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.     

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.     

Control of self-reactive cytotoxic T lymphocytes expressing γδ T cell receptors by natural killer inhibitory receptors

The majority of peripheral blood γδ T cells in human adults expresses T cell receptors (TCR) with identical V regions (Vγ9 and Vδ2). These Vγ9Vδ2 T cells recognize the major histocompatibility complex (MHC) class I-deficient B cell line Daudi and broadly distributed nonpeptidic antigens present in bacteria and parasites. Here we show that unlike αβ or Vγ9^? γδ T cells, the majority of Vγ9Vδ2T cells harbor natural killer inhibitory receptors (KIR) (mainly CD94/NKG2A heterodimers), which are known to deliver inhibitory signals upon interaction with MHC class I molecules. Within Vγ9δ2 T cells, KIR were mainly expressed by clones exhibiting a strong lytic activity against Daudi cells. In stark contrast, almost all Vγ9Vδ2 T cell clones devoid of killing activity were KIR^?, thus suggesting a coordinate acquisition of KIR and cytotoxic activity within Vγ9Vδ2 T cells. In functional terms, KIR inhibited lysis of MHC class I-positive tumor B cell lines by Vγ9Vδ2 cytotoxic T lymphocytes (CTL) and raised their threshold of activation by microbial antigens presented by MHC class I-positive cells. Furthermore, masking KIR or MHC class I molecules revealed a TCR-dependent recognition by Vγ9Vδ2 CTL of ligands expressed by activated T lymphocytes, including the effector cells themselves. Taken together, these results suggest a general implication of Vγ9Vδ2 T cells in immune response regulation and a central role of KIR in the control of self-reactive γδ CTL.     

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.     

Characteristics of fetal thymus-derived T cell receptor γδ intestinal intraepithelial lymphocytes

We have previously demonstrated that grafting of CBF1(H-2^b/d) fetal thymus (FTG) under the kidney capsule of congenitally athymic nude mice of BALB/c background (H-2^d) generates a substantial number of T cell receptor (TCR) γδ intestinal intraepithelial lymphocytes (IEL) that were of FTG origin (H-2^b+) (see accompanying report). Here we investigated the characteristics of these FTG-derived TCR γδ IEL and compared them to the extrathymically derived TCR γδ IEL found in nude mice. Phenotypically, FTG-derived TCR γδ IEL were similar to their extrathymically derived counterparts in that most were Thy-1 ^?, CD5^? and CD8αα (homodimer). Vγ and Vδ gene usage in thymus-derived and extrathymically derived TCR γδ IEL were found to be virtually the same. Functionally, FTG-derived TCR γδ IEL were similar to the TCR γδ IEL found in euthymic mice as both were relatively anergic to TCR cross-linking in vitro. However, FTG-derived TCR γδ IEL differed slightly from extrathymically derived TCR γδ IEL, which were completely nonresponsive to the same in vitro stimulation. Overall, these findings support the view that FTG-derived and extrathymically derived TCR γδ IEL are almost indistinguishable. Lastly, we demonstrate that despite their thymic origin, development of FTG-derived TCR γδ IEL partially takes place extrathymically; that is positive selection of FTG-derived Vδ4 IEL occurs extrathymically. In addition, we demonstrate that the CD8 molecule is not necessary for development and homing of FTG-derived TCR γδ IEL. This later finding suggests that the CD8αα molecule develops extrathymically for FTG-derived CD8αα TCR γδ IEL.     

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.     

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.     

Expansion of the CD4−, CD8− γδ T cell subset in the spleens of mice during non-lethal blood-stage malaria

Splenic γδ T cells (CD4^?, CD8^?) increased more that 10-fold upon resolution of either Plasmodium chabaudi adami or P. c. chabaudi infections in C57BL/6 mice compared to controls. Similarly, a 10- to 20-fold expansion of the γδ T cell population was observed in β₂-microglobulin deficient (β²-m^0.0) mice that had resolved P. c. adami, P. c. chabaudi or P. yoelii yoelii infections. In contrast, increases in the number of splenic αβ T cells in these infected mice were only two to three-fold indicating a differential expansion of the γδ T cell subset during malaria. Because nucleated cells of β₂-m^0/0 mice lack surface expression of major histocompatibility complex class I and class Ib glycoproteins, our findings suggest that antigen presentation by these glycoproteins is not necessary for the increasing number of γδ T cells. Our observation that after resolution of P. c. adami malaria, C57BL/6 mice depleted of CD8⁺ cells by monoclonal antibody treatment had lower numbers of γδ T. cells than untreated controls suggests that the demonstrated lack of CD8⁺ cells in β₂-m^0/0 mice does not contribute to the expansion of the γδ T cell population during non-lethal malaria.     

