Crosstalk between alpha/beta T cells and gamma/delta T cells in vivo: activation of alpha/beta T-cell responses after gamma/delta T-cell modulation with the monoclonal antibody GL3

Inhibition of γδ-TcR or IL17a Reduces T-Cell and Neutrophil Infiltration after Ischemia/Reperfusion Injury in Mouse Liver

Neutrophil and T-cell recruitment contribute to hepatic ischemia/reperfusion injury. The initial inflammatory response is orchestrated by Kupffer cells and liver sinusoid endothelial cells. However, other cell types, including γδ-Τ cells, seem to be key mediators in further inflammatory cell recruitment and proinflammatory cytokine release, including IL17a. In this study, we used an in vivo model of partial hepatic ischemia/reperfusion injury (IRI) to investigate the role of the γδ-Τ-cell receptor (γδTcR) and the role of IL17a in the pathogenesis of liver injury. Forty C57BL6 mice were subjected to 60 min of ischemia followed by 6 h of reperfusion (RN 6339/2/2016). Pretreatment with either anti-γδΤcR antibodies or anti-IL17a antibodies resulted in a reduction in histological and biochemical markers of liver injury as well as neutrophil and T-cell infiltration, inflammatory cytokine production and the downregulation of c-Jun and NF-κΒ. Overall, neutralizing either γδTcR or IL17a seems to have a protective role in liver IRI.

B Cell and CD4 T Cell Interactions Promote Development of Atherosclerosis

Interaction between B and CD4 T cells is crucial for their optimal responses in adaptive immunity. Immune responses augmented by their partnership promote chronic inflammation. Here we report that interaction between B and CD4 T cells augments their atherogenicity to promote lipid-induced atherosclerosis. Genetic deletion of the gene encoding immunoglobulin mu (μ) heavy chain (μMT) in ApoE^−/− mice resulted in global loss of B cells including those in atherosclerotic plaques, undetectable immunoglobulins and impaired germinal center formation. Despite unaffected numbers in the circulation and peripheral lymph nodes, CD4 T cells were also reduced in spleens as were activated and memory CD4 T cells. In hyperlipidemic μMT^−/− ApoE^−/− mice, B cell deficiency decreased atherosclerotic lesions, accompanied by absence of immunoglobulins and reduced CD4 T cell accumulation in lesions. Adoptive transfer of B cells deficient in either MHCII or co-stimulatory molecule CD40, molecules required for B and CD4 T cell interaction, into B cell-deficient μMT^−/− ApoE^−/− mice failed to increase atherosclerosis. In contrast, wildtype B cells transferred into μMT^−/− ApoE^−/− mice increased atherosclerosis and increased CD4 T cells in lesions including activated and memory CD4 T cells. Transferred B cells also increased their expression of atherogenic cytokines IL-1β, TGF-β, MCP-1, M-CSF, and MIF, with partial restoration of germinal centers and plasma immunoglobulins. Our study demonstrates that interaction between B and CD4 T cells utilizing MHCII and CD40 is essential to augment their function to increase atherosclerosis in hyperlipidemic mice. These findings suggest that targeting B cell and CD4 T cell interaction may be a therapeutic strategy to limit atherosclerosis progression.

Genetic models reveal origin, persistence and non-redundant functions of IL-17-producing γδ T cells

The authors present a genetic mouse model for conditional depletion of γδ T cells, confirming the fetal origin and persistence of Tγδ17 cells. They show differential phenotypes after acute depletion versus constitutive γδ T cell deficiency in imiquimod-induced psoriasis.

γδ T cells are highly conserved in jawed vertebrates, suggesting an essential role in the immune system. However, γδ T cell–deficient Tcrd^−/− mice display surprisingly mild phenotypes. We hypothesized that the lack of γδ T cells in constitutive Tcrd^−/− mice is functionally compensated by other lymphocytes taking over genuine γδ T cell functions. To test this, we generated a knock-in model for diphtheria toxin–mediated conditional γδ T cell depletion. In contrast to IFN-γ–producing γδ T cells, IL-17–producing γδ T cells (Tγδ17 cells) recovered inefficiently after depletion, and their niches were filled by expanding Th17 cells and ILC3s. Complementary genetic fate mapping further demonstrated that Tγδ17 cells are long-lived and persisting lymphocytes. Investigating the function of γδ T cells, conditional depletion but not constitutive deficiency protected from imiquimod-induced psoriasis. Together, we clarify that fetal thymus-derived Tγδ17 cells are nonredundant local effector cells in IL-17–driven skin pathology.

γδT cells regulate chronic airway inflammation and development of airway remodelling

BACKGROUND

γδT cells play a crucial immunoregulatory role in the lung, maintaining normal airway tone and preventing hyperresponsiveness to innocuous allergen. During acute inflammatory episodes, γδT cells promote resolution of acute inflammation. However, their contribution to inflammation-associated airway remodelling remains unexplored. Here we investigate the effects of γδT cell blockade on established allergic airway inflammation and development of remodelling.

METHODS

Sensitised mice were exposed to prolonged ovalbumin challenge or continuous house-dust mite exposure to induce chronic inflammation and remodelling. Functional blocking anti-TCRδ antibody was administered therapeutically, and parameters of airway inflammation and remodelling were examined.

RESULTS

Therapeutic blockade of γδT cells prevented the typical resolution of acute airway inflammation characterised by elevated eosinophil and Th2 cell numbers. Moreover, the lung displayed exacerbated airway remodelling, typified by excess peribronchiolar collagen deposition.

CONCLUSIONS

These results demonstrate a unique role for γδT cells in constraining allergen-induced airway remodelling. Manipulating the γδT cell compartment may therefore contribute to strategies to prevent and treat remodelling.

γδ T cell and other immune cells crosstalk in cellular immunity

γδ T cells have been recognized as effectors with immunomodulatory functions in cellular immunity. These abilities enable them to interact with other immune cells, thus having the potential for treatment of various immune-mediated diseases with adoptive cell therapy. So far, the interactions between γδ T cell and other immune cells have not been well defined. Here we will discuss the interactivities among them and the perspective on γδ T cells for their use in immunotherapy could be imagined. The understanding of the crosstalk among the immune cells in immunopathology might be beneficial for the clinical application of γδ T cell.

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.

Regulatory effect of gammadelta T cells on IL-17+ uveitogenic T cells

PURPOSE

To characterize the regulatory effect of gammadelta T cells in the activation of IL-17+ uveitogenic T cells.

METHODS

The authors administered the gammadelta TCR-specific antibody GL3 to B6 mice before or after antigen immunization and examined Th1- or Th17-polarized T-cell responses. The intensity of Th17 responses was also examined in responder T cells containing varying numbers of gammadelta T cells.

RESULTS

GL3 treatment resulted in varying degrees of depletion of circulating gammadelta T cells, depending on when the antibody was administered. The intensity of the alphabetaTCR+IL-17+, but not the alphabetaTCR+IFN-gamma+, IRBP-specific T-cell responses was correlated to the percentage of gammadelta T cells in the responder T cells. Kinetic studies showed that early IL-17+ T cells were primarily gammadelta T cells, with a later gradual shift to alphabeta T cells. A close association was seen between the intensity of the IL-17+ autoreactive T-cell response and the percentage of gammadelta T cells in the responder T cells. Although a modest increase in gammadelta T cells among the responder T cells promoted the expansion of IL-17+ alphabetaTCR+ T cells, a higher proportion of gammadelta T cells inhibited it.

