Preferentially expanding Vγ1+ γδ T cells are associated with protective immunity against Plasmodium infection in mice

γδ T cells play a crucial role in controlling malaria parasites. Dendritic cell (DC) activation via CD40 ligand (CD40L)‐CD40 signaling by γδ T cells induces protective immunity against the blood‐stage Plasmodium berghei XAT (PbXAT) parasites in mice. However, it is unknown which γδ T‐cell subset has an effector role and is required to control the Plasmodium infection. Here, using antibodies to deplete TCR Vγ1⁺ cells, we saw that Vγ1⁺ γδ T cells were important for the control of PbXAT infection. Splenic Vγ1⁺ γδ T cells preferentially expand and express CD40L, and both Vγ1⁺ and Vγ4⁺ γδ T cells produce IFN‐γ during infection. Although expression of CD40L on Vγ1⁺ γδ T cells is maintained during infection, the IFN‐γ positivity of Vγ1⁺ γδ T cells is reduced in late‐phase infection due to γδ T‐cell dysfunction. In Plasmodium‐infected IFN‐γ signaling‐deficient mice, DC activation is reduced, resulting in the suppression of γδ T‐cell dysfunction and the dampening of γδ T‐cell expansion in the late phase of infection. Our data suggest that Vγ1⁺ γδ T cells represent a major subset responding to PbXAT infection and that the Vγ1⁺ γδ T‐cell response is dependent on IFN‐γ‐activated DCs.     

Cytomegalovirus drives Vδ2neg γδ T cell inflation in many healthy virus carriers with increasing age

Cytomegalovirus (CMV) usually causes lifelong asymptomatic infection, but over time can distort immune profiles. Recent reports describe selective expansion of Vδ2^neg γδ T cells in healthy and immunocompromised CMV carriers. Having shown previously that virus‐specific CD8⁺ and CD4⁺ T cell responses are increased significantly in elderly CMV carriers, probably driven by chronic stimulation, we hypothesized that Vδ2^neg γδ T cells may also be expanded with age. Our results show that Vδ2^neg γδ T cells are increased significantly in CMV‐seropositive healthy individuals compared to CMV‐seronegative controls in all age groups. The differences were most significant in older age groups (P < 0·0001). Furthermore, while Vδ2^neg γδ T‐ cells comprise both naive and memory cells in CMV‐seronegative donors, highly differentiated effector memory cells are the dominant phenotype in CMV carriers, with naive cells reduced significantly in numbers in CMV‐seropositive elderly. Although phenotypically resembling conventional CMV‐specific T cells, Vδ2^neg γδ T cells do not correlate with changes in magnitude of CMV‐specific CD4⁺ or CD8⁺ T cell frequencies within those individuals, and do not possess ex‐vivo immediate effector function as shown by CMV‐specific CD4⁺ and CD8⁺ T cells. However, after short‐term culture, Vδ2^neg γδ T cells demonstrate effector T cell functions, suggesting additional requirements for activation. In summary, Vδ2^neg γδ T cells are expanded in many older CMV carriers, demonstrating a further level of lymphocyte subset skewing by CMV in healthy individuals. As others have reported shared reactivity of Vδ2^neg γδ T cells towards tumour cells, the composition of γδ T cell subsets may also have implications for risk of developing cancer in elderly people.     