CD4-negative cytotoxic T cells with a T cell receptor α/βintermediate expression in CD8-deficient mice

Targeted disruption of the CD8 gene results in a profound block in cytotoxic T cell (CTL) development. Since CTL are major histocompatibility complex (MHC) class I restricted, we addressed the question of whether CD8–/– mice can reject MHC class I-disparate allografts. Studies have previously shown that skin allografts are rejected exclusively by T cells. We therefore used the skin allograft model to answer our question and grafted CD8–/– mice with skins from allogeneic mice deficient in MHC class II or in MHC class I (MHC-I or MHC-II-disparate, respectively). CD8–/– mice rejected MHC-I-disparate skin rapidly even if they were depleted of CD4⁺ cells in vivo (and were thus deficient in CD4⁺ and CD8⁺ T cells). By contrast, CD8+/+ controls depleted of CD4⁺ and CD8⁺ T cells in vivo accepted the MHC-I-disparate skin. Following MHC-I, but not MHC-II stimulation, allograft-specific cytotoxic activity was detected in CD8–/– mice even after CD4 depletion. A population expanded in both the lymph nodes and the thymus of grafted CD8–/– animals which displayed a CD4^?8^?3^intermediateTCRα/β^intermediate phenotype. Indeed its T cell receptor (TCR) density was lower than that of CD4⁺ cells in CD8–/– mice or of CD8⁺ cells in CD8+/+ mice. Our data suggest that this CD4^?8^?T cell population is responsible for the CTL function we have observed. Therefore, MHC class I-restricted CTL can be generated in CD8–/– mice following priming with MHC class I antigens in vivo. The data also suggest that CD8 is needed to up-regulate TCR density during thymic maturation. Thus, although CD8 plays a major role in the generation of CTL, it is not absolutely required.     

Murine T Cell Determination of Pregnancy Outcome: I. Effects of Strain, αβ T Cell Receptor, γδ T Cell Receptor,and γδ T Cell Subsets

PROBLEM: T cells bearing αβ T cell receptor (TcR) and γδ TcR are present at the fetomaternal interface, and the latter, which express surface activation markers, can react with fetal trophoblast cell antigens. What is the role of these cells? METHOD: Using stress-abortion-prone DBA/2-mated CBA/J and abortion-resistant C57/B16 mice, αβ, γδ, and CD8^+/- T cell subsets were measured in spleen and uterine decidua. The effect of immunization against abortion and administration of anti-TcR antibody in vivo was examined. Cytokine synthesis was measured by intracellular staining of Brefeldin A-treated cells. RESULTS: Abortion-prone matings showed an unexpected accumulation of γδ T cells beginning in the peri-implantation period and this was suppressed by immunization against abortion. The immunization deleted γδ T cells producing the abortogenic cytokines, TNF-α and γ-interferon, and increased production of the anti-abortive cytokines, IL-10 and transforming growth factor-β2 (TGF-β2). Immunization also boosted the number of αβ T cells which were present in the decidua as early as 2 days after implantation. In vivo injection of GL4 (anti-δ) depleted γδ T cells producing Th1 cytokines in the peri-implantation period, and prevented abortions, whereas H57 (anti-β) decreased the number of αβ T cells and led to 100% abortions. CD8⁺ T cells present in peri-implant decidua before onset of abortions were mostly αβ TcR⁺, although some were γδ⁺. Changes in γδ and αβ T cells in pregnancy were most dramatic in uterine tissue. CONCLUSION: Although decidual γδ T cells after formation of a distinct placenta and fetus produce anti-abortive TGF-β2-like molecules and IL-10, prior events can lead to abortion. High local production of TNF-α and γ-interferon develop during the peri-implantation phase because of an excessive increase in the Th1 cytokine⁺ subset of γδ cells; these cytokines may be contributed by other tissues in decidua, and the contribution of bioactive factors by γδ T cells may augment the cytokine pool. In contrast, αβ T cells (which may be inactivated by stress that causes abortions) may mediate the anti-abortive effect of alloimmunization. Alloimmunization involves a shift from a Th1 to a Th2 pattern in the γδ T cells in decidua.     

Changes in thymic export of γδ and αβ T cells during fetal and postnatal development

The thymus plays an essential role in the generation and selection of T cells and exports approximately 0.5–1% of thymocytes per day in young animals and considerably fewer in older animals. To date there have been no studies directly examining fetal thymic export in any species. Using the technique of intrathymic injection of fluorescein isothiocyanate, followed by an assay for green fluorescent cells in the periphery and for the expression of cell surface antigens on these cells, we have compared directly the export of T cells from the fetal and postnatal ovine thymus. While the thymus exports both αβ and γδ T cells, our results demonstrate that the proportion of thymic γδ T cells that are exported per day is much higher than that of thymic αβ T cells. Moreover, the export rate of γδ T cells increased from approximately 1 in every 60 γδ thymocytes per day emigrating from the fetal thymus to 1 in every 20 from the postnatal thymus. In addition, we identify a population of CD5⁺CD4^?CD8^?γδ^? T cells emigrating from the fetal thymus but greatly reduced among thymic emigrants after birth. These findings have several implications regarding the mechanisms and control of selection of both γδ and αβ T cells.     