CONCLUSIONS

gammadelta T cells are actively involved in the generation of alphabetaTCR+IL-17+ T cells. The number of gammadelta T cells and the alphabeta/gammadelta T-cell ratio in the responder T cells regulate the intensity of the Th17-type autoreactive T-cell response.

Human peripheral gammadelta T cells possess regulatory potential

Deficiency in gammadelta T cells aggravates colitis in animal models suggesting that gammadelta T cells have regulatory properties. Therefore, proliferation, suppression and cytokine secretion of human gammadelta T cells were determined in vitro. Human peripheral gammadelta T cells were isolated from the whole blood of healthy donors by magnetic antibody cell sorting technology. The proliferation after CD3/CD28 stimulation was measured by (3)[H]thymidine incorporation. Interferon-gamma (IFN-gamma), interleukin-2 (IL-2), transforming growth factor-beta (TGF-beta) and IL-10 concentrations were measured by enzyme-linked immunosorbent assay; TGF-beta messenger RNA was also measured by reverse transcription-polymerase chain reaction. The expression of latency associated peptide (LAP), a TGF-beta complex component, intracellular cytokine content and T helper cell proliferation were measured by flow cytometry. Human gammadelta T cells showed poor proliferation upon CD3/CD28 stimulation and suppressed T helper cell growth stronger than CD4(+) CD25(+) T cells, although gammadelta T cells were FOXP3 negative. They secreted little IL-2 but high concentrations of IFN-gamma, IL-10 and TGF-beta. When looking at LAP expression the Vdelta1 subset was found to be the main TGF-beta producer compared to Vdelta2 T cells. Taken together, peripheral gammadelta T cells have in vitro a more potent regulatory potential than CD4(+) CD25(+) cells regarding T helper cell suppression. This is most likely the result of strong TGF-beta secretion, particularly by the Vdelta1 subset.

Major role of gamma delta T cells in the generation of IL-17+ uveitogenic T cells

We show that in vitro activation of interphotoreceptor retinoid-binding protein (IRBP)-specific T cells from C57BL/6 mice immunized with an uveitogenic IRBP peptide (IRBP(1-20)) under TH17-polarizing conditions is associated with increased expansion of T cells expressing the gammadelta TCR. We also show that highly purified alphabeta or gammadelta T cells from C57BL/6 mice immunized with IRBP(1-20) produced only small amounts of IL-17 after exposure to the immunizing Ag in vitro, whereas a mixture of the same T cells produced greatly increased amounts of IL-17. IRBP-induced T cells from IRBP-immunized TCR-delta(-/-) mice on the C57BL/6 genetic background produced significantly lower amounts of IL-17 than did wild-type C57BL/6 mice and had significantly decreased experimental autoimmune uveitis-inducing ability. However, reconstitution of the TCR-delta(-/-) mice before immunization with a small number of gammadelta T cells from IRBP-immunized C57BL/6 mice restored the disease-inducing capability of their IRBP-specific T cells and greatly enhanced the generation of IL-17(+) T cells in the recipient mice. Our study suggests that gammadelta T cells are important in the generation and activation of IL-17-producing autoreactive T cells and play a major role in the pathogenesis of experimental autoimmune uveitis.

IL-15 produced and trans-presented by DCs underlies homeostatic competition between CD8 and {gamma}{delta} T cells in vivo

Homeostatic mechanism by which peripheral T-cell subsets are maintained in vivo remains largely unknown. Using a T-cell proliferation model under lymphopenic settings, we now demonstrate that gammadelta T cells limit CD8 T-cell expansion but not the initial proliferation after transfer into lymphopenic recipients. Interleukin-15 (IL-15) produced by and trans-presented on the membrane of the CD11c(+) dendritic cells (DCs) is the key factor that mediates homeostatic competition between CD8 and gammadelta T cells, revealing previously unrecognized IL-15-dependent homeostatic mechanisms between different T-cell subsets in vivo.

Differential expression of beta 2-integrins and cytokine production between gammadelta and alphabeta T cells in experimental autoimmune encephalomyelitis

The expression of beta 2-integrins on gammadelta T cells in naïve mice or those with experimental autoimmune encephalomyelitis (EAE) remains poorly characterized. We compared beta 2-integrin expression and cytokine production between gammadelta and alphabeta T cells over the acute course of EAE. We observed that unlike in alphabeta T cells, beta 2-integrin expression on gammadelta T cells increased significantly from baseline, peaked at Day 10, and remained unchanged in the draining lymph nodes or declined in the spleen and CNS by Day 15. In addition, IFN-gamma- and TNF-alpha-producing gammadelta T cells infiltrated the CNS rapidly and produced significantly more of these cytokines than alphabeta T cells throughout the course of EAE. These results suggest unique roles for beta 2-integrins in the trafficking of gammadelta versus alphabeta T cells during EAE and that gammadelta T cells infiltrate the CNS rapidly, producing cytokines, which modulate acute disease.

T cells and cytokines in intracellular bacterial infections: experiences with Mycobacterium bovis BCG

Intracellular bacteria reside in mononuclear phagocytes, and protective immunity is dominated by T lymphocytes. Mycobacterium bovis bacillus Calmette-Guéin (BCG) infection of mice represents an excellent model for studying immune mechanisms involved in defence against persistent intracellular bacteria that cause chronic disease. Gene disruption mutant mice include: A beta-/-, which lack conventional CD4+ T cell receptor alpha/beta (TCR alpha/beta) T lymphocytes; beta 2 microglobulin -/-, which lack conventional CD8+ TCR alpha/beta lymphocytes; TCR beta-/-, which lack all TCR alpha/beta lymphocytes; TCR delta-/-, which lack all TCR gamma/delta lymphocytes; and RAG-1-/- mutants, which lack mature T and B lymphocytes. Studies of these mutants suggest that CD4+ TCR alpha/beta, CD8+ TCR alpha/beta and TCR gamma/delta T lymphocytes all contribute to immunity against M. bovis BCG. Activation of antibacterial effector functions in macrophages by T helper 1 (Th1) cell-derived gamma-interferon (IFN-gamma) is central to protection. In contrast, Th2 cells are only marginally involved. Activation of Th1 and Th2 cells is regulated by interleukin 10 (IL-10) and IL-12, which are induced early in infection with M. bovis BCG. Although IL-12 is stimulated by M. bovis BCG in immunocompetent mice, studies with IFN-gamma receptor-deficient and tumour necrosis factor alpha (TNF-alpha) receptor-deficient mutant mice suggest that M. bovis BCG-induced IL-12 secretion depends on IFN-gamma and TNF-alpha. Hence, IL-12 cannot be the first cytokine produced during M. bovis BCG infection.