A regulatory cross‐talk between Vγ9Vδ2 T lymphocytes and mesenchymal stem cells

The physiological functions of human TCRVγ9Vδ2⁺ γδ lymphocytes reactive to non‐peptide phosphoantigens contribute to cancer immunosurveillance and immunotherapy. However, their regulation by mesenchymal stem cells (MSC), multipotent and immunomodulatory progenitor cells able to infiltrate tumors, has not been investigated so far. By analyzing freshly isolated TCRVγ9Vδ2⁺ lymphocytes and primary cell lines stimulated with synthetic phosphoantigen or B‐cell lymphoma cell lines in the presence of MSC, we demonstrated that MSC were potent suppressors of γδ‐cell proliferation, cytokine production and cytolytic responses in vitro. This inhibition was mediated by the COX‐2‐dependent production of prostaglandin E2 (PGE₂) and by MSC through EP2 and EP4 inhibitory receptors expressed by Vγ9Vδ2 T lymphocytes. COX‐2 expression and PGE₂ production by MSC were not constitutive, but were induced by IFN‐γ and TNF‐α secreted by activated Vγ9Vδ2 T cells. This regulatory cross‐talk between MSC and Vγ9Vδ2 T lymphocytes involving PGE₂ could be of importance for the antitumor and antimicrobial activities of γδ T cells.     

CCR6 and NK1.1 distinguish between IL‐17A and IFN‐γ‐producing γδ effector T cells

γδ T cells are a potent source of innate IL‐17A and IFN‐γ, and they acquire the capacity to produce these cytokines within the thymus. However, the precise stages and required signals that guide this differentiation are unclear. Here we show that the CD24^low CD44^high effector γδ T cells of the adult thymus are segregated into two lineages by the mutually exclusive expression of CCR6 and NK1.1. Only CCR6⁺ γδ T cells produced IL‐17A, while NK1.1⁺ γδ T cells were efficient producers of IFN‐γ but not of IL‐17A. Their effector phenotype correlated with loss of CCR9 expression, particularly among the NK1.1⁺ γδ T cells. Accordingly, both γδ T‐cell subsets were rare in gut‐associated lymphoid tissues, but abundant in peripheral lymphoid tissues. There, they provided IL‐17A and IFN‐γ in response to TCR‐specific and TCR‐independent stimuli. IL‐12 and IL‐18 induced IFN‐γ and IL‐23 induced IL‐17A production by NK1.1⁺ or CCR6⁺ γδ T cells, respectively. Importantly, we show that CCR6⁺ γδ T cells are more responsive to TCR stimulation than their NK1.1⁺ counterparts. In conclusion, our findings support the hypothesis that CCR6⁺ IL‐17A‐producing γδ T cells derive from less TCR‐dependent selection events than IFN‐γ‐producing NK1.1⁺ γδ T cells.     

4–1BB signal stimulates the activation,expansion, and effector functions of γδ T cells in mice and humans

We show here that the expression of 4–1BB is rapidly induced in γδ T cells following antigenic stimulation in both mice and humans, and ligation of the newly acquired 4–1BB with an agonistic anti‐4–1BB augments cell division and cytokine production. We further demonstrate that γδ rather than αβ T cells protect mice from Listeria monocytogenes (LM) infection and 4–1BB stimulation enhances the γδ T‐cell activities in the acute phase of LM infection. IFN‐γ produced from γδ T cells was the major soluble factor regulating LM infection. Vγ1⁺ T cells were expanded in LM‐infected mice and 4–1BB signal triggered an exclusive expansion of Vγ1⁺ T cells and induced IFN‐γ in these Vγ1⁺ T cells. Similarly, 4–1BB was induced on human γδ T cells and shown to be fully functional. Combination treatment with human γδ T cells and anti‐hu4–1BB effectively protected against LM infection in human γδ T cell‐transferred NOD‐SCID mice. Taken together, these data provide evidence that the 4–1BB signal is an important regulator of γδ T cells and induces robust host defense against LM infection.     

