Jason S. Ellis

Innocuous IFNγ induced by adjuvant-free antigen restores normoglycemia in NOD mice through inhibition of IL-17 production

The role of Th17 cells in type I diabetes (TID) remains largely unknown. Glutamic acid decarboxylase (GAD) sequence 206–220 (designated GAD2) represents a late-stage epitope, but GAD2-specific T cell receptor transgenic T cells producing interferon γ (IFNγ) protect against passive TID. Because IFNγ is known to inhibit Th17 cells, effective presentation of GAD2 peptide under noninflammatory conditions may protect against TID at advanced disease stages. To test this premise, GAD2 was genetically incorporated into an immunoglobulin (Ig) molecule to magnify tolerance, and the resulting Ig-GAD2 was tested against TID at different stages of the disease. The findings indicated that Ig-GAD2 could not prevent TID at the preinsulitis phase, but delayed TID at the insulitis stage. More importantly, Ig-GAD2 sustained both clearance of pancreatic cell infiltration and β-cell division and restored normoglycemia when given to hyperglycemic mice at the prediabetic stage. This was dependent on the induction of splenic IFNγ that inhibited interleukin (IL)-17 production. In fact, neutralization of IFNγ led to a significant increase in the frequency of Th17 cells, and the treatment became nonprotective. Thus, IFNγ induced by an adjuvant free antigen, contrary to its usual inflammatory function, restores normoglycemia, most likely by localized bystander suppression of pathogenic IL-17–producing cells.

Specific T Regulatory Cells Display Broad Suppressive Functions against Experimental Allergic Encephalomyelitis upon Activation with Cognate Antigen

To date, very few Ag-based regimens have been defined that could expand T regulatory (Treg) cells to reverse autoimmunity. Additional understanding of Treg function with respect to specificity and broad suppression should help overcome these limitations. Ig-proteolipid protein (PLP)1, an Ig carrying a PLP1 peptide corresponding to amino acid residues 139-151 of PLP, displayed potent tolerogenic functions and proved effective against experimental allergic encephalomyelitis (EAE). In this study, we took advantage of the Ig-PLP1 system and the PLP1-specific TCR transgenic 5B6 mouse to define a regimen that could expand Ag-specific Treg cells in vivo and tested for effectiveness against autoimmunity involving diverse T cell specificities. The findings indicate that in vivo exposure to aggregated Ig-PLP1 drives PLP1-specific 5B6 TCR transgenic cells to evolve as Treg cells expressing CD25, CTLA-4, and Foxp3 and producing IL-10. These Treg cells were able to suppress PLP1 peptide-induced EAE in both SJL/J and F1 (SJL/J × C57BL/6) mice. However, despite being effective against disease induced with a CNS homogenate, the Treg cells were unable to counter EAE induced by a myelin basic protein or a myelin oligodendrocyte glycoprotein peptide. Nevertheless, activation with Ag before transfer into the host mice supports suppression of both myelin oligodendrocyte glycoprotein- and myelin basic protein peptide-induced EAE. Thus, it is suggested that activation of Treg cells by the cognate autoantigen is necessary for operation of broad suppressive functions.

Delayed maturation of an IL-12–producing dendritic cell subset explains the early Th2 bias in neonatal immunity

Primary neonatal T cell responses comprise both T helper (Th) cell subsets, but Th1 cells express high levels of interleukin 13 receptor α1 (IL-13Rα1), which heterodimerizes with IL-4Rα. During secondary antigen challenge, Th2-produced IL-4 triggers the apoptosis of Th1 cells via IL-4Rα/IL-13Rα1, thus explaining the Th2 bias in neonates. We show that neonates acquire the ability to overcome the Th2 bias and generate Th1 responses starting 6 d after birth. This transition was caused by the developmental maturation of CD8α+CD4− dendritic cells (DCs), which were minimal in number during the first few days of birth and produced low levels of IL-12. This lack of IL-12 sustained the expression of IL-13Rα1 on Th1 cells. By day 6 after birth, however, a significant number of CD8α+CD4− DCs accumulated in the spleen and produced IL-12, which triggered the down-regulation of IL-13Rα1 expression on Th1 cells, thus protecting them against IL-4–driven apoptosis.

