Abdelhadi Saoudi

CD40Ig treatment results in allograft acceptance mediated by CD8+CD45RClow T cells, IFN-γ, and indoleamine 2,3-dioxygenase

Treatment with CD40Ig results in indefinite allograft survival in a complete MHC-mismatched heart allograft model in the rat. Here we show that serial second, third, and fourth adoptive transfers of total splenocytes from CD40Ig-treated recipients into secondary recipients led to indefinite donor-specific allograft acceptance. Purification of splenocyte subpopulations from CD40Ig-treated recipients demonstrated that only the adoptively transferred CD8(+)CD45RC(low) subset resulted in donor-specific long-term survival, whereas CD8(+)CD45RC(low) T cells from naive animals did not. Accepted grafts displayed increased indoleamine 2,3-dioxygenase (IDO) expression restricted in the graft to ECs. Coculture of donor ECs with CD8(+)CD45RC(low) T cells purified from CD40Ig-treated animals resulted in donor-specific IDO expression dependent on IFN-gamma. Neutralization of IFN-gamma or IDO triggered acute allograft rejection in both CD40Ig-treated and adoptively transferred recipients. This study demonstrates for what we believe to be the first time that interference in CD40-CD40 ligand (CD40-CD40L) interactions induces allospecific CD8(+) Tregs that maintain allograft survival. CD8(+)CD45RC(low) T cells act through IFN-gamma production, which in turn induces IDO expression by graft ECs. Thus, donor alloantigen-specific CD8(+) Tregs may promote local graft immune privilege through IDO expression.

Cutting Edge: Vα14-Jα281 NKT Cells Naturally Regulate Experimental Autoimmune Encephalomyelitis in Nonobese Diabetic Mice

Although deficiencies in the NKT cell population have been observed in multiple sclerosis and mouse strains susceptible to experimental autoimmune encephalomyelitis (EAE), little is known about the function of these cells in CNS autoimmunity. In this work we report that TCR Vα14-Jα281 transgenic nonobese diabetic mice, which are enriched in CD1d-restricted NKT cells, are protected from EAE. The protection is associated with a striking inhibition of Ag-specific IFN-γ production in the spleen, implying modulation of the encephalitogenic Th1 response. This modulation is independent of IL-4 because IL-4-deficient Vα14-Jα281 mice are still protected against EAE and independent of NKT cell-driven Th1 to Th2 deviation, because no increased autoantigen-specific Th2 response was observed in immunized Vα14-Jα281 transgenic mice. Our findings indicate that enrichment and/or stimulation of CD1d-dependent NKT cells may be used as a novel strategy to treat CNS autoimmunity.

Estrogen Enhances Susceptibility to Experimental Autoimmune Myasthenia Gravis by Promoting Type 1-Polarized Immune Responses

Myasthenia gravis (MG) is an organ-specific autoimmune disease caused in most cases by autoantibodies against the nicotinic acetylcholine receptor (AChR). It is now well documented that many autoimmune diseases, including MG, are more prevalent in women than in men, and that fluctuations in disease severity occur during pregnancy. These observations raise the question of the potential role of sex hormones, such as estrogens, as mediators of sex differences in autoimmunity. In the present study, we have analyzed the effect of 17β-estradiol (E2) on the pathogenesis of experimental autoimmune myasthenia gravis (EAMG), an animal model of MG. We show that treatment with E2 before Ag priming is necessary and sufficient to promote AChR-specific Th1 cell expansion in vivo. This time-limited exposure to E2 enhances the production of anti-AChR IgG2ab (specific for b allotype; e.g., B6) and IgG2b, but not IgG1, and significantly increases the severity of EAMG in mice. Interestingly, the E2-mediated augmentation in AChR-specific Th1 response correlates with an enhanced production of IL-12 by splenic APCs through the recruitment of CD8α+ dendritic cells. These data provide the first evidence that estrogen enhances EAMG, and sheds some light on the role of sex hormones in immune responses and susceptibility to autoimmune disease in women.