γδ T cells come to stay: Innate skin memory in the Aldara model

The term immunological memory has long been a trademark restricted to adaptive lymphocytes such as memory B cells and plasma cells as well as memory CD8⁺ αβ T cells. In recent years, innate lymphocytes such as NK cells have also been shown to adapt to their environment by antigen‐specific expansion and selective survival. However, whether γδ T cells mount comparable memory responses to pathogenic stimuli is less well understood. In this issue of European Journal of Immunology, Hartwig et al. [Eur. J. Immunol. 2015. 45: 3022–3033] identify a subset of IL‐17‐producing γδ T cells that are capable of establishing long‐lived memory in the skin of mice exposed to imiquimod in the Aldara psoriasis model. These γδ T cells uniformly express a Vγ4⁺Vδ4⁺ TCR. They produce IL‐17A/F and persist in the dermis for long periods of time, also at untreated distal sites. Upon secondary challenge, experienced Vγ4⁺Vδ4⁺ cells show enhanced effector functions and mediate exacerbated secondary inflammation. These findings showcase innate γδ T‐cell memory that uses a single conserved public TCR combination. Furthermore, they provide mechanistic insight to the observed psoriatic relapses in patients in response to topical treatment with imiquimod.     

γδ cells involved in contact sensitivity preferentially rearrange the Vγ3 region and require interleukin-7

Ptak and Askenase showed that both αβ and γδ cells are required for transfer of contact sensitivity (CS). This study confirms that day 4 immune cells depleted of γδ cells fail to transfer CS to trinitrochlorobenzene (TNP-Cl) systemically and demonstrates that administration of anti-γδ monoclonal antibodies (mAb) in vivo abolishes the CS reaction. Moreover, γδ cells accumulate at the antigen challenge site: these cells have the unusual phenotype CD8α⁺, CD8β^-, IL-4 R⁺ which we suggest is due to their state of activation. Following immunization with contact sensitizer on the skin, the absolute number of γδ cells increases in the regional lymph nodes with a peak at 4 days. Of the γδ cells, 80%, both in the lymph nodes of TNP-Cl-immune mice and accumulating at the antigen challenge site are Vγ3⁺. The γδ cells expressing Vγ3, which is characteristic of dendritic epithelial T cells (DETC), obtained 4 days after sensitization, proliferate in response to interleukin (IL)-7, but only poorly to IL-2 and IL-4. They also respond to concanavalin A and immobilized anti-γδ mAb, but not to haptens or heat-shocked syngeneic spleen cells. Furthermore, injection of mice with mAb to IL-7 inhibits accumulation of Vγ3⁺ cells both in the lymph nodes after skin sensitization and at the antigen-challenge site. Altogether, these results strongly support the view that DETC are related to, or the original source of, the γδ cells found in the lymph node after skin sensitization and at the site of challenge, and that IL-7 is implicated in these phenomena.     

Helper activity of CD4+ αβ T cells is required for the avian γδ T cell response

We have studied the in vitro activation of chicken γδ T cells. Both splenic αβ and γδ T cells obtained from complete Freund's adjuvant-primed chickens proliferated in vitro when stimulated with mycobacterial sonicate or purified protein derivative of Mycobacterium tuberculosis. When CD4⁺ cells or αβ T cell receptor (TcR)-positive cells were removed, both the proliferation and the blast formation of γδ T cells in response to mycobacterial antigens were abrogated. The response was restored if supernatant from concanavalin A (Con A)-activated lymphocyte cultures (CAS) as a source of helper factors was added together with the specific antigen purified protein derivative. The CD4- or αβ TcR-depleted cells still proliferated in response to Con A, although a decrease of the response was observed. To analyze the γδ T cell response more specifically we stimulated peripheral blood cells with immobilized monoclonal antibodies against T cell receptor. Anti-γδ TcR antibody alone did not induce significant proliferation. When CAS was added together with the anti-γδ TcR monoclonal antibody, a strong proliferation of γδ T cells was observed. In contrast, both Vβ1- and Vβ2-expressing αβ T cells proliferated in vitro in response to stimulation with the relevant anti-TcR monoclonal antibody alone. Depletion of either Vβ1⁺ or Vβ2⁺ T cell subset alone had no negative effect on the proliferation or blast formation of γδ T cells stimulated with mycobacterial antigens. Taken together our results suggest that CD4⁺ αβ T cells (both Vβl- and Vβ2-expressing) play a role in the activation and response of chicken γδ T cells.     