Aggravation of intestinal inflammation by depletion/deficiency of gammadelta T cells in different types of IBD animal models

The role of gammadelta T cells in inflammatory bowel disease (IBD) is still controversial. Although gammadelta T cells induce IBD in immunodeficient animals, others suggest a protective role of gammadelta T cells. Therefore, this study was conducted in order to elucidate the effect of gammadelta T cell depletion/deficiency on different IBD animal models. Mice depleted of or deficient in gammadelta T cells were exposed to dextran sodium sulfate (DSS) in order to induce colitis. In addition, gammadelta T cells were depleted in mice with terminal ileitis (TNFDeltaARE) or colitis due to interleukin 2 deficiency (IL-2 ko). Finally, DSS-induced colitis was studied in mice deficient in interferon gamma (IFN-gamma ko) upon gammadelta T cell depletion. Depletion of gammadelta T cells aggravated DSS-induced colitis and terminal ileitis of TNFDeltaARE mice. Exacerbated DSS-induced colitis was also found in gammadelta T cell-deficient mice. IL-2 ko mice showed increased mortality upon early (starting at 4 wk of age) but not late depletion (starting at 8 wk of age). Early gammadelta T cell depletion or deficiency resulted in increased IFN-gamma production by both lamina propria lymphocytes and splenocytes in every model investigated herein. In IFN-gamma ko mice, gammadelta T cell depletion did not affect the development and course of DSS-induced colitis. The protective effect of gammadelta T cells in IBD was confirmed in various IBD animal models. Particularly, during the early phase of intestinal inflammation, gammadelta T cells appear to be important. The mechanism seems to involve the control of IFN-gamma production and epithelial regeneration.

A requirement for the Vgamma1+ subset of peripheral gammadelta T cells in the control of the systemic growth of Toxoplasma gondii and infection-induced pathology

gammadelta T cells are a diverse population of T cells that are widely distributed and are a common feature of pathogen-induced immune responses. It is not clear, however, whether different populations of gammadelta T cells have specific functions, and what factors determine the functional properties of individual populations. A murine model of peroral Toxoplasma gondii infection was used to determine the contribution Vgamma1+ intestinal intraepithelial lymphocytes (IELs) vs systemic Vgamma1+ T cells make to the acute and chronic stages of the host immune response, and whether the macrophage cytocidal activity of Vgamma1+ T cells described in bacterial infections is seen in other, unrelated infectious disease models. In response to oral infection with virulent type 1 or avirulent type II strains of T. gondii, TCR-delta-/- mice rapidly developed severe ileitis. In contrast, in mice deficient in Vgamma1+ T cells and IELs and wild-type mice, inflammation was delayed in onset and less severe. The protective effect of (Vgamma1-) IELs to Toxoplasma infection was unrelated to their cytolytic and cytokine (Th1)-producing capabilities. Systemic Vgamma1+ T cells were shown to play an essential role in limiting parasite growth and inflammation in peripheral tissues and, in particular, in the CNS, that was associated with their ability to efficiently kill parasite-elicited and infected macrophages. These findings suggest that macrophage cytocidal activity of Vgamma1+ T cells may be a universal feature of pathogen-induced immune responses and that microenvironmental factors influence the involvement and function of gammadelta T cells in the host response to infection.

Influence of Bacillus Calmette-Guèrin vaccination at birth and 2 months old age on the peripheral blood T-cell subpopulations [gamma/delta and alpha-beta T cell]

The neonatal immune system is immature and may be affected by Bacillus Calmette-Guèrin (BCG) vaccine. We investigated the influence of BCG given at two different ages on the peripheral blood (PB) T-cell subpopulations. Forty full term healthy newborns were randomly chosen. Twenty of them were vaccinated with BCG at birth (group I) and the remaining at the age of 2 months (group II). The cell analysis were carried out before (pre-BCGI and pre-BCGII), and 2 months after (post-BCGI and post-BCGII) the vaccination. The analysis of the gamma/delta and alpha/beta T-cell receptor (TCR) antigens was done by two-colour flowcytometer. The purified protein derivative (PPD) response was investigated 2 months after vaccination. The results showed that although T-cell (TCR+ cell) counts showed no difference in PB before and after vaccination in both study groups, the total lymphocyte and non-T cell (TCR- cell) populations increased significantly whereas alphabetaT-cell population significantly decreased after vaccination. On the contrary, gammadeltaT-cell counts in PB increased significantly 2 months after vaccination in group I but not in group II. Total lymphocyte and non-T cell counts in vaccinated infants at 2 months of age (post-BCGI) were significantly higher than in unvaccinated infants of the same age whereas alphabetaT-cell count in vaccinated infants was significantly low. However, total T-cell and gammadeltaT-cell counts showed no difference. PPD positivity was similar in both study groups (61% in group I, 66% in group II). Neither alphabetaT- nor gammadeltaT-cell counts were different in PPD positive and PPD negative infants. Our study shows that BCG causes marked quantitative changes in the PB T-cell subpopulations in young infants.

{gamma}{delta} T cell homeostasis is established in competition with {alpha}{beta} T cells and NK cells

gammadelta T cells are a diverse population of lymphocytes that play an important role in immune regulation. The size of the gammadelta T cell pool is tightly regulated, comprising only 1-10% of total lymphoid T cells in mice and humans. We examined the homeostatic regulation of gammadelta T cells using a model of lymphopenia-induced homeostatic expansion. We found that IL-15 and, to a lesser extent, IL-7 play an important role in lymphoid gammadelta T cell homeostasis. Moreover, gammadelta T cell homeostatic expansion was limited not only by gammadelta T cells themselves but also by natural killer cells and alphabeta T cells. Our results suggest that CD8(+) alphabeta T cells are the most potent inhibitors of gammadelta T cell homeostasis and exert their effect by competing for IL-15.

Gamma delta T cells regulate the extent and duration of inflammation in the central nervous system by a Fas ligand-dependent mechanism

Gamma delta T cells have been shown to regulate immune responses associated with inflammation, but the mechanism of this regulation is largely unknown. Using the experimental autoimmune encephalomyelitis (EAE) model of the human CNS autoimmune disease multiple sclerosis, we demonstrate that gamma delta T cells are important regulators of CNS inflammation. This was shown using gamma delta T cell-deficient mice that were unable to recover from EAE. The chronic disease was accompanied by a prolonged presence of both macrophages and lymphocytes in the CNS. This extended inflammatory response was due to alterations in both cell proliferation and death. In mice lacking gamma delta T cells, proliferation of encephalitogenic T cells was 3-fold higher, and caspase activity, indicating apoptosis, was 2-fold lower compared with those in control mice recovering from EAE. gamma delta T cell-deficient mice reconstituted with wild-type gamma delta T cells recovered from EAE and resolved inflammation in the CNS, whereas mice reconstituted with Fas ligand-dysfunctional gamma delta T cells did not. Thus, gamma delta T cells regulate both inflammation in the CNS and disease recovery via Fas/Fas ligand-induced apoptosis of encephalitogenic T cells, and a quick resolution of inflammation in the CNS is essential to prevent permanent damage to the CNS resulting in chronic disease.

