A Defect in Lineage Fate Decision during Fetal Thymic Invariant NKT Cell Development May Regulate Susceptibility to Type 1 Diabetes

NKT and NKT-like Cells in Autoimmune Neuroinflammatory Diseases-Multiple Sclerosis, Myasthenia Gravis and Guillain-Barre Syndrome

NKT cells comprise three subsets—type I (invariant, iNKT), type II, and NKT-like cells, of which iNKT cells are the most studied subset. They are capable of rapid cytokine production after the initial stimulus, thus they may be important for polarisation of Th cells. Due to this, they may be an important cell subset in autoimmune diseases. In the current review, we are summarising results of NKT-oriented studies in major neurological autoimmune diseases—multiple sclerosis, myasthenia gravis, and Guillain-Barre syndrome and their corresponding animal models.

Lineage divergence at the first TCR-dependent checkpoint: preferential γδ and impaired αβ T cell development in nonobese diabetic mice

The first TCR-dependent checkpoint in the thymus determines αβ versus γδ T lineage fate and sets the stage for later T cell differentiation decisions. We had previously shown that early T cells in NOD mice that are unable to rearrange a TCR exhibit a defect in checkpoint enforcement at this stage. To determine if T cell progenitors from wild-type NOD mice also exhibit cell-autonomous defects in development, we investigated their differentiation in the Notch-ligand-presenting OP9-DL1 coculture system, as well as by analysis of T cell development in vivo. Cultured CD4 and CD8 double-negative cells from NOD mice exhibited major defects in the generation of CD4 and CD8 double-positive αβ T cells, whereas γδ T cell development from bipotent precursors was enhanced. Limiting dilution and single-cell experiments show that the divergent effects on αβ and γδ T cell development did not spring from biased lineage choice but from increased proliferation of γδ T cells and impaired accumulation of αβ T lineage double-positive cells. In vivo, NOD early T cell subsets in the thymus also show characteristics indicative of defective β-selection, and peripheral αβ T cells are poorly established in mixed bone marrow chimeras, contrasting with strong γδ T as well as B cell repopulation. Thus, NOD T cell precursors reveal divergent, lineage-specific differentiation abnormalities in vitro and in vivo from the first TCR-dependent developmental choice point, which may have consequences for subsequent lineage decisions and effector functions.

A novel CD93 polymorphism in non-obese diabetic (NOD) and NZB/W F1 mice is linked to a CD4+ iNKT cell deficient state

In the present study, we characterize a polymorphism in the CD93 molecule, originally identified as the receptor for the C1q complement component (i.e., C1qRp, or AA4.1) in non-obese diabetic (NOD) mice. This allele carries a coding polymorphism in the first epidermal growth factor-like domain of CD93, which results in an amino acid substitution from Asn→His at position 264. This polymorphism does not appear to influence protein translation or ecto-domain cleavage, as CD93 is detectable in bone-marrow-derived macrophage and B-cell precursor lysates and in soluble form in the serum. The NOD CD93 isoform causes a phenotypic aberrancy in the early B-cell developmental stages (i.e., pro-, pre-, immature, and transitional), likely related to a conformational variation. Interestingly, the NZB/W F1 strain, which serves as a murine model of Lupus, also expresses an identical CD93 sequence polymorphism. Cd93 is located within the NOD Idd13 locus and is also tightly linked to the NZB/W F1 Wbw1 and Nkt2 disease susceptibility loci, which are thought to regulate natural killer T (NKT) cell homeostasis. Consistent with this genetic linkage, we found B6 CD93^−/− and B6.NOD^Idd13 mice to be susceptible to a profound CD4⁺ NKT cell deficient state. These data suggest that Cd93 may be an autoimmune susceptibility gene residing within the Idd13 locus, which plays a role in regulating absolute numbers of CD4⁺ NKT cells.

Clinical application of NKT cell biology in type I (autoimmune) diabetes mellitus

Type 1 natural killer T (NKT) cells are a population of CD1d-restricted, regulatory T cells that exhibit various NK cell characteristics and rapidly produce cytokines on stimulation with glycolipid antigen. In type I diabetes (TID), NKT cells are thought to have a tolerogenic function, evidenced by NKT cell numerical and functional deficiencies in the nonobese diabetic (NOD) mouse, which when corrected, can ameliorate disease. The mechanisms by which NKT cells can mediate their immunosuppressive effects in NOD mice are still poorly understood, which makes successful clinical translation of NKT- cell-based therapies challenging. However, new insights into the genetic control of NKT cell deficiencies have provided some understanding of the genes that may control NKT cell number and function, potentially offering a new avenue for assessing TID risk in humans. Here, we review the mechanisms by which NKT cells are thought to prevent TID, discuss the evidence for involvement of NKT cells in the regulation of human TID and examine the genetic control of NKT cell number and function. A greater understanding of these areas will increase the chances of successful clinical manipulation of NKT cells to prevent or treat TID.

