Sylvie Fournier

B7 Expression on T Cells Down-Regulates Immune Responses through CTLA-4 Ligation via R-T Interactions

Although B7 on APCs has a well-recognized role in T cell costimulation, little is known about the functional significance of constitutive and activation-induced B7 expression that also occurs on T cells. To analyze the role of B7 on T cells, B7-1/B7-2-deficient mice (B7 double knockout) and mice overexpressing B7-2 exclusively on T cells (B7-2 transgenic) were used as T cell donors for allogeneic transplant recipients, and graft-vs-host disease (GVHD) was assessed. B7 double-knockout T cells resulted in significant GVHD acceleration compared with wild-type T cells. Conversely, B7-2 transgenic donor T cells mediated reduced GVHD mortality compared with wild-type T cells. Data indicated that B7 expression on T cells down-regulated alloresponses through CTLA-4 ligation. This study is the first to provide definitive in vivo data illustrating the importance of T cell-associated B7 as a negative regulator of immune responses in a clinically relevant murine model of GVHD. The up-regulation of B7 on T cells may be an important component of normal immune homeostasis.

Characterization of relapsing-remitting and chronic forms of experimental autoimmune encephalomyelitis in C57BL/6 mice.

Multiple sclerosis (MS) is an autoimmune, demyelinating disease of the central nervous system (CNS). Like MS, the animal model experimental autoimmune encephalomyelitis (EAE) is characterized by CNS inflammation and demyelination and can follow a relapsing–remitting (RR) or chronic (CH) disease course. The molecular and pathological differences that underlie these different forms of EAE are not fully understood. We have compared the differences in RR‐ and CH‐EAE generated in the same mouse strain (C57BL/6) using the same antigen. At the peak of disease when mice in both groups have similar clinical scores, CH‐EAE is associated with increased lesion burden, myelin loss, axonal damage, and chemokine/cytokine expression when compared with RR‐EAE. We further showed that inflammation and myelin loss continue to worsen in later stages of CH‐EAE, whereas these features are largely resolved at the equivalent stage in RR‐EAE. Additionally, axonal loss at these later stages is more severe in CH‐EAE than in RR‐EAE. We also demonstrated that CH‐EAE is associated with a greater predominance of CD8+ T cells in the CNS that exhibit MOG35–55 antigen specificity. These studies therefore showed that, as early as the peak stage of disease, RR‐ and CH‐EAE differ remarkably in their immune cell profile, chemokine/cytokine responses, and histopathological features. These data also indicated that this model of CH‐EAE exhibits pathological features of a chronic‐progressive disease profile and suggested that the sustained chronic phenotype is due to a combination of axonal loss, myelin loss, and continuing inflammation.

Constitutive expression of a costimulatory ligand on antigen-presenting cells in the nervous system drives demyelinating disease

It has been proposed that the activation status of antigen‐presenting cells (APCs) plays a significant role in the development of autoimmune disease. Whether expression of costimulatory ligands on tissue‐resident APCs controls organ‐specific autoimmune responses has not been tested. We here report that transgenic mice constitutively expressing the costimulatory ligand B7.2/CD86 on microglia in the central nervous system (CNS) and on related cells in the proximal peripheral nervous tissue spontaneously develop autoimmune demyelinating disease. Disease‐affected nervous tissue in transgenic mice showed infiltration characterized by a predominance of CD8+ memory‐effector T cells, as well as CD4+ T cells. Transgenic animals lacking αβ TCR+ T cells were completely resistant to disease development. Transgenic T cells induced disease when adoptively transferred into T cell‐deficient B7.2 transgenic recipients but not into non‐transgenic recipients. These data provide evidence that B7/CD28 interactions within the nervous tissue are critical determinants of disease development. Our findings have important implications for understanding the etiology of nervous system autoimmune diseases such as multiple sclerosis (MS) and Guillain‐Barré syndrome (GBS).