Potentiation of immunological tolerance induction in adult mice by co-administration of pooled normal IgG and oral tolerogens: a potential therapeutic approach for autoimmune diseases

Oral tolerance can be defined as the inability of an adult animal to produce specific antibodies or cellular immune responses upon conventional immunization, after oral antigenic administration. Recently, the oral administration of antigens has gained renewed interest because of the possibility of inducing tolerance in nonimmunized adult animals and, consequently, opening up the theoretical possibility of preventing or treating diseases caused by malfunction of the immune system. This strategy has been proven to be useful in the prevention of allergic and autoimmune diseases in rodents, as well as in the amelioration of certain autoimmune diseases in humans. Although there is experimental and clinical evidence for the usefulness of oral tolerance in medical practice, the mechanisms responsible for this phenomenon are still poorly understood, and the results obtained are not always satisfactory. Herein, we show that the thymus is required for the induction and maintenance of oral tolerance, providing evidence that it is not a pure form of clonal deletion-based peripheral tolerance. Oral tolerance could therefore depend on the formation and release to the periphery of regulatory T cells, such as gammadelta or alphabeta T cells, by the thymus. This finding may have profound implications for the treatment of autoimmune diseases, since most of them are associated with thymic hypofunction. On the other hand, due to so far unknown mechanisms, the intraperitoneal co-administration of normal IgG to mice orally treated with tolerogen leads to a sustained and intense immunological tolerance, both in euthymic and thymectomized mice, including those of the lupus erythematosus-prone NZB x NZW lineage. This approach for inducing and maintaining tolerance in thymus-deficient conditions is discussed and put forth herein as a new evidence-based proposition for the therapy of autoimmune diseases.

Gammadelta T cells enhance the expression of experimental autoimmune encephalomyelitis by promoting antigen presentation and IL-12 production

Using an adoptive transfer model of experimental autoimmune encephalomyelitis (EAE) induced by myelin basic protein (MBP)-reactive lymph node cells (LNC), we have shown that depletion of gammadelta T cells from LNC resulted in diminished severity of EAE in recipient mice, both clinically and histopathologically. The reduced potency of gammadelta T cell-depleted LNC to induce EAE correlated with decreased cell proliferation in response to MBP. The gammadelta T cell effect upon the threshold of MBP-induced LNC proliferation and EAE transfer was restored by reconstitution of gammadelta T cells derived from either MBP-immunized or naive mice, indicating that this effect was not Ag specific. The enhancing effect of gammadelta T cells on MBP-induced proliferation and EAE transfer required direct cell-to-cell contact with LNC. The gammadelta T cell effect upon the LNC response to MBP did not involve a change in expression of the costimulatory molecules CD28, CD40L, and CTLA-4 on TCRalphabeta(+) cells, and CD40, CD80, and CD86 on CD19(+) and CD11b(+) cells. However, depletion of gammadelta T cells resulted in significant reduction in IL-12 production by LNC. That gammadelta T cells enhanced the MBP response and severity of adoptive EAE by stimulating IL-12 production was supported by experiments showing that reconstitution of the gammadelta T cell population restored IL-12 production, and that gammadelta T cell depletion-induced effects were reversed by the addition of IL-12. These results suggest a role for gammadelta T cells in the early effector phase of the immune response in EAE.

Innate immune surveillance of spontaneous B cell lymphomas by natural killer cells and gammadelta T cells

Few studies have demonstrated that innate lymphocytes play a major role in preventing spontaneous tumor formation. We evaluated the development of spontaneous tumors in mice lacking β-2 microglobulin (β2m; and thus MHC class I, CD1d, and CD16) and/or perforin, since these tumor cells would be expected to activate innate effector cells. Approximately half the cohort of perforin gene-targeted mice succumbed to spontaneous disseminated B cell lymphomas and in mice that also lacked β2m, the lymphomas developed earlier (by more than 100 d) and with greater incidence (84%). B cell lymphomas from perforin/β2m gene-targeted mice effectively primed cell-mediated cytotoxicity and perforin, but not IFN-γ, IL-12, or IL-18, was absolutely essential for tumor rejection. Activated NK1.1⁺ and γδTCR⁺ T cells were abundant at the tumor site, and transplanted tumors were strongly rejected by either, or both, of these cell types. Blockade of a number of different known costimulatory pathways failed to prevent tumor rejection. These results reflect a critical role for NK cells and γδTCR⁺ T cells in innate immune surveillance of B cell lymphomas, mediated by as yet undetermined pathway(s) of tumor recognition.

V gamma 4+ gamma delta T cells regulate airway hyperreactivity to methacholine in ovalbumin-sensitized and challenged mice

The Vgamma4(+) pulmonary subset of gammadelta T cells regulates innate airway responsiveness in the absence of alphabeta T cells. We now have examined the same subset in a model of allergic airway disease, OVA-sensitized and challenged mice that exhibit Th2 responses, pulmonary inflammation, and airway hyperreactivity (AHR). In sensitized mice, Vgamma4(+) cells preferentially increased in number following airway challenge. Depletion of Vgamma4(+) cells before the challenge substantially increased AHR in these mice, but had no effect on airway responsiveness in normal, nonchallenged mice. Depletion of Vgamma1(+) cells had no effect on AHR, and depletion of all TCR-delta(+) cells was no more effective than depletion of Vgamma4(+) cells alone. Adoptively transferred pulmonary lymphocytes containing Vgamma4(+) cells inhibited AHR, but lost this ability when Vgamma4(+) cells were depleted, indicating that these cells actively suppress AHR. Eosinophilic infiltration of the lung and airways, or goblet cell hyperplasia, was not affected by depletion of Vgamma4(+) cells, although cytokine-producing alphabeta T cells in the lung increased. These findings establish Vgamma4(+) gammadelta T cells as negative regulators of AHR and show that their regulatory effect bypasses much of the allergic inflammatory response coincident with AHR.

Responses of bovine WC1(+) gammadelta T cells to protein and nonprotein antigens of Mycobacterium bovis

WC1(+) gammadelta T cells of Mycobacterium bovis-infected cattle are highly responsive to M. bovis sonic extract (MBSE). In mycobacterial infections of other species, gammadelta T cells have been shown to respond to protein and nonprotein antigens, but the bovine WC1(+) gammadelta T-cell antigenic targets within MBSE require further definition in terms of the dominance of protein versus nonprotein components. The present study sought to characterize the WC1(+) gammadelta T-cell antigenic targets, together with the role of interleukin-2 (IL-2), in the context of M. bovis infection. This was achieved by testing crude and defined antigens to assess protein versus nonprotein recognition by WC1(+) gammadelta T cells in comparison with CD4(+) alphabeta T cells. Both cell types proliferated strongly in response to MBSE, with CD4(+) T cells being the major producers of gamma interferon (IFN-gamma). However, enzymatic digestion of the protein in MBSE removed its ability to stimulate CD4(+) T-cell responses, whereas some WC1(+) gammadelta T-cell proliferation remained. The most antigenic protein inducing proliferation and IFN-gamma secretion in WC1(+) gammadelta T-cell cultures was found to be ESAT-6, which is a potential novel diagnostic reagent and vaccine candidate. In addition, WC1(+) gammadelta T-cell proliferation was observed in response to stimulation with prenyl pyrophosphate antigens (isopentenyl pyrophosphate and monomethyl phosphate). High levels of cellular activation (CD25 expression) resulted from MBSE stimulation of WC1(+) gammadelta T cells from infected animals. A similar degree of activation was induced by IL-2 alone, but for WC1(+) gammadelta T-cell division IL-2 was found to act only as a costimulatory signal, enhancing antigen-driven responses. Overall, the data indicate that protein antigens are important stimulators of WC1(+) gammadelta T-cell proliferation and IFN-gamma secretion in M. bovis infection, with nonprotein antigens inducing significant proliferation. These findings have important implications for diagnostic and vaccine development.