Expansion of CD56+ NK T and γδ T cells from cord blood of human neonates

A particular T cell population expressing NK cell markers, CD56 and CD57, exists in humans. Many CD56⁺ T and CD57⁺ T cells (i.e. NK T cells) exist in the liver and increase in number in the blood with ageing. They may be a human counterpart of extrathymic T cells, similar to NK1.1⁺ CD3^int cells seen in mice. We investigate here the existence of such NK T cells in human cord blood and the in vitro expansion of these cells by the stimulation of human recombinant IL-2 (rIL-2). There were very small populations (< 1.0%) of CD56⁺ T cells, CD57⁺ T cells, and γδ T cells in cord blood. However, all of these populations increased in number after birth and with ageing. When lymphocytes in cord blood were cultured with rIL-2 (100 U/ml) for 14 days, CD56⁺ T cells expanded up to 25% of T cells. CD57⁺ T cells were never expanded by these in vitro cultures. The expansion of γδ T cells (mainly Vγ9^? non-adult type) also occurred in the in vitro culture. A considerable proportion of CD56⁺ T cells was found to use Vα24 (i.e. equivalent to invariant Vα14 chain used by murine NK T cells) for TCR αβ. These results suggest that neonatal blood contains only a few NK T cells but CD56⁺ NK T cells and γδ T cells are able to expand in vitro.     

Fine antigen specificity of human γδ T cell lines (Vγ9+) established by repetitive stimulation with a serotype (KTH-1) of a gram-positive bacterium,Streptococcus sanguis

We have established human γδ T cell lines specific for Streptococcus sanguis (S. sanguis) KTH-1 present in normal oral cavity flora. The CD4^?CD8^? CD3⁺Vγ9⁺Vδ1^?CD45RO⁺ CD25⁺ T cell lines showed a proliferative response to the streptococcal antigen (Ag) in the presence of autologous antigen-presenting cells without apparent evidence of HLA restriction. The proliferative response of the γδ T cell lines was completely blocked by anti-TcRγδ monoclonal antibody (mAb) and anti-HLA class I mAb (W6/32), whereas anti-HLA classical class Ia mAb (B-H9; anti-HLA-A,B,C), anti-HLA class II mAb (anti-DR, anti-DQ, and anti-DP) and anti-CD4 mAb did not have any inhibitory effects. Surprisingly, the γδ T cell lines showed the proliferative response against the original bacterial Ag KTH-1 exclusively, and exhibited no cross-reactivity with nominal Ag such as purified protein derivative of tuberculin, tetanus toxoid and Mycobacterium tuberculosis, or the same species but different strain of S. sanguis, American Type Culture Collection (ATCC) standard strain (10556), or even with the same strain but different serotype of S. sanguis, KTH-3. Moreover, cytokine production of the γδ T cell lines was similar to the Th1 pattern [interferon-γ, tumor necrosis factor (TNF)-α and TNF-β]. They also produced interleukin-8 that functions as one of chemoattractants for polymorphonuclear cells. Using direct sequencing technique of the polymerase chain reaction products, we found that junctional diversity of the T cell receptor (TcR) used by the parental KTH-1 specific γδ T cell line and its subclones is rather limited. It is suggested that γδ T cells with canonical TcR could preferentially respond to KTH-1 Ag. Thus, in addition to a broad or cross-reactivity of γδ T cells against phylogenetically conserved stress/heat-shock protein, which is well characterized by others, some peripheral blood γδ T cells could recognize and kill exogenous agents with fine antigenic specificity to protect the body against them.     

γδ T cells are secondary participants in acute graft-versus-host reactions initiated by CD4+ αβT cells

To examine the role of T cell subpopulations in an acute graft-versus-host (GVH) reaction, γδ T cells and αβ T cells expressing one of the two prototypic Vβ gene families were negatively isolated from adult blood samples and injected into allogeneic chick embryos. CD4⁺ αβ T cells expressing either Vβ1 or Vβ2 receptors were equally capable of inducing acute GVH reactions, consistent with the idea that αβ T cell alloreactivity is determined by CDR3 variability. By themselves, the γδ T cells were incapable of inducing GVH reactions. However, host γδ T cells were recruited into the donor αβ T cell-initiated lesions, where they were activated and induced to proliferate. The data suggest that γβ T cells may play a secondary role in GVH reactions.     

