Rebecca L. O'Brien

IL-17-Producing γδ T Cells

IL‐17 is produced not only by CD4+ αβ T cells, but also CD8+ αβ T cells, NKT cells, and γδ T cells, plus some non‐T cells, including macrophages and neutrophils. The ability of IL‐17 to deploy neutrophils to sites of inflammation imparts this cytokine with a key role in diseases of several types. Surprisingly, γδ T cells are responsible for much of the IL‐17 produced in several disease models, particularly early on.

IL-17-producing gammadelta T cells.

IL‐17 is produced not only by CD4+ αβ T cells, but also CD8+ αβ T cells, NKT cells, and γδ T cells, plus some non‐T cells, including macrophages and neutrophils. The ability of IL‐17 to deploy neutrophils to sites of inflammation imparts this cytokine with a key role in diseases of several types. Surprisingly, γδ T cells are responsible for much of the IL‐17 produced in several disease models, particularly early on.

Airway hyperresponsiveness through synergy of γδ T cells and NKT cells

Mice sensitized and challenged with OVA were used to investigate the role of innate T cells in the development of allergic airway hyperresponsiveness (AHR). AHR, but not eosinophilic airway inflammation, was induced in T cell-deficient mice by small numbers of cotransferred γδ T cells and invariant NKT cells, whereas either cell type alone was not effective. Only Vγ1+Vδ5+ γδ T cells enhanced AHR. Surprisingly, OVA-specific αβ T cells were not required, revealing a pathway of AHR development mediated entirely by innate T cells. The data suggest that lymphocytic synergism, which is key to the Ag-specific adaptive immune response, is also intrinsic to T cell-dependent innate responses.

Gamma Delta T Cell Receptors Confer Autonomous Responsiveness To The Insulin Peptide B:9–23

The range and physical qualities of molecules that act as ligands for the gammadelta T cell receptors (TCRs) remain uncertain. Processed insulin is recognized by alphabeta T cells, which mediate diabetes in non-obese diabetic (NOD) mice. Here, we present evidence that gammadelta T cells in these mice recognize processed insulin as well. Hybridomas generated from NOD spleen and pancreatic lymph nodes included clones expressing gammadelta TCRs that responded specifically to purified islets of Langerhans and to an insulin peptide, but not to intact insulin. The gammadelta TCRs associated with this type of response are diverse, but a cloned gammadelta TCR was sufficient to transfer the response. The response to the insulin peptide was autonomous as demonstrated by stimulating single responder cells in isolation. This study reveals a novel specificity for gammadelta TCRs, and raises the possibility that gammadelta T cells become involved in islet-specific autoimmunity.

Allergic Airway Hyperresponsiveness-Enhancing γδ T Cells Develop in Normal Untreated Mice and Fail to Produce IL-4/13, Unlike Th2 and NKT Cells

Allergic airway hyperresponsiveness (AHR) in OVA-sensitized and challenged mice, mediated by allergen-specific Th2 cells and Th2-like invariant NKT (iNKT) cells, develops under the influence of enhancing and inhibitory γδ T cells. The AHR-enhancing cells belong to the Vγ1+ γδ T cell subset, cells that are capable of increasing IL-5 and IL-13 levels in the airways in a manner like Th2 cells. They also synergize with iNKT cells in mediating AHR. However, unlike Th2 cells, the AHR enhancers arise in untreated mice, and we show here that they exhibit their functional bias already as thymocytes, at an HSAhigh maturational stage. In further contrast to Th2 cells and also unlike iNKT cells, they could not be stimulated to produce IL-4 and IL-13, consistent with their synergistic dependence on iNKT cells in mediating AHR. Mice deficient in IFN-γ, TNFRp75, or IL-4 did not produce these AHR-enhancing γδ T cells, but in the absence of IFN-γ, spontaneous development of these cells was restored by adoptive transfer of IFN-γ-competent dendritic cells from untreated donors. The i.p. injection of OVA/aluminum hydroxide restored development of the AHR enhancers in all of the mutant strains, indicating that the enhancers still can be induced when they fail to develop spontaneously, and that they themselves need not express TNFRp75, IFN-γ, or IL-4 to exert their function. We conclude that both the development and the cytokine potential of the AHR-enhancing γδ T cells differs critically from that of Th2 cells and NKT cells, despite similar influences of these cell populations on AHR.