A Pathogenic Role for CD8+ T Cells in a Spontaneous Model of Demyelinating Disease

Transgenic (Tg) mice that overexpress the costimulatory ligand B7.2/CD86 on microglia spontaneously develop a T cell-mediated demyelinating disease. Characterization of the inflammatory infiltrates in the nervous tissue revealed a predominance of CD8+ T cells, suggesting a prominent role of this T cell subset in the pathology. In this study, we show that the same neurological disease occurred in Tg mice deficient in the generation of CD4+ T cells, with an earlier time of onset. Analysis of the CD8+ T cell repertoire at early stage of disease revealed the presence of selected clonal expansions in the CNS but not in peripheral lymphoid organs. We further show that Tg animals deficient in IFN-γ receptor expression were completely resistant to disease development. Microglia activation that is an early event in disease development is IFN-γ dependent and thus appears as a key element in disease pathogenesis. Collectively, our data indicate that the spontaneous demyelinating disease in this animal model occurs as a consequence of an inflammatory response initiated through the activation of CNS-specific CD8+ T cells by Tg expression of B7.2 within the target organ. Thus, autoreactive CD8+ T cells can contribute directly to the pathogenesis of neuroinflammatory diseases such as multiple sclerosis.

Immunization with an Apoptotic Cell-Binding Protein Recapitulates the Nephritis and Sequential Autoantibody Emergence of Systemic Lupus Erythematosus

The initial events predisposing to loss of tolerance in patients with systemic lupus erythematosus (SLE) are largely unknown, as are the events that precipitate the transition from preclinical to overt disease. We hypothesized that induction of murine SLE would require tipping the balance between tolerance and immunity in two ways: 1) an immunogen that could take advantage of apoptotic cells as a scaffold for epitope spread, and 2) an immune activator that would generate a strong and persistent T cell response to the inciting immunogen. We show that immunization of C57BL/6 and BALB/c mice with human β2-glycoprotein I, an apoptotic cell-binding protein, in the presence of LPS induces a long-lived, potent response to β2-glycoprotein I that results in epitope spread to multiple SLE autoantigens. SLE-specific autoantibodies emerged in a sequential manner that recapitulated the order seen in human SLE. Moreover, immunized mice developed overt glomerulonephritis closely resembling human lupus nephritis.

Transgenic Mice Expressing the p75 CCAAT-Displacement Protein/Cut Homeobox Isoform Develop a Myeloproliferative Disease–Like Myeloid Leukemia

The p75 CCAAT-displacement protein/Cut homeobox (CDP/Cux) isoform was previously reported to be overexpressed in human breast cancers. To investigate its oncogenic potential, we engineered two transgenic mouse lines expressing p75 CDP/Cux under the control of the mouse mammary tumor virus-long terminal repeat. The FVB strain of mouse is generally used in the generation of mouse models for breast cancer. The transgene was introduced into the hprt locus of 129/Ola embryonic stem cells and, following germ line passage, was backcrossed onto the FVB and C57BL/6 mouse strains. Here, we describe the phenotype of p75 CDP/Cux transgenic virgin female mice of the first backcross generations. We report that after a long latency period, approximately 33% of mice from two independent transgenic lines and from backcrosses into either the FVB or the C57BL/6 strains succumbed to a similar disease characterized by splenomegaly, hepatomegaly, and frequent infiltration of leukocytes into nonhematopoietic organs like the kidneys and lungs. Although an excess of B or T cells was observed in three diseased mice, in 17 other cases, histologic and flow cytometry analyses revealed the expansion of a population of neutrophils in the blood, spleen, and bone marrow. The increase in neutrophils correlated with signs of anemia and thrombocytopenia, whereas there was no indication of a reactive process. Therefore, p75 CDP/Cux transgenic mice displayed heightened susceptibility to a disease defined as a myeloproliferative disease-like myeloid leukemia. These results indicate that the overexpression of p75 CDP/Cux could alter homeostasis in the hematopoietic compartment.

Innate inflammatory responses to the Gram-positive bacterium Lactococcus lactis

Lactococcus lactis is a non-pathogenic and non-colonizing Gram-positive bacterium commonly used in the dairy industry. To support the potential applications of this bacterium, such as use as an oral live vaccine, it is of interest to investigate the adjuvant properties of L. lactis. We compared the proinflammatory effects of L. lactis with two non-pathogenic Gram-negative bacteria: Escherichia coli and Salmonella typhi, a widely studied live vaccine. The gene expression profiles of chemokines induced by the three bacteria were examined in macrophages in vitro and in cells recruited into murine air-pouches in vivo. In addition, we studied the effect of co-incubating bacteria with dendritic cells (DCs) generated from mice bone marrow. We demonstrate that L. lactis exhibits proinflammatory effects, which indicates a capacity for adjuvanticity by this bacterium.