Interleukin‐18 activates Vγ9Vδ2+ T cells from HIV‐positive individuals: recovering the response to phosphoantigen

The study aimed to identify an immunoregulatory factor that restores the phosphoantigen response of Vγ9Vδ2⁺ T cells from HIV‐positive individuals on antiretroviral therapy. It was designed to characterize the effects of interleukin‐18 (IL‐18) on proliferation and effector function in Vγ9Vδ2 T cells from HIV‐negative individuals and test whether exogenous IL‐18 reconstitutes the Vγ9Vδ2 T‐cell response to phosphoantigen from HIV‐positive donors. Vγ9Vδ2 T cells from HIV‐negative individuals responded strongly to phosphoantigen or aminobisphosphonate stimulation of peripheral blood mononuclear cells (PBMC), whereas cells with similar T‐cell receptor profiles from HIV‐positive individuals only responded to aminobisphosphonate. Interleukin‐18 was higher after aminobisphosphonate stimulation due to activation of the inflammasome pathway. Both IL‐18 and IL‐18 receptor levels were measured and the activity of exogenous IL‐18 on HIV‐negative and HIV‐positive PBMC was evaluated in terms of Vγ9Vδ2 T‐cell proliferation, memory subsets, cytokine expression and CD107a expression. Interleukin‐18 stimulation increased proliferation, enhanced the accumulation of effector memory cells, and increased expression of cytotoxic markers in HIV‐negative controls. When Vγ9Vδ2 T cells from HIV‐positive individuals were stimulated with isopentenyl pyrophosphate in the presence of IL‐18, there was increased proliferation, accumulation of memory cells, and higher expression of CD56, NKG2D and CD107a (markers of cytotoxic effector phenotype). Interleukin‐18 stimulation specifically expanded the Vγ9‐JγP⁺ subset of Vγ9Vδ2 T cells, as was expected for normal responses to phosphoantigen. Interleukin‐18 is a potent stimulator of Vγ9Vδ2 T‐cell proliferation and effector function. Therapies directed at reconstituting Vγ9Vδ2 T‐cell activity in HIV‐positive individuals should include stimulators of IL‐18 or direct cytokine supplementation.     

The surface epithelium of recurrent infected palatine tonsils is rich in γδ T cells

Using a large panel of MoAbs in quantitative morphometric analysis of immunohistochemically stained tissue sections, we compared the frequency and distribution of immune cells in palatine tonsils from patients with recurrent tonsillitis (RT) and patients with idiopathic tonsillar hypertrophy (ITH). We found that differences between the two patient groups in leucocyte populations were limited to the surface epithelium, whereas the cellular composition of interfollicular and follicular areas was similar. Most intraepithelial lymphocytes were CD8⁺ T cells in both groups. However, the number of intraepithelial T cells was significantly higher in RT compared with ITH. This was due to a selective increase in the number of intraepithelial CD8⁺γδ T cells utilizing Vδ1 and Vγ9. In both patient groups the majority of the intraepithelial γδ T cells expressed Vδ1 and Vγ9. Subepithelially, γδ T cells utilizing Vγ9 dominated over cells utilizing Vγ8, while equal proportions expressed Vδ1 and Vδ2. These results suggest that cells utilizing the otherwise rare combination Vδ1/Vγ9 in their T cell receptors (TCR) may constitute a major γδ T cell population in palatine tonsils and are probably reactive to antigens specific to the tonsillar milieu. Furthermore, they indicate that preferentially this γδ T cell subpopulation is involved in immune reactions within the surface epithelium in RT. We speculate that γδ T cells are involved in clearing infectious bacteria at the tonsillar surface and in limiting inflammatory responses in the tonsils. Both local expansion and infiltration of blood cells probably contribute to the high numbers of γδ T cells in RT patients.     