Cellular and genetic factors involved in the difference between Brown Norway and Lewis rats to develop respectively type‐2 and type‐1 immune‐mediated diseases

Summary: The understanding of the mechanisms of immune tolerance and the unravelling of the pathophysiology of autoimmune diseases rely on animal models. In this respect, BN and LEW rats represent models of choice to study immune‐mediated diseases from the cellular and genetic points of view. Indeed, BN and LEW rats are extremes with respect to their polarisation of the immune response as well as their susceptibility to autoimmune diseases. LEW rats are susceptible to Th1‐mediated autoimmune diseases while BN rats are highly susceptible to Th2‐mediated autoimmune disease. Comparison of the T cell compartment between LEW and BN rats revealed several important differences. 1) A MHC‐dependent quantitative difference that is due to a defect in the CD8 T cell compartment in BN rats. 2) A qualitative MHC‐independent difference that is related to a high frequency of CD45RClow CD4 and CD8 T cell subsets, producing IL‐4, IL‐13, IL‐10 and TGF‐β in BN rats as compared to LEW rats. 3) Interestingly, the genetic studies showed that susceptibility to Th1‐mediated experimental autoimmune encephalomyelitis, and to Th2‐mediated disorders triggered by gold salts as well as the difference in the CD45RChigh/CD45RClow ratio between LEW and BN rats are genetically determined by regions on chromosomes 9, 10 and 20.

Alloreactive CD4 T lymphocytes responsible for acute and chronic graft‐versus‐host disease are contained within the CD45RChigh but not the CD45RClow subset

Graft‐versus‐host disease (GvHD) is a major complication of allogeneic bone marrow transplantation and occurs when donor T cells react with histo‐incompatible recipients antigens. In thepresent study, we analyzed the contribution of CD4 T cell subsets, defined according to their CD45RC expression level, in the development of acute and chronic GvHD. For this purpose, we used the model of GvHD induced in rats when parental lymphocytes are transferred to irradiated (LEW×BN) F1 hybrid recipients. We showed that parental CD45RChigh (naive cells) CD4 T cells induced both acute and chronic GvHD while CD45RClow (memory cells) subset did not. In vitro, only CD45RChigh CD4 T cells proliferated and produced cytokines in response to alloantigen stimulation. LEW and BN CD45RChigh CD4 T cells produced different cytokine profiles in response to in vitro allostimulation, which could explain their ability to induce different forms of GvHD. Finally, we showed that memory CD45RClow CD4 T cells, known to contain regulatory T cells, were unable to prevent GvHD induction. Together these data show that memory CD45RClow CD4 T cells do not contain functional alloreactive T cells and suggest that selective transfusion of donor memory cells could greatly improve post‐transplant immune reconstitution without riskof GvHD induction.

Role of IFNγ in Allograft Tolerance Mediated by CD4+CD25+ Regulatory T Cells by Induction of IDO in Endothelial Cells

Regulatory T cells have been described to specifically accumulate at the site of regulation together with effector T cells and antigen‐presenting cells, establishing a state of local immune privilege. However the mechanisms of this interplay remain to be defined. We previously demonstrated, in a fully MHC mismatched rat cardiac allograft combination, that a short‐term treatment with a deoxyspergualine analogue, LF15‐0195, induces long‐term allograft tolerance with a specific expansion of regulatory CD4+CD25+T cells that accumulate within the graft. In this study, we show that following transfer of regulatory CD4+T cells to a secondary irradiated recipient, regulatory CD25+Foxp3+ and CD25+Foxp3− CD4+T cells accumulate at the graft site and induce graft endothelial cell expression of Indoleamine 2, 3‐dioxygenase (IDO) by an IFNγ‐dependent mechanism. Moreover, in vivo transfer of tolerance can be abrogated by blocking IFNγ or IDO, and anti‐IFNγ reduces the survival/expansion of alloantigen‐induced regulatory Foxp3+CD4+T cells. Together, our results demonstrate interrelated mechanisms between regulatory CD4+CD25+T cells and the graft endothelial cells in this local immune privilege, and a key role for IFNγ and IDO in this process.

