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

Comparative gamma delta T cell immunology: a focus on mycobacterial disease in cattle

A theme among many pathogenic mycobacterial species affecting both humans and animals is a prolonged asymptomatic or latent period that can last years to decades. The mechanisms that favor progression to active disease are not well understood. Pathogen containment is often associated with an effective cell-mediated or T-helper 1 immune profile. With certain pathogenic mycobacteria, such as Mycobacterium avium subspecies paratuberculosis, a shift to active clinical disease is associated with loss of T-helper 1 immunity and development of an ineffective humoral or T-helper 2 immune response. Recently γδ T cells have been shown to play a role early in mycobacterial infections and have been hypothesized to influence disease outcome. The purpose of this paper is to compare recent advancements in our understanding of γδ T cells in humans, cattle, and mice and to discuss roles of γδ T cells in host response to mycobacterial infection.

γδT-cell function in sepsis is modulated by C5a receptor signalling

We previously showed that γδT cells are involved in the pathogenesis of sepsis, but, the underlying mechanisms remained unclear. The present study demonstrates, for the first time, that γδT cells express the complement C5a receptor (C5aR, CD88) and that CD88 expression in γδT cells was up-regulated in mice following sepsis both at protein and mRNA levels. Complement C5a itself contributed to the regulation of C5aR expression on γδT cells, as (i) neutralization of C5a in vivo prevented the expression of C5aR on γδT cells in septic mice and (ii) incubation of mouse spleen cells or purified γδT cells with recombinant C5a in vitro increased CD88 expression by γδT cells at both protein and mRNA levels. C5a receptor on γδT cells also mediates increased interleukin-17 (IL-17) expression as incubation of mouse spleen cells or purified γδT cells with recombinant C5a promotes the IL-17 expression by γδT cells. Ligation of the C5aR on γδT cells activated the phosphoinositide 3-kinase (PI3K)/Akt signalling pathway, which enhances CD88 expression and promotes IL-17 secretion. These results demonstrate that C5a acts directly on the C5aR expressed on γδT cells, resulting in cell activation, and subsequently enhances their capacity for IL-17 production. The up-regulation of the PI3K/Akt pathway following C5a stimulation contributes to up-regulation of γδT-cell function.

Bovine γδ T cells: cells with multiple functions and important roles in immunity

The γδ T-cell receptor (TCR)-positive lymphocytes are a major circulating lymphocyte population in cattle, especially in young calves. In contrast, human and mice have low levels of circulating γδ TCR(+) T cells (γδ T cells). The majority of the circulating γδ T cells in ruminants express the workshop cluster 1 (WC1) molecule and are of the phenotype WC1(+) CD2(-) CD4(-) CD8(-). WC1 is a 220000 molecular weight glycoprotein with homology to the scavenger receptor cysteine-rich (SRCR) family, closely related to CD163. The existence of 13 members in the bovine WC1 gene family has recently been demonstrated and although murine and human orthologues to WC1 genes exist, functional gene products have not been identified in species other than ruminants and pigs. Highly diverse TCRδ usage has been reported, with expanded variable genes in cattle compared to humans and mice. Differential γ chain usage is evident between populations of bovine γδ T cells, this may have implications for functionality. There is a growing body of evidence that WC1(+) γδ T cells are important in immune responses to mycobacteria and may have important roles in T cell regulation and antigen presentation. In this review, we will summarize recent observations in γδ T cell biology and the importance of γδ T cells in immune responses to mycobacterial infections in cattle.