Mycobacteria-reactive γδ T cells in HIV-infected individuals: lack of Vγ9 cell responsiveness is due to deficiency of antigen-specific CD4 T helper type 1 cells

Human γδ T lymphocytes expressing the variable T cell receptor elements Vγδ paired with Vδ2 are activated by antigen derived from Mycobacterium tuberculosis (M. tb.) and presented by antigen-presenting cells (APC). The subsequent proliferation is strictly dependent on the presence of CD4⁺TCRαβ⁺ T helper type 1 (Th1) cells producing interleukin-2 (IL-2). In this study, we report that the reactivity of Vγ9 cells to M. tb. stimulation in vitro was drastically decreased or absent in the majority of the analyzed HIV-1-infected individuals (CDC stages III and IV). We show that the failure of Vγ9 cells frim HIV^? individuals to proliferate following M. tb. stimulation was not due to an intrinsic qualitative or quantitative defect of γδ T cells but rather to a deficiency of M. tb.-reactive CD4 Th1 cells. Thus, Vγ9 responsiveness could be restored if cultures of M. tb.-stimulated T cells from HIV⁺ donors were reconstituted with one of the following: (i) exogenous IL-2; (ii) purified CD4T cells from allogeneic donors; or (iii) T cell-depleted APC from allogeneic donors. In the majority of HIV⁺ patients, the defective Th1 activity of M. tb.-stimulated CD4 T cells could be increased neither by cytokines known to favor Th1 development (IL-12, interferon-γ) nor by neutralization of the Th1-suppressing Th2 cytokine IL-10. We suggest that measurement of Vγ9 cell expansion within M. tb.-stimulated peripheral blood mononuclear cells provides a sensitive assay for the functional capacity of antigen (M. tb.)-specific CD4 Th1 cells in HIV-infected individuals.     

Human peripheral blood γδ T cells are uniformly sensitive to destruction by the lysosomotropic agents leucine methyl ester and leucyl leucine methyl ester

Treatment of peripheral blood mononuclear cells (PBMC) with the lysosomotropic agent leucine methyl ester (Leu-OMe) eliminates monocytes/macrophages and cytotoxic lymphocytes including CD3^? CD16⁺ natural killer (NK) cells and a fraction of T cell receptor (TcR)αβ⁺ CD8⁺ T cells. We report that freshly isolated peripheral blood γδ T cells are highly sensitive to Leu-OMe treatment as well. After incubation of PBMC with 5 mM Leu-OMe or incubation of purified T cells with 50 μ.M leucyl leucine methyl ester (Leu-Leu-OMe) and subsequent overnight culture, CD3^?CD16⁺ NK cells and γ^δ T cells were no longer detectable by immunofluorescence analysis. The two major γ^δ T cell subsets Vγ9⁺Vδ2⁺ and Vγ9-Vδ1⁺ were equally susceptible to Leu-OMe and Leu-Leu-OMe treatment. The elimination of Vγ9⁺ T cells by Leu-OMe treatment was confirmed in functional assays. Stimulation of peripheral blood T cells with killed mycobacteria resulted in selective expansion of Vγ9⁺ T cells. In contrast, no activation of γ^δ T cells was elicited in Leu-OMe-treated responder T cells stimulated with killed mycobacteria.     