The WC1(+) gammadelta T-cell population in cattle: a possible role in resistance to intracellular infection

Intracellular infections are important in veterinary medicine and detailed understanding of the associated immune responses is needed for optimal development of strategies based on diagnosis and vaccination. It is generally accepted that cell-mediated immune responses are of greatest importance in intracellular infections and recent studies from several bovine models of infection indicate that WC1(+) gammadelta T-cells have a number of possible levels of involvement, which remain incompletely defined. Investigations of experimental infection with Mycobacterium bovis in cattle have indicated that WC1(+) gammadelta T-cells are among the first cells to accumulate at initial sites of infection, an observation which has been linked with decreased numbers of these cells in the circulation within days of infection. These WC1(+) gammadelta T-cells have been shown to respond in vitro, both to protein antigens and to non-protein, phosphate containing antigens of M. bovis and to be capable of producing IFN-gamma. Studies of M. bovis infection in calves depleted of WC1(+) gammadelta T-cells by monoclonal antibody have suggested that the presence of these cells is associated with development of a Th1-biased acquired immune response. In combination, these observations allow speculation regarding a possible role for WC1(+) gammadelta T-cells as a link between the innate and acquired immune systems which is instrumental in establishing an appropriate response.

Increased host resistance against Pneumocystis carinii pneumonia in gammadelta T-cell-deficient mice: protective role of gamma interferon and CD8(+) T cells

Although a clear relationship between alphabeta T-cell receptor-positive (alphabeta-TCR(+)) CD4(+) T cells and susceptibility to Pneumocystis carinii infection exists, the role of other T-cell subsets is less clearly defined. Previous studies have shown that gammadelta-TCR(+) T cells infiltrate into the lung during P. carinii pneumonia. Therefore, the present study examined the role of gammadelta-TCR(+) T cells in host defense against P. carinii pneumonia. C57BL/6 (control) and B6.129P2-Tcrd(tm1Mom) (gammadelta-TCR(+) T-cell-deficient) mice were inoculated intratracheally with P. carinii. At specific time points, mice were sacrificed and analyzed for P. carinii burden, T-cell subsets, and cytokine levels in lung tissue. Analysis of P. carinii burden showed a more rapid and complete resolution of infection in gammadelta-TCR(+) T-cell-deficient mice than in C57BL/6 controls. This augmented resolution was associated with elevated gamma interferon (IFN-gamma) levels in bronchoalveolar lavage fluid predominantly produced by CD8(+) T cells, as well as an increased recruitment of CD8(+) T cells in general. In separate experiments, neutralization of IFN-gamma or depletion of CD8(+) T cells early during infection abolished the augmented resolution previously observed in gammadelta-TCR(+) T-cell-deficient mice. These results show that the presence of gammadelta-TCR(+) T cells modulates host susceptibility to P. carinii pneumonia through interactions with pulmonary CD8(+) T cells and tissue production of IFN-gamma.

Extensive and preferential Fas/Fas ligand-dependent death of gammadelta T cells following infection with Listeria monocytogenes

In the spleens of mice infected intraperitoneally with the bacterium Listeria monocytogenes, both alphabeta and gammadelta T cells became rapidly activated, followed by a massive apoptotic death response predominantly within the gammadelta population. The death response involved two major splenic gammadelta T-cell subsets and was Fas/Fas ligand (Fas-L)-dependent. Among T cells isolated from the Listeria-infected spleen, Fas-L was almost exclusively expressed in gammadelta T cells. gammadelta T cells coexpressed Fas and Fas-L, suggesting activation-induced suicide as a mechanism of their death. In vivo treatment with an antibody specific for CD3epsilon induced activation, preferential Fas-L expression and apoptosis of gammadelta T cells, resembling the response pattern in listeriosis, whereas antibodies specific for T-cell receptor-beta (TCR-beta) or TCR-delta did not, suggesting that the complete response seen in listeriosis requires both gammadelta TCR engagement and additional stimuli. L. monocytogenes causes early nonspecific, Fas-independent lymphocyte death in heavily infected tissues. In contrast, the death response described here is selective, Fas-dependent and triggered at low local levels of bacteria, suggesting that it is controlled by interactions with other infection-activated host cells, and perhaps part of a regulatory circuit specifically curtailing gammadelta T cells.

Mechanisms of immune privilege for tumor cells by regulatory cytokines produced by innate and acquired immune cells

In murine tumors, innate immunity act as a trigger for the development of acquired immunity. The innate immune cells, natural killer (NK) and natural T (NKT) cells, generate the acquired immune cells, cytotoxic T lymphocytes (CTLs) and T helper (Th) 1 cells, by releasing interferon (IFN)-gamma. Regulatory T cells co-infiltrate with these tumoricidal effectors. In the innate phase, T cell receptor (TCR) gammadelta-bearing T (gammadelta T) and TCRalphabeta intermediate T cells are the regulators that suppress NK and NKT cells by elaborating interleukin (IL)-4, IL-10 and transforming growth factor (TGF)-beta. The acquired phase has Th3/T regulatory 1-like cells that inhibit CTLs and Th1 cells by TGF-beta. Thus, cytokines from regulatory T cells exert profound effects on tumor growth.

GammadeltaT cells regulate the development of hapten-specific CD8+ effector T cells in contact hypersensitivity responses

It has been reported that gammadeltaT cells are required for transfer of contact hypersensitivity responses by hapten-primed T cells. The mechanism by which they do so, however, remains to be elucidated. To specifically investigate the role of gammadeltaT cells in the development of contact hypersensitivity, this study employed Tdelta gene knockout mice that are deficient in gammadeltaT cells but are normal in the development of alphabetaT cells. The result indicates that contact hypersensitivity responses were significantly greater in gammadeltaT cell deficient mice than in wild-type mice. Similar results were obtained when wild-type mice were depleted of gammadeltaT cells with antibody treatment before hapten sensitization. Depletion of CD4+ T cells did not affect the increased contact hypersensitivity response in gammadeltaT cell deficient mice, suggesting that the effect of gammadeltaT cells is on CD8+ T cells and does not require CD4+ T cells. Further experiments demonstrated that primed CD8+ T cells from the deficient mice exhibited significantly higher CTL activity. The cytokine profile of CD4+ T cells was not significantly altered. Transfer of primed lymph node cells from hapten-primed gammadeltaT cell deficient mice elicited a similar level of contact hypersensitivity in naive wild-type and the deficient recipient mice, indicating that gammadeltaT cells have little effect on the elicitation of primed T cells and contact hypersensitivity responses. We conclude that gammadeltaT cells downregulate contact hypersensitivity responses to hapten sensitization by limiting the development of hapten-specific CD8+ effector T cells during sensitization and that this effect is independent of CD4+ T cells.

gamma/delta T cells in multiple sclerosis: chemokine and chemokine receptor expression

gamma/delta T cells are enriched in multiple sclerosis (MS) brain lesions and have been postulated to contribute to the pathogenesis of the disease. Increased expression of the chemokine receptors CCR5 and CXCR3 on T cells and raised amounts of the chemokines RANTES and IP-10 have been noted in the CSF and brain tissue of MS patients, but the contribution of gamma delta T cells to these increases is unknown. We therefore compared intracellular RANTES and IP-10 production as well as CCR5, CXCR3, and CXCR1 expression by gamma delta T cells derived from the blood and CSF of patients with MS and healthy controls (HC). We observed higher RANTES production by MS gamma delta than by alpha beta T cell lines. Most of the MS as well as the HC gamma delta and alpha beta T cell lines expressed CXCR3, while expression of CXCR1 was low. Interestingly, MS gamma delta T cell lines, compared to lines from HC, expressed lower levels of CCR5. Furthermore, CSF-derived gamma delta T cells had even lower CCR5 expression than blood-derived ones. The higher RANTES production by MS gamma delta T cell lines, together with a lower expression of CCR5, may reflect an autoregulatory loop, caused by an increased production of its ligands (RANTES, MIP-1 alpha, and MIP-1 beta) or due to other pro-inflammatory cytokines. Alternatively, we show that lower CCR5 expression could also reflect the result of repeated in vivo stimulation of gamma delta T cells by autoantigens.