Rapid and transient activation of γδ T cells to IFN-γ production, NK cell-like killing, and antigen processing during acute virus infection

γδ T cells are the majority peripheral blood T cells in young cattle. The role of γδ T cells in innate responses against infection with foot-and-mouth disease virus was analyzed on consecutive 5 d following infection. Before infection, bovine WC1(+) γδ T cells expressed a nonactivated phenotype relative to CD62L, CD45RO, and CD25 expression and did not produce IFN-γ ex vivo. Additionally, CD335 expression was lacking and no spontaneous target cell lysis could be detected in vitro, although perforin was detectable at a very low level. MHC class II and CD13 expression were also lacking. Following infection with foot-and-mouth disease virus, expression of CD62L and CD45RO was greatly reduced on WC1(+) γδ T cells, and unexpectedly, CD45RO expression did not recover. A transient increase in expression of CD25 correlated with production of IFN-γ. Expression of CD335 and production of perforin were detected on a subset of γδ T cells, and this correlated with an increased spontaneous killing of xenogeneic target cells. Furthermore, increased MHC class II expression was detected on WC1(+) γδ T cells, and these cells processed protein Ags. These activities are rapidly induced, within 3 d, and wane by 5 d following infection. All of these functions, NK-like killing, Ag processing, and IFN-γ production, have been demonstrated for these cells in various species. However, these results are unique in that all these functions are detected in the same samples of WC1(+) γδ T cells, suggesting a pivotal role of these cells in controlling virus infection.

Regulation by intestinal γδ T cells during establishment of food allergic sensitization in mice

BACKGROUND

Food allergy affects approximately 5% of children and is the leading cause of hospitalization for anaphylactic reactions in westernized countries. The mucosal adjuvant cholera toxin induces allergic sensitization to co-administered proteins in mice, while feeding the protein alone induces oral tolerance. Intestinal γδ T cells could be of importance in the induction of oral tolerance. This study aims to investigate whether γδ T cells have functional relevance in food allergic sensitization.

METHODS

Changes in γδ T cells on days 1, 2, 3, and 7 after initiation of food allergy were evaluated using flowcytometry. Furthermore, the anti-γδ T-cell receptor (TCR) antibody UC7 was used to block the γδ TCR in mice in vivo, followed by sensitization to peanut. After 4 weeks, peanut-specific antibodies in serum and cytokine production in spleen were measured.

RESULTS

Induction of food allergy resulted in a profound decrease in the percentage of γδ T cells in intestinal tissues and Peyer's Patches, but not in mesenteric lymph nodes or spleen. This decrease could be detected from days 1 to 2 after the initiation of food allergy and the number of γδ T cells returned to normal on day 7. Blockade of the γδ TCR resulted in elevated food allergic responses upon sensitization with peanut characterized by increased IgE and Th2 cytokine production in splenocytes.

CONCLUSION

These results demonstrate a unique regulatory role of γδ T cells, suggesting that targeting γδ T cells in the intestine may contribute to strategies to prevent and possibly treat food allergy.

Cytokine requirements for the differentiation and expansion of IL-17A- and IL-22-producing human Vgamma2Vdelta2 T cells

Human gammadelta T cells expressing the Vgamma2Vdelta2 TCR play important roles in immune responses to microbial pathogens by monitoring prenyl pyrophosphate isoprenoid metabolites. Most adult Vgamma2Vdelta2 cells are memory cytotoxic cells that produce IFN-gamma. Recently, murine gammadelta T cells were found to be major sources of IL-17A in antimicrobial and autoimmune responses. To determine if primate gammadelta T cells play similar roles, we characterized IL-17A and IL-22 production by Vgamma2Vdelta2 cells. IL-17A-producing memory Vgamma2Vdelta2 cells exist at low but significant frequencies in adult humans (1:2762 T cells) and at even higher frequencies in adult rhesus macaques. Higher levels of Vgamma2Vdelta2 cells produce IL-22 (1:1864 T cells), although few produce both IL-17A and IL-22. Unlike adult humans, in whom many IL-17A+ Vgamma2Vdelta2 cells also produce IFN-gamma (Tgammadelta1/17), the majority of adult macaques IL-17A+ Vdelta2 cells (Tgammadelta17) do not produce IFN-gamma. To define the cytokine requirements for Tgammadelta17 cells, we stimulated human neonatal Vgamma2Vdelta2 cells with the bacterial Ag, (E)-4-hydroxy-3-methyl-but-2-enyl pyrophosphate, and various cytokines and mAbs in vitro. We find that IL-6, IL-1beta, and TGF-beta are required to generate Tgammadelta17 cells in neonates, whereas Tgammadelta1/17 cells additionally required IL-23. In adults, memory Tgammadelta1/17 and Tgammadelta17 cells required IL-23, IL-1beta, and TGF-beta, but not IL-6. IL-22-producing cells showed similar requirements. Both neonatal and adult IL-17A+ Vgamma2Vdelta2 cells expressed elevated levels of retinoid-related orphan receptor gammat. Our data suggest that, like Th17 alphabeta T cells, Vgamma2Vdelta2 T cells can be polarized into Tgammadelta17 and Tgammadelta1/17 populations with distinct cytokine requirements for their initial polarization and later maintenance.