Functional and molecular characterization of B cell-responsive Vδ1+ γδ T cells

Cells expressing the Vδ1⁺ gene segment are a minor γδ T cell population in human peripheral blood but predominate in epithelia and (inflamed) tissues. The characteristic dendritic-like morphology of these γδ T cells is consistent with their putative immune surveillance role in epithelia. Their function, however, remains unknown. We and others previously reported that a subset of Vδ1⁺ γδ T cells proliferates after stimulation with Epstein-Barr virus (EBV)-transformed B lymphoblastoid cell lines (LCL), but not with fresh peripheral blood-derived B cells. These responses were independent of the type of T cell receptor (TcR) γ chain co-expressed with the Vδ1 chain. The in vivo relevance of this LCL-mediated activation as well as the nature of the stimulatory ligand on the LCL is not well established. In this study, we tested the proliferative response of Vδ1⁺ LCL-responsive T cells against non-EBV-transformed B cells, activated through CD40 by murine EL4 B5 cells, and to a panel of B cell lines differing in the expression of EBV nuclear antigen proteins and adhesion/co-stimulatory molecules. The role of the Epstein-Barr virus-derived antigen in the induction of this response could be excluded as the activated (non-EBV-transformed) peripheral blood B cells were also able to induce a proliferative response in the LCL-responsive Vδ1⁺ T cells. Therefore, the stimulatory ligand on B cells is of cellular rather than of viral origin, and its expression is up-regulated upon activation of B cells. The expression of B7 and CD39 molecules on the surface of activated B cells appeared to be crucial since antibodies to these structures could block the induction of proliferation of the Vδ1⁺ T cells. Finally, we investigated the diversity of the responding Vδ1⁺ γδ T cell clones by sequence analysis of the TcRδ junctional regions. No restricted V-D-J sequences were found among the LCL-responsive Vδ1⁺ T cell clones, arguing strongly against a mono- or oligoclonal Vδ1⁺ γδ T cell response to LCL. These findings may explain the presence of polyclonally activated Vδ1⁺ T cells in inflamed tissues where activated B cells are often present.     

Mechanisms determining cell membrane expression of different γδ TCR chain pairings

We investigated the ability of the most common TCR‐γ and δ chains to express on the cell surface. Vγ1Cγ4 and Vγ7Cγ1 chains paired with all TCR‐δ chains tested, whereas Vγ4Cγ1 chains were found with Vδ4 and Vδ5, but not with Vδ2 or Vδ6 chains, and Vγ2Cγ2 chains were expressed only with Vδ5. Mapping studies showed that up to four polymorphic residues influence the different co‐expressions of Vγ1 and Vγ2 chains with Vδ chains. Unexpectedly, these residues are not located in the canonical γ/δ interface, but in the outer part of the γδ TCR complex exposed to the solvent. Expression of functional Vδ4 or Vδ6 chains in Vγ2/Vδ5⁺ cells or of functional Vγ2Cγ2 in Vγ1⁺ cells reduced cell‐surface expression of the γδ TCR. Taken together, these data show that (i) the Vγ/Vδ repertoire of mouse γδ T cells is reduced by physical constraints in their associations. (ii) Lack of Vγ2/Vδ expression is due to the formation of aberrant TCR complexes, rather than to an intrinsic inability of the chains to pair and (iii) despite not being expressed at the cell surface, the presence of a functionally rearranged Vγ2 chain in γδ T cells results in reduced TCR levels.     

γδ T cells support gut Ag‐reactive colitogenic effector T‐cell generation by enhancing Ag presentation by CD11b+ DCs in the mesenteric LN

T cells expressing the γδ TCR are dominant T‐cell subsets in the intestinal immune system. We previously demonstrated that γδ T cells play important roles in augmenting Th17‐type colitogenic immune responses in a T‐cell‐induced colitic inflammation model. However, its underlying mechanism remains poorly understood. In this study, an in vitro coculture system using effector T cells enriched in gut Ag‐reactive cells was employed as a readout tool to search for gut Ag presenting APCs. We found that the presence of γδ T cells dramatically enhances gut Ag presentation within the mLN in mice. Gut Ag presentation by CD11b⁺ DC subsets was particularly controlled by γδ T cells. Interestingly, γδ T‐cell entry to the lymph nodes was essential to improve the Ag presentation. Therefore, our results highlight that γδ T cells play a previously unrecognized role to support colitogenic immunity by regulating gut Ag presentation in the draining LN.