Regulation of T cell-dependent autoantibody production by a gammadelta T cell line derived from lupus-prone mice

Lupus-prone (MRLxC57BL/6) F(1) mice lacking gammadelta T cells show more severe lupus than their T cell-intact counterparts, suggesting that gammadelta T cells down-modulate murine lupus. To determine the mechanisms for this effect, we assessed the capacity of gammadelta T cell lines derived from spleens of alphabeta T cell-deficient MRL/Mp-Fas(lpr) (MRL/Fas(lpr)) mice to down-regulate anti-dsDNA production generated by CD4(+)alphabeta T helper cell lines and activated B cells from wild-type MRL/Fas(lpr) mice. One line, GD12 (gd TCR(+), CD4(-)CD8(-)), had the capacity to reduce anti-dsDNA production in a contact-dependent manner. GD12 also killed activated MRL/Fas(lpr) (H-2(k)) B cells, with less cytolysis of resting B cells than that generated by in comparison to cytokine-matched gammadelta T cell lines. In addition, GD12 also killed activated B cells derived from C57BL/6-Fas(lpr) (H-2(b)) or beta(2)-microglobulin (beta(2) M)-deficient MRL/Fas(lpr) mice, suggesting cytolysis was neither MHC- nor CD1-restricted. Killing by GD12 was inhibited by anti-TNFalpha and anti-TNF-R1, and partially blocked by anti-gd TCR Fab fragments, but not by anti-FasL, anti-TNF-R2 (p75) or concanamycin A. IL-10 produced by GD12 also partially inhibited alphabeta Th1-dependent but not alphabeta Th2-dependent autoantibody production. These findings prove that we have identtified a gammadelta T cell line that suppresses autoantibody synthesis by alphabeta T-B cell collaboration in vitro.

Exaggerated proinflammatory and Th1 responses in the absence of gamma/delta T cells after infection with Listeria monocytogenes

While gamma/delta T cells are involved in host defense and immunopathology in a variety of infectious diseases, their precise role is not yet clearly defined. In the absence of gamma/delta T cells, mice die after infection with a dose of Listeria monocytogenes that is not lethal in immunologically intact animals. Morbidity might result from insufficient levels of cytokines normally produced by gamma/delta T cells or conversely from an excess of cytokines due to a lack of down-regulation of the inflammatory response in the absence of gamma/delta T cells. Consistent with a regulatory role, we found that systemic levels of proinflammatory cytokines (interleukin-6 [IL-6], IL-12, and gamma interferon [IFN-gamma]) were significantly higher in the absence of gamma/delta T cells during the innate phase of the response. Using combinations of genetically altered and immunodepleted mice, we found evidence for gamma/delta T-cell-mediated regulation of IFN-gamma production by multiple cell types of both lymphoid and myeloid lineages. The antigen-specific alpha/beta T-cell response that followed the exaggerated innate response was also increased in gamma/delta T-cell-deficient mice. These findings are consistent with an emerging picture from a variety of immune response models of a critical role for gamma/delta T cells in down-modulation of the immune response.

Both B and gammadelta TCR(+) lymphocytes regulate alphabeta TCR(+) lymphocytes involved in superantigen specific responses

Endogenous superantigens (SAg) presented by MHC class II IA molecules induce slow-evolving negative selection of alpha beta T cells. The role of both B and gamma delta T cells on the regulation of these SAg-specific alpha beta T cell responses was addressed in IA(b+)IE(b-) C57BL/6 mice bearing genetically induced B cell and gamma delta T cell deficiencies. B lymphocytes were required in the negative selection of Vbeta5(+)/Vbeta12(+) CD4(+) T cells. In contrast, gamma delta T cells positively stimulated the utilization of the same SAg-responsive alpha beta T cell subsets. These differences started in mature CD4(+) thymocytes and extended to naive T cell pools for B cell negative selection, and up to memory T cells for gamma deltaT cell influences. The levels of SAg-responsive T cells did not vary between C57BL/6 and double deficient (B cell and gamma delta T cell-deficient) congenic mice, implying that both B and gamma delta T cells acted through independent mechanisms.

A critical role for interleukin 18 in primary and memory effector responses to Listeria monocytogenes that extends beyond its effects on Interferon gamma production

The stimulation of interferon (IFN)-gamma by interleukin (IL)-12 has been shown to provide protection from intracellular pathogens such as Listeria monocytogenes. Tumor necrosis factor (TNF) is also a major player in the resolution of Listeria infections and is suggested to have more global effects than can be explained by the induction of IFN-gamma alone. Since IL-18 synergizes with IL-12 to induce IFN-gamma production by natural killer and T helper (Th)1 cells, we determined its role in responses to Listeria. IL-18 appeared to be even more potent than either IL-12 or IFN-gamma for protection against this pathogen and IL-18 enhanced bacterial clearance in the complete absence of IFN-gamma. Indeed IL-18 was comparable to TNF in its ability to resolve the infection and showed a lowered protective capacity in the absence of TNF. Moreover, IL-18 induced macrophages to secrete both TNF and nitric oxide after a Listeria infection. IL-18 was also essential for optimal IFN-gamma production by antigen-specific T cells. Therefore, IL-18 operates via its effects on both the innate immune response, including macrophages, as well as on Th1 cells, to protect against Listeria.

Antigen recognition and immunomodulation by gamma delta T cells in bovine tuberculosis

This report describes the in vitro proliferative responses of peripheral blood gammadelta T cells to defined mycobacterial protein Ags and the immunomodulatory effect of gammadelta T cells in cattle infected with Mycobacterium bovis. gammadelta T cell responses were specific to M. bovis infection because they were detected in cattle either experimentally or naturally infected with M. bovis, but were not present in uninfected controls. Proliferating gammadelta T cell cultures produced enhanced levels of IFN-gamma and TGF-beta, but not IL-2 in response to the more immunodominant mycobacterial AGS: Depletion of gammadelta T cells from PBMC resulted in an increased Ag-specific proliferation in half the animals tested, indicating a suppressive effect of gammadelta T cells upon other (alphabeta) T cell responses. Because gammadelta T cells constitute a major T cell population in the peripheral blood of cattle, the activities of gammadelta T cells described in this report could make a significant contribution to the immune response in bovine tuberculosis.

