Different Potentials of γδ T Cell Subsets in Regulating Airway Responsiveness: Vγ1+ Cells, but Not Vγ4+ Cells, Promote Airway Hyperreactivity, Th2 Cytokines, and Airway Inflammation

γδ T Lymphocytes Coordinate Eosinophil Influx during Allergic Responses

Tissue eosinophil infiltration, which is a hallmark of allergic and helminthic diseases, is mainly coordinated by T lymphocytes, via the production of eosinophilotactic chemokines. Among T lymphocyte subsets, lymphocytes expressing γδ T cell receptor have been determined as a key factor for eosinophil accumulation via direct and indirect mechanisms. This knowledge is strongly supported by the fact that, in different experimental models of eosinophilic airway inflammation and helminth-induced Th2 lung inflammation, an evident tissue accumulation of γδ T lymphocytes is observed. In addition, the depletion of γδ T lymphocytes is correlated with the impairment of eosinophil accumulation in inflamed tissue. γδ T lymphocytes are non-conventional T lymphocytes, which comprise a minor T lymphocyte subset, mainly distributed in the tissue, and present crucial roles in innate and acquired immune responses. γδ T lymphocytes recognize several danger- and pathogen-associated molecular pattern molecules and stress antigens in a MHC-independent fashion and can provide rapid tissue-specific responses, via the production of a wide range of chemical mediators capable to modulate other cell populations. These mediators include chemoattractant cytokines and chemokines that attract eosinophils into the tissue by either direct recognition (such as IL-5, CCL11/eotaxin), or indirect mechanisms via the modulation of αβ T lymphocytes and macrophages (through the production of interferon-γ, IL-4, and CCL2/Monocyte chemoattractant protein-1, MCP-1, for example). The present review presents an overview of how γδ T lymphocytes coordinate eosinophil accumulation in allergy, by focusing on their role in airway inflammation and by discussing the involvement of cytokines and chemokines in this phenomenon.

Immunomodulation at epithelial sites by obesity and metabolic disease

Obesity and related type 2 diabetes are increasing at epidemic proportions globally. It is now recognized that inflammatory responses mediated within the adipose tissue in obesity are central to the development of disease. Once initiated, chronic inflammation associated with obesity leads to the modulation of immune cell function. This review will focus specifically on the impact of obesity on γδ T cells, a T-cell subset that is found in high concentrations in epithelial tissues such as the skin, intestine, and lung. Epithelial γδ T cell function is of particular concern in obesity as they are the guardians of the epithelial barrier and mediate repair. A breakdown in their function, and subsequently the deterioration of the epithelium can result in dire consequences for the host. Obese patients are more prone to non-healing injuries, infection, and disease. The resulting inflammation from these pathologies further perpetuates the disease condition already present in obese hosts. Here we will provide insight into the immunomodulation of γδ T cells that occurs in the epithelial barrier during obesity and discuss current therapeutic options.

Vγ4+ T cells regulate host immune response to West Nile virus infection

The Vγ4(+) cells, a subpopulation of peripheral γδ T cells, are involved in West Nile virus (WNV) pathogenesis, but the underlying mechanism remains unclear. In this study, we found that WNV-infected Vγ4(+) cell-depleted mice had lower viremia and a reduced inflammatory response in the brain. The Vγ4(+) cells produced IL-17 during WNV infection, but blocking IL-17 signaling did not affect host susceptibility to WNV encephalitis. We also noted that there was an enhanced magnitude of protective splenic Vγ1(+) cell expansion in Vγ4(+) cell-depleted mice compared to that in controls during WNV infection. In addition, Vγ4(+) cells of WNV-infected mice had a higher potential for producing TGF-β. The γδ T cells of WNV-infected Vγ4(+) cell-depleted mice had a higher proliferation rate than those of WNV-infected controls upon ex vivo stimulation with anti-CD3, and this difference was diminished in the presence of TGF-β inhibitor. Finally, Vγ4(+) cells of infected mice contributed directly and indirectly to the higher level of IL-10, which is known to play a negative role in immunity against WNV infection. In summary, Vγ4(+) cells suppress Vγ1(+) cell expansion via TGF-β and increase IL-10 level during WNV infection, which together may lead to higher viremia and enhanced brain inflammation.