CD4 T cells play important roles in maintaining IL-17-producing γδ T-cell subsets in naive animals.

A proportional balance between αβ and γδ T‐cell subsets in the periphery is exceedingly well maintained by a homeostatic mechanism. However, a cellular mechanism underlying the regulation remains undefined. We recently reported that a subset of developing γδ T cells spontaneously acquires interleukin (IL)‐17‐producing capacity even within naive animals through a transforming growth factor (TGF)β1‐dependent mechanism, thus considered ‘innate’ IL‐17‐producing cells. Here, we report that γδ T cells generated within αβ T cell (or CD4 T cell)‐deficient environments displayed altered cytokine profiles; particularly, ‘innate’ IL‐17 expression was significantly impaired compared with those in wild‐type mice. Impaired IL‐17 production in γδ T cells was directly related to CD4 T‐cell deficiency, because depletion of CD4 T cells in wild‐type mice diminished and adoptive CD4 T‐cell transfer into T‐cell receptor β−/− mice restored IL‐17 expression in γδ T cells. CD4 T cell‐mediated IL‐17 expression required TGFβ1. Moreover, Th17 but not Th1 or Th2 effector CD4 T cells were highly efficient in enhancing γδ T‐cell IL‐17 expression. Taken together, our results highlight a novel CD4 T cell‐dependent mechanism that shapes the generation of IL‐17+ γδ T cells in naive settings.

Antigen-Specific Regulation of IgE Antibodies by Non-Antigen–Specific γδ T Cells

We re-examined the observation that γδ T cells, when transferred from mice tolerized to an inhaled conventional Ag, suppress the allergic IgE response to this Ag specifically. Using OVA and hen egg lysozyme in crisscross fashion, we confirmed the Ag-specific IgE-regulatory effect of the γδ T cells. Although only Vγ4+ γδ T cells are regulators, the Ag specificity does not stem from specificity of their γδ TCRs. Instead, the Vγ4+ γδ T cells failed to respond to either Ag, but rapidly acquired Ag-specific regulatory function in vivo following i.v. injection of non-T cells derived from the spleen of Ag-tolerized mice. This correlated with their in vivo Ag acquisition from i.v. injected Ag-loaded splenic non-T cells, and in vivo transfer of membrane label provided evidence for direct contact between the injected splenic non-T cells and the Vγ4+ γδ T cells. Together, our data suggest that Ag itself, when acquired by γδ T cells, directs the specificity of their IgE suppression.

Protective role of γδ T cells in spontaneous ocular inflammation.

PURPOSEnA role for gammadelta T cells in immunoregulation has been shown in a number of studies, but in the absence of infection or induced disease, mice lacking gammadelta T cells generally appear to be healthy. That certain mice lacking gammadelta T cells often spontaneously develop keratitis, characterized by a progressive and destructive inflammation of the cornea is reported here.nnnMETHODSnThe keratitis developing in these mice was characterized in terms of prevalence in males versus females, age of onset, and histologic features. Attempts were made to understand the underlying causes of the disease by removing alphabeta T cells, altering sex hormones, and reconstituting gammadelta T cells.nnnRESULTSnThe development of keratitis in these mice depended on the C57BL/10 genetic background, and was much more common among females than males. The incidence of the disease increased with age, exceeding 80% in females greater than 18 weeks old. Evidence that the keratitis in these mice is at least partly autoimmune in nature, and that despite its prevalence in females, male hormones do not protect against the disease is presented.nnnCONCLUSIONSnThese findings indicate an important role for gammadelta T cells in maintaining immune balance in the eye. The mice described in this study represent a potential new small animal model of keratitis.