Exploring the roles of CD8+ T lymphocytes in the pathogenesis of autoimmune demyelination

Multiple sclerosis (MS) is an autoimmune disease characterized by mononuclear cell infiltrates, focal demyelination, and the development of sclerotic plaques within the central nervous system. Although CD8+ T lymphocytes are more abundant than CD4+ T lymphocytes in MS lesions, the latter cell type has been most commonly implicated in the genesis of this disease. Recent evidence, however, suggests that both T cell populations and their various subsets are able to contribute to disease initiation and progression. To gain insight into disease mechanisms of potential relevance to MS, a variety of animal models have been developed. Foremost among these has been experimental autoimmune encephalomyelitis (EAE), a rodent model of MS induced by the immunization of genetically susceptible animals with peptides derived from myelin-associated proteins. While EAE has contributed greatly to our understanding of mechanisms involved in autoimmune demyelination, this model has been of limited use as far as shedding light on the possible contributions of CD8+ T lymphocytes to disease pathogenesis. Herein, we review evidence supporting a role for CD8+ T lymphocytes in both MS and EAE and also highlight several novel murine systems designed for investigating the role(s) of CD8+ T cells in autoimmune demyelination.

Impact of Leishmania mexicana Infection on Dendritic Cell Signaling and Functions

Leishmania parasites have the ability to modify macrophage signaling pathways in order to survive and multiply within its mammalian host. They are also known to invade other cells including neutrophils, fibroblasts and dendritic cells (DCs). DCs have an important role in immunity as the link between innate and adaptive immunity, necessary for the development of an effective response; however, the impact of Leishmania mexicana infection on DCs has been poorly studied. Herein, we report that Leishmania infection rapidly induced DC protein tyrosine phosphatases activity, leading to MAP kinases inactivation. In line with this, L. mexicana was found to decrease the nuclear translocation of transcription factors such as AP-1 and NF-κB. Concomitantly, L. mexicana-infected DCs showed reduced expression of several surface antigen-presenting and co-stimulatory molecules upon LPS stimulation. Leishmania-induced interference on DC maturation was further reflected by their reduced capacity to present OVA antigen to OVA-specific T cells, as shown by abrogation of IL-2 production by the T cells. Collectively, our data revealed that DC infection by L. mexicana appears to affect the cellular and immunological mechanisms necessary for the development of an effective and protective immune response, therefore favouring the survival and propagation of the parasite within its host.

A new animal model of spontaneous autoimmune peripheral polyneuropathy: implications for Guillain-Barré syndrome

BackgroundSpontaneous autoimmune peripheral neuropathy including Guillain-Barré Syndrome (GBS) represents as one of the serious emergencies in neurology. Although pathological changes have been well documented, molecular and cellular mechanisms of GBS are still under-explored, partially due to short of appropriate animal models. The field lacks of spontaneous and translatable models for mechanistic investigations. As GBS is preceded often by viral or bacterial infection, a condition can enhance co-stimulatory activity; we sought to investigate the critical role of T cell co-stimulation in this autoimmune disease.ResultsOur previous study reported that transgene-derived constitutive expression of co-stimulator B7.2 on antigen presenting cells of the nervous tissues drove spontaneous neurological disorders. Depletion of CD4+ T cells in L31 mice accelerated the onset and increased the prevalence of the disease. In the current study, we further demonstrated that L31/CD4-/- mice exhibited both motor and sensory deficits, including weakness and paresis of limbs, numbness to mechanical stimuli and hypersensitivity to thermal stimulation. Pathological changes were characterized by massive infiltration of macrophages and CD8+ T cells, demyelination and axonal damage in peripheral nerves, while changes in spinal cords could be secondary to the PNS damage. In symptomatic L31/CD4-/- mice, the disruption of the blood neural barriers was observed mainly in peripheral nerves. Interestingly, the infiltration of immune cells was initiated in pre-symptomatic L31/CD4-/- mice, prior to the disease onset, in the DRG and spinal roots where the blood nerve barrier is virtually absent.ConclusionsL31/CD4-/- mice mimic most parts of clinical and pathological signatures of GBS in human; thus providing an unconventional opportunity to experimentally explore the critical events that lead to spontaneous, autoimmune demyelinating disease of the peripheral nervous system.