Characterization of immune modulating functions of γδ T cell subsets in a gnotobiotic pig model of human rotavirus infection

We characterized immune modulating functions of porcine γδ T cell subsets in rotavirus infection using a gnotobiotic pig model of human rotavirus infection and sort-purified lymphocyte autologous co-cultures. We demonstrated that CD2+CD8- and CD2-CD8- γδ T cells have mainly pro-inflammatory function as evident by directly secreting IFN-γ or promoting CD4+ αβ T cell proliferation and IFN-γ production, whereas CD2+CD8+ γδ T cells mainly exert regulatory T cell function by expressing FoxP3, secreting IL-10 and TGF-β or increasing IL-10 and TGF-β production by CD4+ αβ T cells. γδ T cells responded to rotavirus infection by increasing TLR2, TLR3, TLR9 expression and IFN-γ and/or TGF-β production. The CD8- subsets likely differentiate into CD8+ subset by acquiring CD8 expression, explaining in part the apparently dual functions of CD2+CD8+ and CD2+CD8- subsets. Thus, both CD8+ and CD8- γδ T cell subsets can contribute to anti-rotavirus immunity and to the maintenance and restoration of intestinal and systemic homeostasis.

Vγ4 γδ T cell-derived IL-17A negatively regulates NKT cell function in Con A-induced fulminant hepatitis

Con A-induced fulminant hepatitis is a well-known animal model for acute liver failure. However, the role of γδ T cells in this model is undefined. In this report, using TCR δ(-/-) mice, we demonstrated a protective role of γδ T cells in Con A-induced hepatitis model. TCR δ(-/-) mice showed significantly decreased levels of IL-17A and IL-17F in the Con A-treated liver tissue, and reconstitution of TCR δ(-/-) mice with wild-type (Wt), but not IL-17A(-/-), γδ T cells significantly reduced hepatitis, strongly suggesting a critical role of IL-17A in mediating the protective effect of γδ T cells. Interestingly, only Vγ4, but not Vγ1, γδ T cells exerted such a protective effect. Furthermore, depletion of NKT cells in TCR δ(-/-) mice completely abolished hepatitis, and NKT cells from Con A-challenged liver tissues of TCR δ(-/-) mice expressed significantly higher amounts of proinflammatory cytokine IFN-γ than those from Wt mice, indicating that γδ T cells protected hepatitis through targeting NKT cells. Finally, abnormal capacity of IFN-γ production by NKT cells of TCR δ(-/-) mice could only be downregulated by transferring Wt, but not IL-17(-/-), Vγ4 γδ T cells, confirming an essential role of Vγ4-derived IL-17A in regulating the function of NKT cells. In summary, our report thus demonstrated a novel function of Vγ4 γδ T cells in mediating a protective effect against Con A-induced fulminant hepatitis through negatively regulating function of NKT cells in an IL-17A-dependent manner, and transferring Vγ4 γδ T cells may provide a novel therapeutic approach for this devastating liver disease.

Regulatory role of Vγ1 γδ T cells in tumor immunity through IL-4 production

It has been demonstrated that the two main subsets of peripheral γδ T cells, Vγ1 and Vγ4, have divergent functions in many diseases models. Recently, we reported that Vγ4 γδ T cells played a protective role in tumor immunity through eomesodermin-controlled mechanisms. However, the precise roles of Vγ1 γδ T cells in tumor immunity, especially whether Vγ1 γδ T cells have any interaction with Vγ4 γδ T cells, remain unknown. We demonstrated in this paper that Vγ1 γδ T cells suppressed Vγ4 γδ T cell-mediated antitumor function both in vitro and in vivo, and this suppression was cell contact independent. Using neutralizing anti-IL-4 Ab or IL-4(-/-) mice, we determined the suppressive factor derived from Vγ1 γδ T cells was IL-4. Indeed, treatment of Vγ4 γδ T cells with rIL-4 significantly reduced expression levels of NKG2D, perforin, and IFN-γ. Finally, Vγ1 γδ T cells produced more IL-4 and expressed significantly higher level of GATA-3 upon Th2 priming in comparison with Vγ4 γδ T cells. Therefore, to our knowledge, our results established for the first time a negative regulatory role of Vγ1 γδ T cells in Vγ4 γδ T cell-mediated antitumor immunity through cell contact-independent and IL-4-mediated mechanisms. Selective depletion of this suppressive subset of γδ T cells may be beneficial for tumor immune therapy.