Gammadelta T cell effector functions: a blend of innate programming and acquired plasticity

Gammadelta T cells have several innate cell-like features that allow their early activation following recognition of conserved stress-induced ligands. Here we review recent observations revealing the ability of gammadelta T cells to rapidly produce cytokines that regulate pathogen clearance, inflammation and tissue homeostasis in response to tissue stress. These studies provide insights into how they acquire these properties, through both developmental programming in the thymus and functional polarization in the periphery. Innate features of gammadelta T cells underlie their non-redundant role in several physiopathological contexts and are therefore being exploited in the design of new immunotherapeutic approaches.

gammadelta T cell subsets: a link between TCR and function?

The gammadelta T lmphocytes are often divided into subsets based upon expression of certain TCR components. This division was initially made because gammadelta T cells residing in particular epithelia were found to show tissue specific differences in their TCRs. Many examples now show that gammadelta T cell subsets also appear to be biased to carry out particular functions. This suggests that particular gammadelta TCR types direct the cells to acquire a certain type of functional programming during thymic development. Here, we describe functionally distinct, TCR-defined gammadelta T cell subsets, and evidence that their functions are predetermined in the thymus.

Prolonged antigen survival and cytosolic export in cross-presenting human gammadelta T cells

Human blood Vgamma9Vdelta2 T cells respond to signals from microbes and tumors and subsequently differentiate into professional antigen-presenting cells (gammadelta T-APCs) for induction of CD4(+) and CD8(+) T cell responses. gammadelta T-APCs readily take up and degrade exogenous soluble protein for peptide loading on MHC I, in a process termed antigen cross-presentation. The mechanisms underlying antigen cross-presentation are ill-defined, most notably in human dendritic cells (DCs), and no study has addressed this process in gammadelta T-APCs. Here we show that intracellular protein degradation and endosomal acidification were significantly delayed in gammadelta T-APCs compared with human monocyte-derived DCs (moDCs). Such conditions are known to favor antigen cross-presentation. In both gammadelta T-APCs and moDCs, internalized antigen was transported across insulin-regulated aminopeptidase (IRAP)-positive early and late endosomes; however, and in contrast to various human DC subsets, gammadelta T-APCs efficiently translocated soluble antigen into the cytosol for processing via the cytosolic proteasome-dependent cross-presentation pathway. Of note, gammadelta T-APCs cross-presented influenza antigen derived from virus-infected cells and from free virus particles. The robust cross-presentation capability appears to be a hallmark of gammadelta T-APCs and underscores their potential application in cellular immunotherapy.

Analysis of gamma delta T cell functions in the mouse

Mouse models of disease and injury have been invaluable in investigations of the functional role of gammadelta T cells. They show that gammadelta T cells engage in immune responses both early and late, that they can function both polyclonally and as peripherally selected clones, and that they can be effector cells and immune regulators. They also suggest that functional development of gammadelta T cells occurs stepwise in thymus and periphery, and that it is governed by gammadelta TCR-signaling and other signals. Finally, they indicate that gammadelta T cell functions often segregate with TCR-defined subsets, in contrast to conventional T cells. From the functional studies in mice and other animal models, gammadelta T cells emerge as a distinct lymphocyte population with a unique and broad functional repertoire, and with important roles in Ab responses, inflammation and tissue repair. They also are revealed as a potentially useful target for immune intervention.