FoxP3+RORγt+ T Helper Intermediates Display Suppressive Function against Autoimmune Diabetes

Recently, traces of double-positive FoxP3+RORγt+ T cells were identified and viewed as dual programming differentiation intermediates geared toward development into T regulatory or Th17 cells. In this study, we report that FoxP3+RORγt+ intermediates arise in the NOD mouse T cell repertoire prior to inflammation and can be expanded with tolerogen without further differentiation. Furthermore, FoxP3+RORγt+ cells express both CD62L and membrane-bound TGFβ and use the former to traffic to the pancreas and the latter to suppress effector T cells both in vitro and in vivo. The cells perform these functions as FoxP3+RORγt+ intermediates, despite being able to terminally differentiate into either FoxP3+RORγt− T regulatory or FoxP3−RORγt+ Th17 cells on polarization. These previously unrecognized observations extend plasticity to both differentiation and function and indicate that the intermediates are poised to traffic to sites of inflammation and target diverse pathogenic T cells, likely without prior conditioning by effector T cells, thus broadening efficacy against autoimmunity.

Comparison of sensitivity of Th1, Th2, and Th17 cells to Fas-mediated apoptosis

Following activation through the TCR, CD4+ T cells can differentiate into three major subsets: Th1, Th2, and Th17 cells. IL‐17‐secreting Th17 cells play an important role in the pathogenesis of several autoimmune diseases and in immune responses to pathogens, but little is known about the regulation of apoptosis in Th17 cells. In this study, the sensitivity of in vitro‐polarized Th1, Th2, and Th17 cells to Fas‐mediated apoptosis was compared directly by different methods. The order of sensitivity of T cell subsets to Fas‐mediated apoptosis is: Th1 > Th17 > Th2. The greater sensitivity of Th17 cells to Fas‐mediated apoptosis compared with Th2 cells correlated with their higher expression of FasL and comparable expression of the antiapoptotic molecule FLIP. The decreased sensitivity of Th17 compared with Th1 cells correlated with the higher expression of FLIP by Th17 cells. Transgenic overexpression of FLIP in T cells protected all three subsets from Fas‐mediated apoptosis. These findings provide new knowledge for understanding how survival of different subsets of T cells is regulated.

Transient depletion of CD4+ CD25+ regulatory T cells results in multiple autoimmune diseases in wild‐type and B‐cell‐deficient NOD mice

Approximately 80% of female wild‐type non‐obese diabetic (WT NOD) mice spontaneously develop diabetes, whereas B‐cell‐deficient (B−/−) NOD mice are resistant to diabetes. B−/− mice are also resistant to other spontaneous and experimentally induced autoimmune diseases, including arthritis, systemic lupus erythematosus, Sjögren syndrome and thyroiditis. Under normal conditions, activation of self‐reactive T cells in the periphery is limited by CD4+ CD25+ natural regulatory T (Treg) cells. B−/− NOD.H‐2h4 mice, normally resistant to spontaneous autoimmune thyroiditis (SAT), develop SAT when Treg cells are depleted, suggesting that Treg cells are preferentially activated when autoantigen is initially presented by non‐B‐cell antigen‐presenting cells. To test the hypothesis that increased Treg cell activity in B−/− mice contributes to their resistance to other autoimmune diseases, WT and B−/− NOD mice were given anti‐CD25 to transiently deplete CD4+ CD25+ Treg cells. The WT and B−/− NOD mice given anti‐CD25 developed diabetes much earlier than WT mice given rat IgG, whereas rat IgG‐treated B−/− mice did not develop diabetes. Treg‐cell‐depleted mice had increased lymphocyte infiltration of the pancreas, salivary glands and thyroid compared with controls given rat IgG. These results are consistent with the hypothesis that resistance of B‐cell‐deficient NOD mice to several autoimmune diseases is due to the activity of Treg cells.

Fetal Exposure to High-Avidity TCR Ligand Enhances Expansion of Peripheral T Regulatory Cells

Lately, it has become clear that regulatory T cells (Tregs) play a major role in the maintenance of peripheral tolerance and control of autoimmunity. Despite these critical functions, the process underlying the development of Tregs remains largely undefined. Herein, altered peptide ligand (APL) variants derived from the proteolipid protein-1 (PLP1) epitope were expressed on immunoglobulins (Igs) and the resulting Ig-APLs were used to deliver the APLs from mother to fetus through the maternal placenta to influence thymic T cell selection. This delivery system was then adapted to the SJL/J mouse, a strain that expresses only the DM20 form of PLP, which lacks the dominant PLP1 epitope in the thymus during fetal and neonatal development. This model, which restores thymic T cell selection for PLP1, was then used to determine whether affinity plays a role in the development of Tregs. The findings show that fetal exposure to low-affinity peptide ligand was unable to drive development of Tregs while variants with higher affinity to the TCR resulted in significant seeding of the periphery with mature, naive Tregs. Thus, contrary to pathogenic T cells, Tregs require avid TCR-ligand interaction to undergo thymic development and maturation.