Prostaglandin I₂promotes the development of IL-17-producing γδ T cells that associate with the epithelium during allergic lung inflammation

γδ T cells rapidly produce cytokines and represent a first line of defense against microbes and other environmental insults at mucosal tissues and are thus thought to play a local immunoregulatory role. We show that allergic airway inflammation was associated with an increase in innate IL-17-producing γδ T (γδ-17) cells that expressed the αEβ7 integrin and were closely associated with the airway epithelium. Importantly, PGI(2) and its receptor IP, which downregulated airway eosinophilic inflammation, promoted the emergence of these intraepithelial γδ-17 cells into the airways by enhancing IL-6 production by lung eosinophils and dendritic cells. Accordingly, a pronounced reduction of γδ-17 cells was observed in the thymus of naive mice lacking the PGI(2) receptor IP, as well as in the lungs during allergic inflammation, implying a critical role for PGI(2) in the programming of "natural" γδ-17 cells. Conversely, iloprost, a stable analog of PGI(2), augmented IL-17 production by γδ T cells but significantly reduced airway inflammation. Together, these findings suggest that PGI(2) plays a key immunoregulatory role by promoting the development of innate intraepithelial γδ-17 cells through an IL-6-dependent mechanism. By enhancing γδ-17 cell responses, stable analogs of PGI(2) may be exploited in the development of new immunotherapeutic approaches.

Activated gammadelta T cells promote the activation of uveitogenic T cells and exacerbate EAU development

PURPOSE

To determine how the activation of γδ T cells affects the generation of uveitogenic αβ T cells and the development of experimental autoimmune uveitis (EAU).

METHODS

γδ T cells were isolated from B6 mice immunized with the uveitogenic peptide IRBP(1-20) and αβ T cells from immunized TCR-δ(-/-) mice. Resting γδ T cells were prepared by culture of separated γδ T cells in cytokine-free medium for 3 to 5 days, when they showed downregulation of CD69 expression. Activated γδ T cells were prepared by incubating resting γδ T cells with anti-γδ TCR (GL3) for 2 days. Responder αβ T cells were cocultured with immunizing antigen and antigen-presenting cells. The numbers of antigen-specific T cells expressing IL-17 or IFN-γ were determined by intracellular staining followed by FACS analysis after stimulation, with or without the addition of purified γδ T cells. The cytokines in the culture medium were measured by ELISA.

RESULTS

Highly enriched γδ T cells exert widely different effects on autoreactive αβ T cells in EAU, depending on the activation status of the γδ T cells. Whereas nonactivated γδ T cells had little effect on the activation of interphotoreceptor retinoid-binding protein-specific αβ T cells in vitro and in vivo, activated γδ T cells promoted the generation of uveitogenic T cells and exacerbated the development of EAU.

CONCLUSIONS

The functional ability of γδ T cells is greatly influenced by their activation status. Activated γδ T cells exacerbate EAU through increased activation of uveitogenic T 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.

Involvement of NK 1.1-positive γδT cells in interleukin-18 plus interleukin-2-induced interstitial lung disease

Interstitial lung disease (ILD) is induced by various factors in humans. However, the exact mechanism of ILD remains elusive. This study sought to determine the role of natural killer (NK) 1.1(+) γδT cells in ILD. The injection of IL-18 plus IL-2 (IL-18/IL-2) into C57BL6 (B6) mice induced acute ILD that resembled early-stage human ILD. An accumulation of NK1.1(+) γδT cells similar to NK cells was evident in the lungs. The T Cell Receptor (TCR) Vγ and Vδ repertoires of NK1.1(+) γδT cells indicated polyclonal expansion. The expression of IL-2 receptor β (Rβ) and IL-18Rβ in NK1.1(+) γδT cells was higher than in NK1.1(-) γδT cells. IL-18/IL-2 stimulated the proliferation of NK1.1(+) γδT cells, but not NK1.1(-) γδT cells. The IL-18/IL-2-stimulated NK1.1(+) γδT cells produced higher concentrations of IFN-γ than did NK1.1(-) γδT cells. Moreover, NK1.1(+) γδT and NK1.1(-) γδT cells constituted completely different cell populations. The IL-18/IL-2-induced ILD was milder in TCRδ(-/-) and IFN-γ(-/-) mice, compared with B6 mice. Furthermore, cell-transfer experiments demonstrated that NK1.1(+) γδT cells could induce the expansion of NK cells and IFN-γ mRNA in the lung by IL-18/IL-2. Our results suggest that NK1.1(+) γδT cells function as inflammatory mediators in the early phase of IL-18/IL-2-induced ILD.

