Yafei Huang

Mouse γδ T cells are capable of expressing MHC class II molecules, and of functioning as antigen-presenting cells

Although human and bovine gammadelta T cells were shown to express MHC class II antigen and function as APCs, attempts to determine if mouse gammabeta T cells have similar functions remained unsuccessful. We now show that gammadelta T cells derived from immunized mice also can be induced to express MHC class II and co-stimulatory molecules after activation in vitro, and are capable of antigen presentation. Using highly purified gammadelta T cells, we found that, unlike human gammadelta T cells, the expression of MHC class II molecules by mouse gammadelta T cells is limited to newly activated cells. Highest levels of MHC class II expression were seen on activated gammadelta T cells that had lost most surface-expressed gammadelta TCR while exhibiting increased levels of intracellular gammadelta TCR. In the absence of further stimulation, MHC class II expression gradually declined with the gammadelta T cells regaining their surface TCR. We also show that cytokine-activated gammadelta T cells can also express MHC class II antigen and exercise antigen-presenting activity.

The Influence of IgE-enhancing and IgE-suppressive γδ T Cells Changes With Exposure to Inhaled Ovalbumin

It has been reported that the IgE response to allergens is influenced by γδ T cells. Intrigued by a study showing that airway challenge of mice with OVA induces in the spleen the development of γδ T cells that suppress the primary IgE response to i.p.-injected OVA-alum, we investigated the γδ T cells involved. We found that the induced IgE suppressors are contained within the Vγ4+ subset of γδ T cells of the spleen, that they express Vδ5 and CD8, and that they depend on IFN-γ for their function. However, we also found that normal nonchallenged mice harbor IgE-enhancing γδ T cells, which are contained within the larger Vγ1+ subset of the spleen. In cell transfer experiments, airway challenge of the donors was required to induce the IgE suppressors among the Vγ4+ cells. Moreover, this challenge simultaneously turned off the IgE enhancers among the Vγ1+ cells. Thus, airway allergen challenge differentially affects two distinct subsets of γδ T cells with nonoverlapping functional potentials, and the outcome is IgE suppression.

A canonical Vγ4Vδ4+ γδ T cell population with distinct stimulation requirements which promotes the Th17 response.

We previously reported a subset of γδ T cells in mice which preferentially responds following intradermal immunization with collagen in complete Freund’s adjuvant (CFA). These cells express a nearly invariant “canonical” Vγ4Vδ4+ TCR. They are potent producers of IL-17A and promote the development of collagen-induced arthritis. In this study, we report that CFA emulsified with PBS alone (without collagen) is sufficient to induce a strong response of Vγ4Vδ4+ cells in the draining lymph nodes of DBA/1 and C57BL/6 mice and that the TCRs of the elicited Vγ4Vδ4+ cells in both strains heavily favor the canonical sequence. However, although both CFA and incomplete Freund’s adjuvant (which lacks the killed mycobacteria present in CFA) induced Vγ4Vδ4+ γδ T cell to expand, only CFA stimulated them to express IL-17A. The route of immunization was also critical, since intraperitoneal CFA induced only a weak response by these cells, whereas intradermal or subcutaneous CFA strongly stimulated them, suggesting that the canonical CFA-elicited Vγ4Vδ4+ cells are recruited from Vγ4+ γδ T cells normally found in the dermis. Their IL-17A response requires the toll-like receptor adapter protein MyD88, and their activation is enhanced by IFNγ, although αβ T cells need not be present. The CFA-elicited Vγ4Vδ4+ γδ T cells show a cytokine profile different from that of other previously described IL-17-producing γδ T cells. Finally, the Vγ4Vδ4+ subset appears to promote the Th17 αβ T cell response, suggesting its importance in mounting an effective immune response against certain pathogens.

Characteristics of IL-17-Producing γδ T Cells

In the August 2009 issue of Immunity (volume 31, number 2), we read with great interest two articles that were written by Martin et al. (2009) and Sutton et al. (2009) and that focused on interleukin-17 (IL-17)-producing γδ T cells. We were, however, surprised to find that both of these papers claim priority for showing that γδ T cells can produce IL-17 without deliberate stimulation via the T cell receptor (TCR). We feel that this claim is unwarranted because in fact at least two previously published papers also arrived at this conclusion (but were not quoted by the authors of either of these Immunity papers).

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.