Transient depletion of B cells in young mice results in activation of regulatory T cells that inhibit development of autoimmune disease in adults

B-cell depletion therapy can be effective for treating B-cell lymphomas as well as many human and murine autoimmune diseases. B-cell-deficient mice are normally resistant to spontaneous autoimmune thyroiditis (SAT), but they develop SAT if regulatory T cells are transiently depleted during the first 3-6 weeks after birth. This was also a critical time when B-cell depletion effectively inhibited development of SAT in adult mice. The current study was undertaken to test the hypothesis that transient depletion of B cells using anti-CD20 would be sufficient to suppress SAT if B cells were depleted early in life and that inhibition of SAT would be due to the activity of Treg that functioned most effectively when B cells were absent or low. The results presented here support this hypothesis and indicate that development of autoimmune disease in adults is effectively inhibited when anti-CD20 is administered 1-3 weeks after birth. After 3 weeks, transient B-cell depletion is no longer effective, and B-cell depletion must be maintained to effectively suppress autoimmune disease. B-cell depletion in 1- to 3-week-old mice depletes all B-cell subsets, whereas B-cell depletion initiated in adults spares many marginal zone B cells. Following early B-cell depletion, splenic Treg increase in number, and depletion of Treg reverses the inhibitory effect of anti-CD20 on disease development. Early transient depletion of B cells could be useful for preventing autoimmune disease in individuals at high risk for developing autoimmune diseases as adults.

Reduced Effectiveness of CD4+Foxp3+ Regulatory T Cells in CD28-Deficient NOD.H-2h4 Mice Leads to Increased Severity of Spontaneous Autoimmune Thyroiditis

NOD.H-2h4 mice given NaI in their drinking water develop iodine-accelerated spontaneous autoimmune thyroiditis (ISAT) with chronic inflammation of the thyroid by T and B cells and production of anti-mouse thyroglobulin (MTg) autoantibody. CD28−/− NOD.H-2h4 mice, which have reduced numbers of CD4+Foxp3+ regulatory T cells (Tregs), were developed to examine the role of Tregs in ISAT development. CD28−/− NOD.H2-h4 mice develop more severe ISAT than do wild-type (WT) mice, with collagen deposition (fibrosis) and low serum T4. CD28−/− mice have increased expression of proinflammatory cytokines IFN-γ and IL-6, consistent with increased mononuclear cell infiltration and tissue destruction in thyroids. Importantly, transferring purified CD4+Foxp3+ Tregs from WT mice reduces ISAT severity in CD28−/− mice without increasing the total number of Tregs, suggesting that endogenous Tregs in CD28−/− mice are functionally ineffective. Endogenous CD28−/− Tregs have reduced surface expression of CD27, TNFR2 p75, and glucocorticoid-induced TNFR-related protein compared with transferred CD28+/+ Tregs. Although anti-MTg autoantibody levels generally correlate with ISAT severity scores in WT mice, CD28−/− mice have lower anti-MTg autoantibody responses than do WT mice. The percentages of follicular B cells are decreased and those of marginal zone B cells are increased in spleens of CD28−/− mice, and they have fewer thyroid-infiltrating B cells than do WT mice. This suggests that CD28 deficiency has direct and indirect effects on the B cell compartment. B cell–deficient (B−/−) NOD.H-2h4 mice are resistant to ISAT, but CD28−/−B−/− mice develop ISAT comparable to WT mice and have reduced numbers of Tregs compared with WT B−/− mice.

T Cell Dynamics during Induction of Tolerance and Suppression of Experimental Allergic Encephalomyelitis

The cell dynamics associated with induction of peripheral T cell tolerance remain largely undefined. In this study, an in vivo model was adapted to two-photon microscopy imaging, and T cell behavior was analyzed on tolerogen-induced modulation. FcγR-deficient (FcγR−/−) mice were unable to resist or alleviate experimental allergic encephalomyelitis when treated with Ig-myelin oligodendrocyte glycoprotein (MOG) tolerogen, an Ig carrying the MOG35–55 peptide. However, when FcγR+/+ dendritic cells (DCs) are adoptively transferred into FcγR−/− mice, uptake and presentation of Ig-MOG occurs and the animals were able to overcome experimental allergic encephalomyelitis. We then fluorescently labeled FcγR+/+ DCs and 2D2 MOG-specific TCR-transgenic T cells, transferred them into FcγR−/− mice, administered Ig-MOG, and analyzed both T cell–DC contact events and T cell motility. The results indicate that tolerance takes place in lymphoid organs, and surprisingly, the T cells do not become anergic but instead have a Th2 phenotype. The tolerant Th2 cells displayed reduced motility after tolerogen exposure similar to Th1 cells after immunization. However, the Th2 cells had higher migration speeds and took longer to exhibit changes in motility. Therefore, both Th1 immunity and Th2 tolerance alter T cell migration on Ag recognition, but the kinetics of this effect differ among the subsets.