γδ T cells develop, respond and survive - with a little help from CD27

Although the TNF receptor family member CD27 has been known for some time, its functional role as a coreceptor on T and B cells remains poorly understood. Recent reports have shown that CD27 and its ligand CD70 play a critical role in the development and function of γδ T cells in mice. In this issue of the European Journal of Immunology, a study now extends these findings to the Vγ9Vδ2(+) subset of human γδ T cells. This subset, whose responses are readily elicited by phosphoantigens, plays an important role in anti-tumor immune responses. This study shows that most Vγ9Vδ2(+) cells express CD27, and signaling via the CD27-CD70 axis is needed for their survival, proliferation and cytokine secretion. Moreover, CD27 functions as a coreceptor, which promotes, in conjunction with TCR-mediated signals, expansion of Th1-biased Vγ9Vδ2(+) cells. This new information underscores the significance of CD27 in γδ T-cell functional differentiation, and is likely to facilitate the development of γδ T-cell-based clinical immunotherapy.

Aerobiology and inhalation exposure to biological select agents and toxins

Aerosol is the most likely route of dissemination of biological select agents and toxins in a bioterrorist attack, regardless of the natural route of exposure to the agent. The use of animal models for testing preventative and therapeutic countermeasures requires knowledge of the pathogenesis of disease after inhalation exposure. Factors that relate to outcome after respiratory exposure include the inherent infectivity and virulence and/or toxicity of the agent in the host under investigation, in addition to characteristics of the aerosol particle and host that affect the delivered dose of, and host response to, the inhaled material. This introductory article discusses the emerging science of aerobiology and the unique features of respiratory tract anatomy, physiology, and immunology that are relevant to the pathogenesis of aerosolized biothreat agents.

Epidermal T cells and wound healing

The murine epidermis contains resident T cells that express a canonical gammadelta TCR. These cells arise from fetal thymic precursors and use a TCR that is restricted to the skin in adult animals. These cells assume a dendritic morphology in normal skin and constitutively produce low levels of cytokines that contribute to epidermal homeostasis. When skin is wounded, an unknown Ag is expressed on damaged keratinocytes. Neighboring gammadelta T cells then round up and contribute to wound healing by local production of epithelial growth factors and inflammatory cytokines. In the absence of skin gammadelta T cells, wound healing is impaired. Similarly, epidermal T cells from patients with healing wounds are activated and secreting growth factors. Patients with nonhealing wounds have a defective epidermal T cell response. Information gained on the role of epidermal-resident T cells in the mouse may provide information for development of new therapeutic approaches to wound healing.

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.

Naturally activated V gamma 4 gamma delta T cells play a protective role in tumor immunity through expression of eomesodermin

We previously demonstrated that gammadelta T cells played an important role in tumor immune surveillance by providing an early source of IFN-gamma. The precise role of different subsets of gammadelta T cells in the antitumor immune response, however, is unknown. Vgamma1 and Vgamma4 gammadelta T cells are the principal subsets of peripheral lymphoid gammadelta T cells and they might play distinct roles in tumor immunity. In support of this, we observed that reconstitution of TCRdelta(-/-) mice with Vgamma4, but not Vgamma1, gammadelta T cells restored the antitumor response. We also found that these effects were exerted by the activated (CD44(high)) portion of Vgamma4 gammadelta T cells. We further determined that IFN-gamma and perforin are critical elements in the Vgamma4-mediated antitumor immune response. Indeed, CD44(high) Vgamma4 gammadelta T cells produced significantly more IFN-gamma and perforin on activation, and showed greater cytolytic activity than did CD44(high) Vgamma1 gammadelta T cells, apparently due to the high level of eomesodermin (Eomes) in these activated Vgamma4 gammadelta T cells. Consistently, transfection of dominant-negative Eomes in Vgamma4 gammadelta T cells diminished the level of IFN-gamma secretion, indicating a critical role of Eomes in the effector function of these gammadelta T cells. Our results thus reveal distinct functions of Vgamma4 and Vgamma1 gammadelta T cells in antitumor immune response, and identify a protective role of activated Vgamma4 gammadelta T cells, with possible implications for tumor immune therapy.