Peptide antigens for gamma/delta T cells

Abstractγδ T cells express adaptive antigen receptors encoded by rearranging genes. Their diversity is highest in the small region of TCR V–J junctions, especially in the δ chain, which should enable the γδ TCRs to distinguish differences in small epitopes. Indeed, recognition of small molecules, and of an epitope on a larger protein has been reported. Responses to small non-peptides known as phospho-antigens are multi-clonal yet limited to a single γδ T cell subset in humans and non-human primates. Responses to small peptides are multi-clonal or oligo-clonal, include more than one subset of γδ T cells, and occur in rodents and primates. However, less effort has been devoted to investigate the peptide responses. To settle the questions of whether peptides can be ligands for the γδ TCRs, and whether responses to small peptides might occur normally, peptide binding will have to be demonstrated, and natural peptide ligands identified.

Balanced approach of γδ T cells to type 2 immunity

Substantial evidence has been accumulated to indicate that γδ T cells take part in type 2 immune responses. It is not yet clear, however, in what capacity. Apparently, γδ T cells themselves can not only take the function of follicular T helper (TH) cells in certain responses, but also can support responses that are dependent on classical help provided by αβ T cells. Furthermore, the γδ T cells engage as regulators of TH2 immunity. Here, we consider two mouse models that depend on type 2 immunity, non‐specific airway hyperresponsiveness to methacholine after allergen inhalation challenge and the primary IgE response induced by alum‐aided immunization, and examine the function of γδ T cells. In either case, γδ T cells regulate type 2 immunity through balanced enhancing and inhibitory influences. However, after airway allergen exposure, suppressive γδ T cells become dominant. The underlying mechanisms are discussed.

γδ T cells affect IL-4 production and B-cell tolerance

Significance This study changes our understanding of the relationship between T cells and B cells. Although it is known that T cells provide help for specific B-cell responses, it is unclear if and to what extent T cells also influence preimmune B-cell functions. We show here that γδ T cells modulate systemic antibody levels in nonimmunized mice, including all major subclasses and especially IgE antibodies. One mouse strain deficient in certain γδ T cells developed various autoantibodies, whereas mice deficient in all γδ T cells had relatively normal antibodies. Based on these and other findings, we conclude that γδ T cells, influenced by their own cross-talk, affect IL-4 production, B-cell activation, and B-cell tolerance. γδ T cells can influence specific antibody responses. Here, we report that mice deficient in individual γδ T-cell subsets have altered levels of serum antibodies, including all major subclasses, sometimes regardless of the presence of αβ T cells. One strain with a partial γδ deficiency that increases IgE antibodies also displayed increases in IL-4–producing T cells (both residual γδ T cells and αβ T cells) and in systemic IL-4 levels. Its B cells expressed IL-4–regulated inhibitory receptors (CD5, CD22, and CD32) at diminished levels, whereas IL-4–inducible IL-4 receptor α and MHCII were increased. They also showed signs of activation and spontaneously formed germinal centers. These mice displayed IgE-dependent features found in hyper-IgE syndrome and developed antichromatin, antinuclear, and anticytoplasmic autoantibodies. In contrast, mice deficient in all γδ T cells had nearly unchanged Ig levels and did not develop autoantibodies. Removing IL-4 abrogated the increases in IgE, antichromatin antibodies, and autoantibodies in the partially γδ-deficient mice. Our data suggest that γδ T cells, controlled by their own cross-talk, affect IL-4 production, B-cell activation, and B-cell tolerance.

γδ T Cells Shape Preimmune Peripheral B Cell Populations

We previously reported that selective ablation of certain γδ T cell subsets, rather than removal of all γδ T cells, strongly affects serum Ab levels in nonimmunized mice. This type of manipulation also changed T cells, including residual γδ T cells, revealing some interdependence of γδ T cell populations. For example, in mice lacking Vγ4+ and Vγ6+ γδ T cells (B6.TCR-Vγ4−/−/6−/−), we observed expanded Vγ1+ cells, which changed in composition and activation and produced more IL-4 upon stimulation in vitro, increased IL-4 production by αβ T cells as well as spontaneous germinal center formation in the spleen, and elevated serum Ig and autoantibodies. We therefore examined B cell populations in this and other γδ-deficient mouse strains. Whereas immature bone marrow B cells remained largely unchanged, peripheral B cells underwent several changes. Specifically, transitional and mature B cells in the spleen of B6.TCR-Vγ4−/−/6−/− mice and other peripheral B cell populations were diminished, most of all splenic marginal zone (MZ) B cells. However, relative frequencies and absolute numbers of Ab-producing cells, as well as serum levels of Abs, IL-4, and BAFF, were increased. Cell transfers confirmed that these changes are directly dependent on the altered γδ T cells in this strain and on their enhanced potential of producing IL-4. Further evidence suggests the possibility of direct interactions between γδ T cells and B cells in the splenic MZ. Taken together, these data demonstrate the capability of γδ T cells of modulating size and productivity of preimmune peripheral B cell populations.

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.