Tyrosine kinase 2 variant influences T lymphocyte polarization and multiple sclerosis susceptibility

The tyrosine kinase 2 variant rs34536443 has been established as a genetic risk factor for multiple sclerosis in a variety of populations. However, the functional effect of this variant on disease pathogenesis remains unclear. This study replicated the genetic association of tyrosine kinase 2 with multiple sclerosis in a cohort of 1366 French patients and 1802 controls. Furthermore, we assessed the functional consequences of this polymorphism on human T lymphocytes by comparing the reactivity and cytokine profile of T lymphocytes isolated from individuals expressing the protective TYK2(GC) genotype with the disease-associated TYK2(GG) genotype. Our results demonstrate that the protective C allele infers decreased tyrosine kinase 2 activity, and this reduction of activity is associated with a shift in the cytokine profile favouring the secretion of Th2 cytokines. These findings suggest that the rs34536443 variant effect on multiple sclerosis susceptibility might be mediated by deviating T lymphocyte differentiation toward a Th2 phenotype. This impact of tyrosine kinase 2 on effector differentiation is likely to be of wider importance because other autoimmune diseases also have been associated with polymorphisms within tyrosine kinase 2. The modulation of tyrosine kinase 2 activity might therefore represent a new therapeutic approach for the treatment of autoimmune diseases.

Dihydropyridine Receptors Are Selective Markers of Th2 Cells and Can Be Targeted to Prevent Th2-Dependent Immunopathological Disorders

Th1 cells that produce IFN-γ are essential in the elimination of intracellular pathogens, and Th2 cells that synthetize IL-4 control the eradication of helminths. However, highly polarized Th1 or Th2 responses may be harmful and even lethal. Thus, the development of strategies to selectively down-modulate Th1 or Th2 responses is of therapeutic importance. Herein, we demonstrate that dihydropyridine receptors (DHPR) are expressed on Th2 and not on Th1 murine cells. By using selective agonists and antagonists of DHPR, we show that DHPR are involved in TCR-dependent calcium response in Th2 cells as well as in IL-4, IL-5, and IL-10 synthesis. Nicardipine, an inhibitor of DHPR, is beneficial in experimental models of Th2-dependent pathologies in rats. It strongly inhibits the Th2-mediated autoimmune glomerulonephritis induced by injecting Brown Norway (BN) rats with heavy metals. This drug also prevents the chronic graft vs host reaction induced by injecting CD4+ T cells from BN rats into (LEW × BN)F1 hybrids. By contrast, treatment with nicardipine has no effect on the Th1-dependent experimental autoimmune encephalomyelitis triggered in LEW rats immunized with myelin. These data indicate that 1) DHPR are a selective marker of Th2 cells, 2) these calcium channels contribute to calcium signaling in Th2 cells, and 3) blockers of these channels are beneficial in the treatment of Th2-mediated pathologies.

A Role for VAV1 in Experimental Autoimmune Encephalomyelitis and Multiple Sclerosis