Gamma delta T cells are needed for ocular immune privilege and corneal graft survival

It has been recognized for over a century that the anterior chamber of the eye is endowed with a remarkable immune privilege. One contributing component is the Ag-specific down-regulation of systemic delayed-type hypersensitivity (DTH) that is induced when Ags are introduced into the anterior chamber. This phenomenon, termed anterior chamber-associated immune deviation (ACAID), culminates in the generation of regulatory cells that inhibit the induction (afferent suppression) and expression (efferent suppression) of DTH. Since gamma delta T cells play a major role in other forms of immune regulation, we suspected they might contribute to the induction and expression of ACAID. Mice treated with anti-gamma delta Ab failed to develop ACAID following anterior chamber injection of either soluble Ag (OVA) or alloantigens (spleen cells). Additional experiments with knockout mice confirmed that mice lacking functional gamma delta T cells also fail to develop ACAID. Using a local adoptive transfer of DTH assay, we found that gamma delta T cells were required for the generation of regulatory T cells, but did not function as the efferent regulatory cells of ACAID. The importance of gamma delta T cells in corneal allograft survival was confirmed by blocking gamma delta T cells with GL3 Ab before corneal transplantation. While in vivo treatment with normal hamster serum had no effect on corneal graft survival, infusion of anti-gamma delta Ab resulted in a profound increase in corneal allograft rejection. Thus, gamma delta T cells are needed for sustaining at least one aspect of ocular immune privilege and for promoting corneal allograft survival.

Lymphocyte subpopulations in the caecum mucosa of rats after infections with Eimeria separata: early responses in naive and immune animals to primary and challenge infections

This study aimed to characterise the local (intestinal) immune response of rats after primary and challenge infections with Eimeria separata. Naive rats and rats which had been immunised by two moderate infections were exposed to a heavy infection with 100000 oocysts per animal. Necropsies were performed 0, 24 and 48 h after infection and lymphocyte subpopulations were microscopically quantified in the caecum mucosa after marking by immunohistological techniques. There was no difference between naive and immune rats concerning the number of CD45R(+) (B) cells, whereas significantly more CD3(+) (T) cells were found in the caecum wall of the immune rats. CD4(+) T cells predominated in animals after primary infection, whereas CD8(+) T cells represented the major T-cell subset in challenged rats. The proportion of TCRgammadelta(+) T cells did not differ in the mucosa between the groups examined, whereas challenged rats showed significantly increased numbers of TCRalphabeta(+) T cells in the caecum wall when compared with animals after a primary infection. Thus, CD4(+) T cells may be particularly involved in the immune response to a primary infection of rats with E. separata whereas immunity to a challenge infection seems to be mediated predominantly by CD8(+) and TCRalphabeta(+) T cells.

Adoptively transferred gamma delta T cells indirectly regulate murine graft-versus-host reactivity following donor leukocyte infusion therapy in mice

The purpose of this study was to determine whether gamma delta T cells were able to regulate graft-vs-host (GVH) reactivity mediated by alpha beta T cells in murine recipients transplanted with MHC-mismatched marrow grafts. Studies were conducted using ex vivo-activated gamma delta T cells because this was a more clinically relevant strategy, and these cells have been shown to be capable of facilitating alloengraftment without causing GVH disease (GVHD). Coadministration of activated gamma delta T cells and naive alpha beta T cells at the time of bone marrow transplantation (BMT) significantly exacerbated GVHD when compared with naive alpha beta T cells alone. In contrast, when the administration of naive alpha beta T cells was delayed for 2 wk post-BMT, survival was significantly enhanced in mice transplanted with BM plus activated gamma delta T cells vs those given marrow cells alone. Mitigation of GVHD by activated gamma delta T cells occurred only at high doses (150 x 106) and was a unique property of gamma delta T cells, as activated alpha beta T cells were incapable of ameliorating the subsequent development of GVHD. Protection from GVHD was not due to the direct inhibition of naive alpha beta T cells by gamma delta T cells. Rather, gamma delta T cells mediated this effect indirectly through donor BM-derived alpha beta T cells that acted as the proximate regulatory population responsible for the decrease in GVH reactivity. Collectively, these data demonstrate that activated gamma delta T cells are capable of modulating the ability of MHC-incompatible nontolerant alpha beta T cells to cause GVHD after allogeneic BMT.

Characterization of the porcine gammadelta T-cell receptor structure and cellular distribution by monoclonal antibody PPT27

The T-cell receptor (TCR) is the critical structure involved in antigen recognition of T lymphocytes. Although the pig has a large proportion of circulating T lymphocytes bearing the gammadelta TCR, their study has been impeded due to the lack of specific antibodies. Here a monoclonal antibody (mAb) PPT27 directed to gammadelta TCR is described. Flow cytometry analyses showed that the mAb recognized a subset of T lymphocytes of which the majority expressed no CD2, CD4 and CD8 whilst the minority bore CD2 and CD8. The mAb precipitated a protein of 86 000 MW under non-reducing conditions and a doublet of 43 000 MW under reducing conditions from peripheral blood T lymphocytes lysed in nonidet P-40 buffer, whilst it precipitated the CD3-TCR complex from the cells lysed in digitonin. Further analysis revealed that the antibody recognized the majority, but not all, of the gammadelta T cells, suggesting that there may be more isotypes of gammadelta TCR than currently believed. The antibody was unable to stimulate gammadelta T cells to proliferate in vitro, suggesting that these cells are activated by a different activation mechanism from that of alphabeta T cells.

Identification of distinct lymphocyte subsets responding to subcellular fractions of Mycobacterium bovis bacille calmette-Guérin (BCG)

In order to investigate the ability of Mycobacterium bovis BCG vaccination to induce immune responses toward different classes of mycobacterial antigens and the cell populations involved in such responses, proliferation of distinct human lymphocyte subsets from BCG-vaccinated donors in response to different subcellular fractions of BCG was analysed and compared with that of not sensitized subjects. Proliferation of different cell subsets was evaluated by flow cytometric determination of bromodeoxyuridine incorporated into DNA of dividing cells and simultaneous identification of cell surface markers. Although a certain degree of variability was observed among different donors, after 6 days of in vitro stimulation BCG-vaccinated subjects displayed, as a mean, a stronger blastogenic response to all the classes of antigens compared with non-sensitized ones. PPD, culture filtrates and membrane antigens induced a predominant proliferation of CD4+ T cells. In contrast, preparations enriched in cytosolic antigens elicited strong proliferation of gammadelta+ T cells which, as a mean, represented 55% of the proliferating cells. Although to a lesser extent, proliferation of gammadelta+ T cells was also elicited by preparations enriched in membrane and cell wall antigens. In response to the latter preparation proliferation of CD4+ T cells and CD16+/CD3- (natural killer (NK)) cells was observed, as well. In particular, cell wall antigens were found to induce significantly higher levels of proliferation of NK cells compared with all the other classes of antigens.

A population of murine gammadelta T cells that recognize an inducible MHC class Ib molecule

Although gammadelta T cells are implicated in regulating immune responses, gammadelta T cell-ligand pairs that could mediate such regulatory functions have not been identified. Here, the expression of the major histocompatibility complex (MHC) class Ib T22 and the closely related T10 molecules is shown to be activation-induced, and they confer specificity to about 0.4% of the gammadelta T cells in normal mice. Thus, the increased expression of T22 and/or T10 might trigger immunoregulatory gammadelta T cells during immune responses. Furthermore, the fast on-rates and slow off-rates that characterize this receptor/ligand interaction would compensate for the low ligand stability and suggest a high threshold for gammadelta T cell activation.