γδ T Cell–Dependent Regulatory T Cells Prevent the Development of Autoimmune Keratitis

To prevent potentially damaging inflammatory responses, the eye actively promotes local immune tolerance via a variety of mechanisms. Owing to trauma, infection, or other ongoing autoimmunity, these mechanisms sometimes fail, and an autoimmune disorder may develop in the eye. In mice of the C57BL/10 (B10) background, autoimmune keratitis often develops spontaneously, particularly in the females. Its incidence is greatly elevated in the absence of γδ T cells, such that ∼80% of female B10.TCRδ−/− mice develop keratitis by 18 wk of age. In this article, we show that CD8+ αβ T cells are the drivers of this disease, because adoptive transfer of CD8+, but not CD4+, T cells to keratitis-resistant B10.TCRβ/δ−/− hosts induced a high incidence of keratitis. This finding was unexpected because in other autoimmune diseases, more often CD4+ αβ T cells, or both CD4+ and CD8+ αβ T cells, mediate the disease. Compared with wild-type B10 mice, B10.TCRδ−/− mice also show increased percentages of peripheral memory phenotype CD8+ αβ T cells, along with an elevated frequency of CD8+ αβ T cells biased to produce inflammatory cytokines. In addition, B10.TCRδ−/- mice have fewer peripheral CD4+ CD25+ Foxp3+ αβ regulatory T cells (Tregs), which express lower levels of receptors needed for Treg development and function. Together, these observations suggest that in B10 background mice, γδ T cells are required to generate adequate numbers of CD4+ CD25+ Foxp3+ Tregs, and that in B10.TCRδ−/− mice a Treg deficiency allows dysregulated effector or memory CD8+ αβ T cells to infiltrate the cornea and provoke an autoimmune attack.

αβ TCR⁺ T cells, but not B cells, promote autoimmune keratitis in b10 mice lacking γδ T cells.

PURPOSEnTo investigate additional factors in the spontaneous development of keratitis previously reported in B10.TCRδ⁻/⁻ female mice.nnnMETHODSnThe study tested whether susceptible B10.TCRδ⁻/⁻ mice have dry eyes compared with resistant B6.TCRδ⁻/⁻ females and also rederived the B10.TCRδ⁻/⁻ strain to test for the role of an infectious agent. Also assessed was whether adoptive transfer of αβ T cells from autoimmune mice induced keratitis in resistant mice. In addition, a potential role was examined for B cells or autoantibodies by B-cell inactivation, and the role of female hormones was tested by ovariectomy. Finally, the study investigated whether adoptive transfer of Vγ1⁺ γδ T cells confers protection.nnnRESULTSnTear production in B10.TCRδ⁻/⁻ females was actually higher than in B6.TCRδ⁻/⁻ controls. Rederived B10.TCRδ⁻/⁻ mice still developed keratitis. Keratitis was induced in resistant mice after adoptive transfer of αβ T cells from keratitic donors. Inactivation of B cells from susceptible mice had no effect on the development of keratitis. Ovariectomy did not significantly reduce disease in B10.TCRδ⁻/⁻ females. Adoptive transfer of Vγ1⁺ cells from wild-type donors reduced keratitis in B10.TCRδ⁻/⁻ females.nnnCONCLUSIONSnNeither low tear levels nor ovarian hormones contribute to spontaneous keratitis in B10.TCRδ⁻/⁻ female mice, nor does it appear to depend on an infectious agent carried vertically in this strain. However, αβ T cells from keratitic hosts are sufficient to induce disease in the resistant B10.TCRβ⁻/⁻δ⁻/⁻ strain. Autoaggressive αβ T cells in the absence of Vγ1⁺ T cells in B10.TCRδ⁻/⁻ mice may be insufficiently checked to prevent disease.