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.

Krüppel-like factor 2 regulates trafficking and homeostasis of gammadelta T cells

gammadelta T cells are generated in the thymus and traffic to secondary lymphoid organs and epithelial surfaces, where they regulate immune responses. alphabeta T cells require sphingosine 1-phosphate receptor type 1 (S1P(1)) and CD62L for thymic emigration and circulation through secondary lymphoid organs. Both of these genes are regulated by the transcription factor Krüppel-like factor 2 (KLF2) in conventional alphabeta T cells. It is unclear if gammadelta T cells use similar mechanisms. In this study, we show that thymic gammadelta T cells express S1P(1) and that it is regulated by KLF2. Furthermore, KLF2 and S1P(1)-deficient gammadelta T cells accumulate in the thymus and fail to populate the secondary lymphoid organs or gut, in contrast to the expectation from published work. Interestingly, KLF2 but not S1P(1) deficiency led to the expansion of a usually rare population of CD4(+) promyelocytic leukemia zinc finger(+) "gammadelta NKT" cells. Thus, KLF2 is critically important for the homeostasis and trafficking of gammadelta T cells.

Resolution of allergic airway inflammation and airway hyperreactivity is mediated by IL-17-producing {gamma}{delta}T cells

RATIONALE

gammadeltaT lymphocytes are enriched within the epithelial microenvironment, where they are thought to maintain homeostasis and limit immunopathology. gammadeltaT cells are postulated to exert a regulatory influence during acute allergic airway disease, but the mechanism is unknown. Although regulation of allergic airway disease has been attributed to IL-17-producing T helper (Th) 17 cells, we have found that gammadeltaT cells represent the major source of IL-17 in the allergic lung.

OBJECTIVES

The aim of this study was to determine the contribution of these IL-17-producing gammadeltaT cells to regulation of allergic airway inflammation.

METHODS

Flow cytometry revealed that IL-17-producing gammadeltaT cells are more prevalent than IL-17(+)alphabetaT cells (Th17) in a murine model of ovalbumin-induced allergic inflammation.

MEASUREMENTS AND MAIN RESULTS

Transfer of gammadeltaT cells at the peak of acute allergic responses ameliorated airway hyperresponsiveness with a corresponding acceleration in the resolution of eosinophilic and Th2-driven inflammation. Conversely, functional blockade of gammadeltaT cells led to exacerbation of injury. Neither treatment changed pulmonary Th17 cell numbers. Moreover, transfer of Th17 cells had no effect on disease outcome. Importantly, IL-17-deficient gammadeltaT cells were unable to promote resolution of injury. These data identify IL-17-producing gammadeltaT cells as key regulators of the allergic response in vivo.

CONCLUSIONS

This unfolds a new perspective for the understanding of gammadeltaT cell function with regard to innate regulation of the adaptive immune responses, emphasizing that resolution of responses are important in determining the outcome of acute inflammatory episodes as well as for maintenance of tissue integrity and homeostasis.

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.

Gamma delta T cell receptors confer autonomous responsiveness to the insulin-peptide B:9-23

The range and physical qualities of molecules that act as ligands for the gammadelta T cell receptors (TCRs) remain uncertain. Processed insulin is recognized by alphabeta T cells, which mediate diabetes in non-obese diabetic (NOD) mice. Here, we present evidence that gammadelta T cells in these mice recognize processed insulin as well. Hybridomas generated from NOD spleen and pancreatic lymph nodes included clones expressing gammadelta TCRs that responded specifically to purified islets of Langerhans and to an insulin peptide, but not to intact insulin. The gammadelta TCRs associated with this type of response are diverse, but a cloned gammadelta TCR was sufficient to transfer the response. The response to the insulin peptide was autonomous as demonstrated by stimulating single responder cells in isolation. This study reveals a novel specificity for gammadelta TCRs, and raises the possibility that gammadelta T cells become involved in islet-specific autoimmunity.