Decreased severity of myelin oligodendrocyte glycoprotein peptide 33 - 35-induced experimental autoimmune encephalomyelitis in mice with a disrupted TCR delta chain gene

Immunization of C57BL / 6 mice with myelin oligodendrocyte glycoprotein (MOG) peptide (p) 35 - 55 induces chronic experimental autoimmune encephalomyelitis (EAE). The role of gamma delta T cells in the regulation of EAE is unclear. We investigated gamma delta T cells in C57BL / 6 wild-type mice and C57BL / mice with a disrupted TCRdelta chain gene (delta(- / -) mice) using MOG p35 - 55. We found significantly less disease in delta(- / -) mice immunized with MOG / complete Freund's adjuvant (mean maximal EAE score 4.3 +/- 0.8 in wild-type vs. 2.3 +/- 0.5 in delta(- / -) mice). Transfer of wild-type spleen cells restored the ability of delta(- / -) mice to develop equally severe EAE as wild-type mice. In addition to IFN-gamma, IL-2, IL-5 and IL-10 was decreased in delta(- / -) mice. Decreased immune responses were also seen in delta(- / -) animals immunized with OVA peptide or protein and in concanavalin A-stimulated splenocytes from delta(- / -) mice. Enriched dendritic cells from delta(- / -) mice secreted significantly less TNF-alpha in response to lipopolysaccharide stimulation. Furthermore, when EAE was induced by adoptive transfer of an anti-MOG p35 - 55 alpha beta T cell line, there was a striking reduction of disease incidence (0 %) and severity in delta(- / -) as compared to wild-type mice (83 % incidence). delta(- / -) mice showed no cellular infiltration in the spinal cord whereas wild-type animals had infiltration of macrophages, B cells, alpha beta- and gamma delta T cells. In adoptive transfer EAE, there was reduced IL-2 and IFN-gamma secretion in delta(- / -) mice. These results demonstrate an impaired immune response in the delta(- / -) mouse that is associated with a defect in developing both actively induced and adoptively transferred EAE.

gammadelta T cells regulate mucosally induced tolerance in a dose-dependent fashion

We used gammadelta TCR-deficient (TCRdelta(-/-)) mice to examine the role of gammadelta T cells for induction of mucosal responses and systemic tolerance to high versus low doses of oral antigen. When either TCRdelta(-/-) or TCRdelta(+/+) mice were immunized orally with a high dose of ovalbumin (OVA) prior to parenteral challenge, systemic IgG and IgE antibody responses were markedly reduced in both types of mice, while mucosal IgA responses were reduced only in the TCRdelta(-/-) mice. Reduced T cell proliferative responses and delayed-type hypersensitivity were seen in TCRdelta(-/-) and TCRdelta(+/+) mice given the high dose of OVA. Antigen-induced T(h)1 and T(h)2 cytokine production by splenic CD4(+) T cells was severely inhibited in orally tolerized TCRdelta(-/-) and TCRdelta(+/+) mice. In contrast, while oral tolerance associated with increased levels of IL-10 synthesis was induced by a low dose of OVA in TCRdelta(+/+) mice, the TCRdelta(-/-) mice were not tolerized and failed to produce IL-10. Our findings indicate that gammadelta T cells play a significant immunoregulatory role in IL-10-mediated, low-dose oral tolerance induction, but are not essential participants in the induction of systemic tolerance to orally introduced antigens given in larger doses.

Increased gammadelta T-cell populations in draining lymph nodes of lambs during the elicitation phase of dinitrochlorobenzene-induced contact hypersensitivity

Ten lambs were sensitised with the hapten DNCB in an acetone/olive oil vehicle. The hapten/vehicle solution was applied onto the skin on the shaved ventral surface of the right ear. Two weeks later these lambs were rechallenged with the DNCB/vehicle solution. Simultaneously, ten non-sensitised lambs were treated with vehicle only, serving as vehicle controls. The 20 lambs were slaughtered 48 h after challenge/vehicle treatment, along with ten untreated animals serving as normal controls. Specimens of draining lymph nodes were collected from the 30 animals. All lambs were between 149 and 187 days old. Lymph node cryosections were stained for several leukocyte markers using monoclonal antibodies with the ABC immunohistochemical method. The stained sections were subsequently assessed in three different cortical compartments in each section, using an image analysis system. The resulting measurements from the three groups were compared. A marked increase of gammadelta T cells was detected in the DNCB group. The number of CD4+ T helper cells was decreased in the DNCB group compared with the normal control group, but not with the vehicle control group. No differences were revealed for CD8+ T cytotoxic cells or B cells. These findings were interpreted to be the consequences of possible downregulatory mechanisms protecting the lymphoid tissue from hypersensitivity. The prominence of gammadelta T-cells could indicate that these cells are involved in downregulation.

The role of intrahepatic gammadelta-T cells for liver injury induced by Salmonella infection in mouse

Liver injury was induced after infection with Salmonella choleraesuis 31N-1. In T-cell receptor-delta knockout mice, serum alanine transferase level was significantly decreased in comparison with normal control mice after Salmonella infection. On the contrary, in vivo administration of anti-gammadelta T-cell receptor monoclonal antibody (UC7-13D5) to stimulate gammadelta-T cells in infected mice significantly increased serum alanine transferase level but decreased bacterial growth compared with infected mice given control antibody (UC8; hamster IgG). These data suggest that gammadelta-T cells have effector activities not only for protection but also for liver injury during Salmonella infection.

gamma delta T-cells may interfere with a productive immune response in Plasmodium yoelii infections

Mice lacking alpha beta T-cells or gamma delta T-cells were infected with Plasmodium yoelii 17X NL (non-lethal) and followed for parasitaemia and cytokine production. While the parasitaemia in wild type mice resolved after reaching a peak value of 30 to 50%, it persisted in the -alpha beta T-cell mice until death. However, in the -gamma delta T-cell mice the peak parasitaemia was 12.5% of the levels seen in the wild type and -alpha beta T-cell mice and resolved faster than in the wild type mice. Higher levels of IL-10 and IFN-gamma were consistently found in the wild type and -gamma delta T-cell mice but not in the -alpha beta T-cell mice.

Cross-talk between gammadelta T lymphocytes and immune cells in humoral response

The role of gamma delta T cells in immunoregulation is largely unknown. In the current study we noted that gamma delta T cells play a positive role in the humoral response. These positively acting gamma delta T cells are required for the successful adoptive cell transfer of the humoral response, as well as for in vitro generation of plaque-forming cells (PFC). The presented results show that gammadelta T cells cause an increase in interleukin-10 (IL-10) production, which partly elucidates the mechanism of action of these cells. However, experiments with cell culture inserts strongly suggest that direct cell-cell contact between immune and gamma delta H-2-compatible regulatory T cells is critical to the exertion of the positive immunoregulatory function of gamma delta cells. The mechanism of cross-talk between these two cell populations is still not clear but we regard as most likely that the positively acting gamma delta T cells may interact with a complex of heat-shock protein-non-polymorphic MHC (IB) on the surface of T helper type 2 and/or B cells. This could provide, by direct cell-cell contact, the cognate recognition between gamma delta T-cell receptors and heat-shock protein-MHC that leads to positive internal signalling in the immune cells.