Role of NKT cells in the digestive system. II. NKT cells and diabetes

Natural killer T (NKT) cells are a subset of regulatory T lymphocytes that recognize glycolipid antigens presented by the major histocompatibility complex class I-related glycoprotein CD1d. NKT cells have been implicated in regulating the progression of Type 1 diabetes (T1D) in human patients and in an animal model for T1D. In addition, glycolipid agonists of NKT cells have been successful in preventing diabetes in mice, raising enthusiasm for the development of NKT cell-based therapies for T1D.

Regulation of type 1 diabetes by NKT cells

Type 1 diabetes is an autoimmune disease due to the destruction of insulin-producing pancreatic beta cells. Natural Killer T (NKT) cells are a T-cell subset that links the innate and adaptive immune systems. NKT cells play a key regulatory role in type 1 diabetes. The absence of NKT cells correlates with exacerbation of type 1 diabetes, whereas an increased frequency and/or activation of NKT cells prevents beta-cell autoimmunity. Various mechanisms are involved in the protective effect of NKT cells. The goal is now to translate knowledge gained from mouse models into human therapeutics.

Reduced CD4+ subset and Th1 bias of the human iNKT cells in Type 1 diabetes mellitus

Invariant NKT (iNKT) cells are considered to be important in some autoimmune diseases including Type 1 diabetes mellitus (T1DM). So far, the published data are contradictory in regard to the role of iNKT cells in T1DM. We aimed to study iNKT cell frequency and the function of different iNKT cell subgroups in T1DM. We compared the results of four subject groups: healthy (H), long-term T2DM (ltT2DM; more than 1 year), newly diagnosed T1DM (ndT1DM; less than 3 months), and ltT1DM (more than 1 year) individuals. We measured the iNKT cell frequencies by costaining for the invariant TCR alpha-chain with 6B11-FITC and Valpha24-PE. After sorting the Valpha24+6B11+ cells, the generated iNKT clones were characterized. We tested CD4, CD8, and CD161 expression and IL-4 and IFN-gamma production on TCR stimulation. The CD4+ population among the iNKT cells was decreased significantly in ltT1DM versus ndT1DM, ltT2DM, or H individuals. The T1DM iNKT cell cytokine profile markedly shifted to the Th1 direction. There was no difference in the frequency of iNKT cells in PBMC among the different patient groups. The decrease in the CD4+ population among the iNKT cells and their Th1 shift indicates dysfunction of these potentially important regulatory cells in T1DM.

Invariant V(alpha)19i T cells regulate autoimmune inflammation

T cells expressing an invariant V(alpha)19-J(alpha)33 T cell receptor alpha-chain (V(alpha)19i TCR) are restricted by the nonpolymorphic major histocompatibility complex class Ib molecule MR1. Whether V(alpha)19i T cells are involved in autoimmunity is not understood. Here we demonstrate that T cells expressing the V(alpha)19i TCR transgene inhibited the induction and progression of experimental autoimmune encephalomyelitis (EAE), a mouse model of multiple sclerosis. Similarly, EAE was exacerbated in MR1-deficient mice, which lack V(alpha)19i T cells. EAE suppression was accompanied by reduced production of inflammatory mediators and increased secretion of interleukin 10. Interleukin 10 production occurred at least in part through interactions between B cells and V(alpha)19i T cells mediated by the ICOS costimulatory molecule. These results suggest an immunoregulatory function for V(alpha)19i T cells.

CD4+CD25+ Tregs and NKT cells: regulators regulating regulators

CD4+CD25+ regulatory T cells (Tregs) and natural killer T (NKT) cells are two populations of T lymphocytes that can independently regulate adaptive and innate immune responses. Although most studies have investigated the regulatory properties of these T-cell subsets independently of each other, recent reports have provided evidence for cross-talk between Tregs and NKT cells, and, consequently, the immunoregulatory networks are seen in a new perspective. Activated NKT cells seem to modulate quantitatively and qualitatively Treg function through IL-2-dependent mechanisms, whereas Tregs can suppress the proliferation, cytokine release and cytotoxic activity of NKT cells by cell-contact-dependent mechanisms. Importantly, Tregs and NKT cells share crucial signaling pathways that could be responsible for their concerted responses. The advances in our understanding of the interactions between distinct subsets of regulatory T cells in autoimmunity might unveil new methods for harnessing these cells with immunotherapeutic properties.

The autoimmune regulator (Aire) controls iNKT cell development and maturation

The mechanism underlying the autoimmune polyglandular syndrome type-1 (APS1) has been attributed to defective T-cell negative selection resulting from reduced expression and presentation of autoantigens in thymic medullary epithelial cells (MECs). It has also been postulated that Aire is involved in development of regulatory T cells, although supporting evidence is lacking. Here we show that expression of Aire in MECs is required for development of iNKT cells, suggesting a role for iNKT cells in APS1.