Increased Expression of Cell Surface Markers on Endometrial γδ T-Cell Receptor+ Intraepithelial Lymphocytes Induced by the Local Presence of the Sheep Conceptus

PROBLEM: In sheep, γδ T-cell receptor (TCR)⁺ cells are a major lymphocyte subpopulation in the luminal epithelium of the uterine endometrium. During late pregnancy, this population of T cells increases in number and becomes more granulated. This study was performed to determine whether this apparent activation was induced by local effects of the conceptus or systemic effects of pregnancy. METHODS: The unilaterally-pregnant ewe, in which the conceptus is surgically confined to one uterine horn, was used to distinguish between systemic and local effects of pregnancy on function of endometrial γδ TCR⁺ intraepithelial lymphocytes. Lymphocytes collected from peripheral blood, and from the endometrial luminal epithelium of cyclic and unilaterally-pregnant ewes (day 140 of gestation) were analyzed by flow cytometry. RESULTS: As compared to γδ TCR⁺ lymphocytes in peripheral blood, γδ TCR⁺ intraepithelial lymphocytes from non-pregnant ewes had a lower percentage of cells staining positive for CD25, CD44, and L-selectin. There was no effect of pregnancy on the percentage of γδ TCR⁺ peripheral blood lymphocytes staining positive for CD25, CD44, CD29, or L-selectin. Similarly, the percentage of intraepithelial lymphocytes staining positive for these antigens was similar for cells collected from cyclic ewes and cells from the nonpregnant uterine horn of unilaterally-pregnant ewes. In contrast, there was a higher percentage of CD25, CD44, CD29, and L-selectin⁺ cells for γδ TCR⁺ intraepithelial lymphocytes from the conceptus-containing uterine horn of pregnant ewes than for γδ TCR⁺ intraepithelial lymphocytes from the endometrium of cyclic ewes or from the nonpregnant uterine horn of pregnant ewes. CONCLUSION: The local presence of the conceptus causes changes in cell surface marker expression on endometrial γδ TCR⁺ intraepithelial lymphocytes during pregnancy. These changes may reflect conceptus-induced activation of this population of cells.     

Lymphocytes bearing the γδ T cell receptor in acute Brucella melitensis infection

A phenotypical analysis carried out by indirect immunofluorescence and two-color cytofluorometry showed that the number of lymphocytes bearing the γδ T cell receptor (TcR) heterodimer was dramatically increased in the blood of six children with Brucella melitensis infection. Most in vivo expanded γδ T cells reacted with a monoclonal antibody which identifies Vδ2 gene products and a significant proportion expressed CD25 and HLA-DR activation antigens. In addition, whereas only a few γδ T lymphocytes were CD8⁺, nearly all were CD4^?. Highly enriched populations of both αβ and γδ T cells were obtained by negative immunoselection from three subjects with brucellosis sampled during convalescence. Despite the different form of their TcR, the proliferation of these two major T cell subsets in response to a mitogenic anti-CD3 monoclonal reagent (OKT3) was optimal. In contrast, αβ, but not γδ, T lymphocytes proliferated vigorously in response to the antigenic stimulus elicited by heat-killed Brucella. Further studies are, therefore, needed to determine whether the selective expansion of the γδ T cell subpopulation observed during the clinical course of the infection is driven by antigenic determinant(s) borne by the pathogen in vivo or is due to host-derived stimuli, such as autologous heat-shock proteins expressed on the surface of the infected cells.     

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.     

Comparative analysis of αβ and γδ T cell activation by Mycobacterium tuberculosis and isopentenyl pyrophosphate

Phosphorylated nonpeptide compounds have recently been identified as potent mycobacteria-derived ligands for human Vγ9/Vδ2-expressing γδ T cells. Crude mycobacterial extracts also contain protein antigens which stimulate CD4 αβ T cells to produce growth factors that are used by γδ T cells for clonal expansion. We have investigated the dynamics in vitro of expansion of CD4 T cells and Vγ9 cells in cultures of peripheral blood mononuclear cells stimulated with synthetic isopentenyl pyrophosphate (IPP) in the absence or presence of additional stimuli. The results indicated that following stimulation with IPP, γδ T cells express CD25 and CD69 antigens, but fail to proliferate unless growth factors are provided exogenously or endogenously through activation of CD4 T cells by additional stimuli such as tetanus toxoid, alloantigen, or superantigens. Furthermore, the presence of antigen presenting cells are required for expansion of γδ T cells. In response to IPP stimulation, purified CD4 T cells neither express CD25 or CD69, nor do they proliferate even in the presence of exogenous IL-2. Apart from IL-2, IL-15 and, less efficiently, IL-4, IL-7, and IL-12 can contribute to cellular expansion of IPP-reactive Vγ9 cells. Together, the results demonstrate that peripheral blood γδ T cells proliferate in response to IPP only if CD4 T cells are simultaneously activated by an additional stimulus. This mechanism provides a tight control of the reactivity of γδ T cells towards phosphorylated nonpeptide antigens.     

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 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.