cell death was confirmed using electron microscopy and by the demonstration of DNA laddering on agarose gel electrophoresis. Beta-amyloid precursor protein was used as a molecular marker of axonal degeneration on western blots and immunohistochemistry. Degeneration of axons was temporally and spatially co-localized with glial apoptosis. FAS and p75 protein expression was seen in astrocytes, oligodendrocytes and microglia, and was also seen in some apoptotic glia after cord injury. Both FAS and p75 increased in expression in a temporal course, which mirrored the development of cellular apoptosis. The downstream caspases 3 and 8, which are linked to FAS and p75, demonstrated activation at times of maximal apoptosis, while FLIP-L an inhibitor of caspase 8, decreased at times of maximal apoptosis. We conclude that axonal degeneration after traumatic spinal cord injury is associated with glial, in particular oligodendroglial, apoptosis. Activation of the FAS and p75 death receptor pathways may be involved in initiating this process.

Structural dynamics of oligodendrocyte lysis by perforin in culture: relevance to multiple sclerosis

The mechanism by which oligodendrocytes are depleted from active lesions in multiple sclerosis (MS) is not clear but many reports implicate a cytolytic process. The most applied animal model for MS, chronic relapsing experimental autoimmune encephalomyelitis (EAE), has been established in inbred strains of mice, especially SJL and PL. Studies on oligodendrocytes from these strains in vitro have been hampered to date by an inability to grow these cells from mouse CNS tissue. We report here a successful method to culture SJL mouse oligodendrocytes and have analyzed lysis of these cells in vitro mediated by the pore-forming protein, perforin, a candidate effector molecule in inflammatory demyelination. Cultures were exposed to murine perforin, 36-72 hemolytic U, for up to 2.5 hr and examined using the oligodendrocyte phenotypic markers O4, galactocerebroside and myelin basic protein (MBP), in addition to a membrane dye (DiI) and a marker of necrosis, propidium iodide, (PI). Cultures were imaged chronologically by phase contrast, immunofluorescence, digital, light and electron microscopy. Findings showed that the majority of oligodendrocytes were killed within 60-90 min via pore expansion and ultimately, membrane disruption. The structural features of the cellular damage comprised swelling of the cell body, fenestration and fragmentation of membranes and processes, cytoplasmic vacuolation and breakdown of the nuclear envelope. Astrocytes in the same system were relatively resistant to cell lysis. The above patterns of oligodendrocyte damage in SJL oligodendrocytes were reminiscent of patterns in the MS lesion, leaving us to conclude that perforin may play an important role in the human disease.

Mechanisms of tissue injury in multiple sclerosis: opportunities for neuroprotective therapy

Development of neuroprotective therapies for multiple sclerosis is dependent on defining the precise mechanisms whereby immune effector cells and molecules are able to induce relatively selective injury of oligodendrocytes (OLs) and their myelin membranes. The selectivity of this injury could be conferred either by the properties of the effectors or the targets. The former would involve antigen specific recognition by either antibody or T cell receptor of the adaptive immune system. OLs are also susceptible to non antigen restricted injury mediated by components of the innate immune system including macrophages/microglia and NK cells. Target related selectivity could reflect the expression of death inducing surface receptors (such as Fas or TNFR-1) required for interaction with effector mediators and subsequent intracellular signaling pathways, including the caspase cascade. Development of therapeutic delivery systems, which would reach the site of disease activity within the CNS, will permit the administration of inhibitors either of the cell death pathway or of effector target interaction and opens new avenues to neuroprotection approach.

Downmodulation of the inflammatory response to bacterial infection by gammadelta T cells cytotoxic for activated macrophages

Although gammadelta T cells are involved in the regulation of inflammation after infection, their precise function is not known. Intraperitoneal infection of T cell receptor (TCR)-delta(-/-) mice with the intracellular bacterium Listeria monocytogenes resulted in the development of necrotic foci in the livers. In contrast, the peritoneal cavities of infected TCR-delta(-/-) mice contained an accumulation of low density activated macrophages and a reduced percentage of macrophages undergoing apoptosis. gammadelta T cell hybridomas derived from mice infected with Listeria were preferentially stimulated by low density macrophages from peritoneal exudates of infected mice. Furthermore, primary splenic gammadelta T cells isolated from Listeria-infected mice were cytotoxic for low density macrophages in vitro, and cytotoxicity was inhibited in the presence of antibodies to the gammadelta TCR. These results demonstrate a novel interaction between gammadelta T cells and activated macrophages in which gammadelta T cells are stimulated by terminally differentiated macrophages to acquire cytotoxic activity and which, in turn, induce macrophage cell death. This interaction suggests that gammadelta T cells regulate the inflammatory response to infection with intracellular pathogens by eliminating activated macrophages at the termination of the response.

Multiple sclerosis and central nervous system demyelination

Multiple sclerosis (MS) is characterized by multifocal areas within the CNS of demyelination with relative but not absolute axonal sparing. Initial lesion development appears dependent on T cell infiltration into the CNS; however, lesion expansion may reflect tissue injury induced by additional effector mechanisms derived from cells of the immune system and endogenous CNS cells (glial cells). This relative susceptibility to injury in MS of myelin and its cell of origin, the oligodendrocyte (OL), could reflect either the properties of the effectors or the targets. Effector-determined susceptibility could relate to presence of OL/myelin-restricted T cells or antibody. OLs, at least in vitro, express MHC class I molecules and are susceptible to CD8(+)T cell-mediated cytotoxicity. OL/myelin-specific antibodies are identified in MS lesions and could induce injury via complement- or ADCC-dependent mechanisms. OLs are susceptible to injury-mediated by non-specific cell effectors including NK cells, NK-like T cells (CD56(+)), and gamma/delta T cells via perforin/granzyme-dependent mechanisms. In vitro studies of OL injury mediated via tumor necrosis factor (TNF) and CD95 indicate that differential glial cell susceptibility to injury can depend on cell surface receptor expression and intracellular signaling pathways that are activated. These target-determined susceptibility factors may be amenable to neuroprotective therapies.

High numbers of perforin mRNA expressing CSF cells in multiple sclerosis patients with gadolinium-enhancing brain MRI lesions

Enhanced expression of pro- and anti-inflammatory cytokines is a common finding in MS, but attempts to correlate cytokine expression with disease activity have produced conflicting results. In this paper, gadolinium-(Gd-)enhancing lesions on brain MRI were used as markers for active inflammation in patients with MS not treated with any immunomodulatory drugs. In parallel, in situ hybridization was used to detect blood and cerebrospinal fluid (CSF) mononuclear cells (MNC) expressing cytokine mRNA. An association was observed between numbers of perforin mRNA expressing CSF MNC and numbers of Gd-enhancing brain MRI lesions. Perforin mRNA expressing CSF MNC were not detected in any of the patients lacking active lesions on brain MRI. The expression of tumor necrosis factor-alpha, interleukin-10 (IL-10) and IL-12 mRNA in CSF MNC did not differ between MS patients with and without active MRI lesions. Based on the present finding, a role for perforin in the disruption of the blood-brain barrier in MS can be hypothesized.

Immunopathogenesis of multiple sclerosis: the role of T cells

Multiple sclerosis is considered to be an autoimmune disease that results from aberrant immune responses to central nervous system antigens. T cells are considered to be crucial in orchestrating an immunopathological cascade that culminates in damage to the myelin sheath, oligodendrocytes and axons.