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.

Cell-mediated immunity evaluation in foals infected with virulent equine herpesvirus-1 by multi-parameter flow cytometry

The cell-mediated immune (CMI) response of foals to virulent equine herpesvirus-1 (EHV-1) infection was evaluated by multi-parameter flow cytometry (FCM). Ten 7-8-month-old EHV-1 seronegative foals were infected intranasally with virulent EHV-1 and 10 foals served as uninfected controls. Blood samples were collected 6 and 7 weeks after infection to test for specific CMI responses to live heterologous EHV-1 recall antigen. The activation markers included major histocompatibility complex class II (MHC II), intracellular interferon gamma (IFN-gamma) and interleukin 4 (IL-4). The results from both tests were averaged before statistical analysis. Following EHV-1 stimulation, the MHC II expression index (EI) increased significantly in CD2+CD4+CD8- and CD2+CD4-CD8+ subsets of the infected group. At 4 days after incubation, the non-antigen stimulated CD2+CD4-CD8- subset of the infected group expressed a high percentage (61.1%) of MHC II. When stimulated with EHV-1, the MHC II expression declined significantly but remained at a relatively high percentage (34.4%). The IFN-gamma EI was significantly higher in infected foals in all major T cell subsets (CD2+) while only the CD2+CD4+CD8- subset showed a significant increase in intracellular IL-4 EI. The FCM results showed strong specific CMI responses to EHV-1 by all three tested parameters compared to the control group (p<0.01). The high MHC II expression in the CD2+CD4-CD8- subset suggests that this T cell subset may represent a gammadelta TCR repertoire and thereby plays an important role as antigen presenting cells in the horse, as reported in other species. Being able to simultaneously quantify the frequency of specific lymphocyte subsets and the expression of cytokines that characterize activation of lymphocytes and protective CMI by multi-parameter FCM enables evaluation of subset-specific CMI responses to EHV-1 infection. This system can be applied to measure CMI responses to other equine vaccines and pathogens.

Human gamma delta T cells: a lymphoid lineage cell capable of professional phagocytosis

Professional phagocytosis in mammals is considered to be performed exclusively by myeloid cell types. In this study, we demonstrate, for the first time, that a mammalian lymphocyte subset can operate as a professional phagocyte. By using confocal microscopy, transmission electron microscopy, and functional Ag presentation assays, we find that freshly isolated human peripheral blood gammadelta T cells can phagocytose Escherichia coli and 1 microm synthetic beads via Ab opsonization and CD16 (FcgammaRIII), leading to Ag processing and presentation on MHC class II. In contrast, other CD16(+) lymphocytes, i.e., CD16(+)/CD56(+) NK cells, were not capable of such functions. These findings of distinct myeloid characteristics in gammadelta T cells strongly support the suggestion that gammadelta T cells are evolutionarily ancient lymphocytes and have implications for our understanding of their role in transitional immunity and the control of infectious diseases and cancer.

Chronic inflammation and asthma

Allergic asthma is a complex and chronic inflammatory disorder which is associated with airway hyper-responsiveness and tissue remodelling of the airway structure. Although originally thought to be a Th2-driven inflammatory response to inhaled innocuous allergen, the immune response in asthma is now considered highly heterogeneous. There are now various in vivo systems which have been designed to examine the pathways leading to the development of this chronic immune response and reflect, in part this heterogeneity. Furthermore, the emergence of endogenous immunoregulatory pathways and active pro-resolving mediators hold great potential for future therapeutic intervention. In this review, the key cellular and molecular mediators relating to chronic allergic airway disease are discussed, as well as emerging players in the regulation of chronic allergic inflammation.

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.