VAV1 plays a role in regulating proinflammatory cytokines, which underlie the susceptibility for developing experimental autoimmune encephalomyelitis and multiple sclerosis. Rat Genetics Moving Up Multiple sclerosis (MS) is a common autoimmune disease with a complex etiology that attacks the brain and spinal cord and emerges as a result from both genetic and environmental factors. At present, there is no predictive biomarker for MS and no cure for adults who present with the disease, and only a few genes have been unambiguously linked to its development. The hunt has been to address these challenges, but also to uncover new targets that are associated with a high susceptibility for MS to augment disease-modifying treatments that are in clinical use. Using experimental autoimmune encephalomyelitis, an animal model of MS, Jagodic et al. have focused on a region of the rat genome on chromosome 9 that encodes the gene Vav1. Although this gene was initially identified as an oncogene, it later was found to be an important signal transducer with a pivotal role in immune cells, the very first hint being its specific activation after T cell receptor stimulation. The authors show that a specific mutation identified in rat Vav1 altered Vav1 protein abundances, immune cell activation, and neuroinflammation induction. Taking this observation a step further, among 12,735 individuals of European descent, Jagodic et al. reveal an association between a set of common variants within the first intron of VAV1 and susceptibility for MS. Like what they observed in the rat, common VAV1 variants altered VAV1 expression and immune activation in the peripheral blood and in the cerebrospinal fluid cells of MS patients. This study displays the power of using rat genetics to encourage the discovery of human genetic targets in common diseases such as MS. Multiple sclerosis, the most common cause of progressive neurological disability in young adults, is a chronic inflammatory disease. There is solid evidence for a genetic influence in multiple sclerosis, and deciphering the causative genes could reveal key pathways influencing the disease. A genome region on rat chromosome 9 regulates experimental autoimmune encephalomyelitis, a model for multiple sclerosis. Using interval-specific congenic rat lines and association of single-nucleotide polymorphisms with inflammatory phenotypes, we localized the gene of influence to Vav1, which codes for a signal-transducing protein in leukocytes. Analysis of seven human cohorts (12,735 individuals) demonstrated an association of rs2546133-rs2617822 haplotypes in the first VAV1 intron with multiple sclerosis (CA: odds ratio, 1.18; CG: odds ratio, 0.86; TG: odds ratio, 0.90). The risk CA haplotype also predisposed for higher VAV1 messenger RNA expression. VAV1 expression was increased in individuals with multiple sclerosis and correlated with tumor necrosis factor and interferon-γ expression in peripheral blood and cerebrospinal fluid cells. We conclude that VAV1 plays a central role in controlling central nervous system immune-mediated disease and proinflammatory cytokine production critical for disease pathogenesis.

The Balance Between CD45RChigh and CD45RClow CD4 T Cells in Rats Is Intrinsic to Bone Marrow-Derived Cells and Is Genetically Controlled

The level of CD45RC expression differentiates rat CD4 T cells in two subpopulations, CD45RChigh and CD45RClow, that have different cytokine profiles and functions. Interestingly, Lewis (LEW) and Brown Norway (BN) rats, two strains that differ in their ability to mount type 1 and type 2 immune responses and in their susceptibility to autoimmune diseases, exhibit distinct CD45RChigh/CD45RClow CD4 T cell ratios. The CD45RChigh subpopulation predominates in LEW rats, and the CD45RClow subpopulation in BN rats. In this study, we found that the antiinflammatory cytokines, IL-4, IL-10, and IL-13, are exclusively produced by the CD45RClow CD4 T cells. Using bone marrow chimeras, we showed that the difference in the CD45RChigh/CD45RClow CD4 T cell ratio between naive LEW and BN rats is intrinsic to hemopoietic cells. Furthermore, a genome-wide search for loci controlling the balance between T cell subpopulations was conducted in a (LEW × BN) F2 intercross. Genome scanning identified one quantitative trait locus on chromosome 9 (∼17 centiMorgan (cM); log of the odds ratio (LOD) score 3.9). In addition, two regions on chromosomes 10 (∼28 cM; LOD score 3.1) and 20 (∼40 cM; LOD ratio score 3) that contain, respectively, a cytokine gene cluster and the MHC region were suggestive for linkage. Interestingly, overlapping regions on these chromosomes have been implicated in the susceptibility to various immune-mediated disorders. The identification and functional characterization of genes in these regions controlling the CD45RChigh/CD45RClow Th cell subpopulations may shed light on key regulatory mechanisms of pathogenic immune responses.