Interleukin-17-producing gammadelta+ T cells protect NOD mice from type 1 diabetes through a mechanism involving transforming growth factor-beta

Whether interleukin (IL)-17 promotes a diabetogenic response remains unclear. Here we examined the effects of neutralization of IL-17 on the progress of adoptively transferred diabetes. IL-17-producing cells in non-obese diabetic (NOD) mice were identified and their role in the pathogenesis of diabetes examined using transfer and co-transfer assays. Unexpectedly, we found that in vivo neutralization of IL-17 did not protect NOD-severe combined immunodeficiency (SCID) mice against diabetes transferred by diabetic splenocytes. In NOD mice, gammadelta(+) T cells were dominated by IL-17-producing cells and were found to be the major source of IL-17. Interestingly, these IL-17-producing gammadelta T cells did not exacerbate diabetes in an adoptive transfer model, but had a regulatory effect, protecting NOD mice from diabetes by up-regulating transforming growth factor (TGF)-beta production. Our data suggest that the presence of IL-17 did not increase the chance of the development of diabetes; gammadelta T cells protected NOD mice from diabetes in a TGF-beta-dependent manner, irrespective of their role as major IL-17 producers.

Gammadelta T cells in EAE: early trafficking events and cytokine requirements

We have previously shown that gammadelta T cells traffic to the CNS during EAE with concurrently increased expression of beta(2)-integrins and production of IFN-gamma and TNF-alpha. To extend these studies, we transferred bioluminescent gammadelta T cells to WT mice and followed their movement through the acute stages of disease. We found that gammadelta T cells rapidly migrated to the site of myelin oligodendrocyte glycoprotein peptide injection and underwent massive expansion. Within 6 days after EAE induction, bioluminescent gammadelta T cells were found in the spinal cord and brain, peaking in number between days 10 and 12 and then rapidly declining by day 15. Reconstitution of gammadelta T cell(-/-) mice with gammadelta T cells derived from beta(2)-integrin-deficient mice (CD11a, -b or -c) demonstrated that gammadelta T-cell trafficking to the CNS during EAE is independent of this family of adhesion molecules. We also examined the role of gammadelta T-cell-produced IFN-gamma and TNF-alpha in EAE and found that production of both cytokines by gammadelta T cells was required for full development of EAE. These results indicate that gammadelta T cells are critical for the development of EAE and suggest a therapeutic target in demyelinating disease.

Cross-presenting human gammadelta T cells induce robust CD8+ alphabeta T cell responses

Gammadelta T cells are implicated in host defense against microbes and tumors but their mode of function remains largely unresolved. Here, we have investigated the ability of activated human Vgamma9Vdelta2(+) T cells (termed gammadelta T-APCs) to cross-present microbial and tumor antigens to CD8(+) alphabeta T cells. Although this process is thought to be mediated best by DCs, adoptive transfer of ex vivo antigen-loaded, human DCs during immunotherapy of cancer patients has shown limited success. We report that gammadelta T-APCs take up and process soluble proteins and induce proliferation, target cell killing and cytokine production responses in antigen-experienced and naïve CD8(+) alphabeta T cells. Induction of APC functions in Vgamma9Vdelta2(+) T cells was accompanied by the up-regulation of costimulatory and MHC class I molecules. In contrast, the functional predominance of the immunoproteasome was a characteristic of gammadelta T cells irrespective of their state of activation. Gammadelta T-APCs were more efficient in antigen cross-presentation than monocyte-derived DCs, which is in contrast to the strong induction of CD4(+) alphabeta T cell responses by both types of APCs. Our study reveals unexpected properties of human gammadelta T-APCs in the induction of CD8(+) alphabeta T effector cells, and justifies their further exploration in immunotherapy research.

Role of γδ T Cells in Lung Inflammation

The resident population of γδ T cells in the normal lung is small but during lung inflammation, γδ T cells can increase dramatically. Histological analysis reveals diverse interactions between γδ T cells and other pulmonary leukocytes. Studies in animal models show that γδ T cells play a role in allergic lung inflammation where they can protect normal lung function, that they also are capable of resolving infection-induced pulmonary inflammation, and that they can help preventing pulmonary fibrosis. Lung inflammation threatens vital lung functions. Protection of the lung tissues and their functions during inflammation is the net-effect of opposing influences of specialized subsets of γδ T cells as well as interactions of these cells with other pulmonary leukocytes.