Integrating WHO 2001-2008 criteria for the diagnosis of Myelodysplastic Syndrome (MDS): a case-case analysis of benzene exposure

We characterized the prevalence of hematopoietic and lymphoid disease for 2923 consecutive patients presenting at 29 hospitals from August 2003 to June 2007. Diagnoses were made in our laboratory using WHO criteria based on morphologic, immunophenotypic, cytogenetic, FISH and molecular data. A total of 611 subjects (322 males/289 females) were prospectively diagnosed with MDS using WHO (2001) criteria. Update and re-evaluation of cases using MDS (2008) criteria resulted in 649 MDS cases. Using WHO (2008) criteria, refractory cytopenia with multilineage dysplasia (RCMD) accounted for 68% of total cases, refractory anemia with excess blasts (RAEB), 16.3%; refractory anemia (RA), 6.5%; refractory cytopenia with unilineage dysplasia (RCUD), 4%; and MDS-unclassifiable (MDS-U), 4.5%. Subjects were administered questionnaires and information on previous disease, work histories and exposures to potential etiologic agents such as benzene (BZ) was obtained. A total of 80/649 (13.2%) were determined to have some BZ exposure. The frequency of clonal cytogenetic abnormalities in all MDS was 30%, the most common being +8>del(20)q>del(7q)>del(5q), while the analogous frequency in BZ-exposed cases was only 24%. To further investigate the characteristics of MDS associated with BZ, we identified a subset of cases with high BZ exposure. These BZ signal cases were each matched by age and gender to two cases with no known BZ exposure. When contrasting BZ signal cases vs matched cases with no BZ exposure, we found a high odds ratio (OR) for the WHO subtype MDS-U (OR=11.1), followed by RAEB and RCUD (OR=1), RA (OR=0.7) and RCMD (OR=0.6). Multilineage dysplasia with abnormal eosinophils (MDS-Eo) was strongly associated with BZ exposure, whereas the relative risk of clonal cytogenetic abnormalities was reduced for high BZ-exposed cases (OR=0.5). These findings are strongly indicative that MDS subtypes are influenced by BZ exposure, and taken together with previous studies, the features of MDS-Eo suggest that altered immune regulation plays a major role in the pathogenesis of MDS following chronic exposure to BZ.

Gammadelta T cells and Th17 cytokines in hypersensitivity pneumonitis and lung fibrosis

Hypersensitivity pneumonitis (HP) is an inflammatory lung disease caused by the repeated inhalation of aerosolized antigens. With chronic exposure to an inhaled antigen, patients are at risk of developing irreversible pulmonary fibrosis as well as an increased morbidity and mortality. Although alphabeta T cells have been shown to be important in the pathogenesis of HP, gammadelta T cells also accumulate in the bronchoalveolar lavage of patients with HP. gammadelta T cells represent a distinct lymphocyte subset, whose primary function is not well understood. In contrast to alphabeta T cells, gammadelta T cells recognize unprocessed antigens, such as those upregulated on injured or stressed epithelial cells. In a murine model of HP induced by exposure to the ubiquitous microorganism Bacillus subtilis, gammadelta T cells expressing the canonical Vgamma6/Vdelta1 T cell receptor were dramatically expanded in the lung. The predominant cytokines expressed by this gammadelta T-cell subset were T-helper 17 (Th17) cytokines that were critical for bacterial clearance and the resolution of lung inflammation. Th17-expressing gammadelta T cells are also expanded in other murine models of lung infection and inflammation, which suggests that these cells play a sentinel role in mucosal immunity. Thus, an increased understanding of gammadelta T cells that express Th17 cytokines in HP and other inflammatory lung diseases may lead to the development of novel therapeutic and clinical strategies that prevent the development of fibrotic lung disease.

The influence of IgE-enhancing and IgE-suppressive gammadelta T cells changes with exposure to inhaled ovalbumin

It has been reported that the IgE response to allergens is influenced by gammadelta T cells. Intrigued by a study showing that airway challenge of mice with OVA induces in the spleen the development of gammadelta T cells that suppress the primary IgE response to i.p.-injected OVA-alum, we investigated the gammadelta T cells involved. We found that the induced IgE suppressors are contained within the Vgamma4(+) subset of gammadelta T cells of the spleen, that they express Vdelta5 and CD8, and that they depend on IFN-gamma for their function. However, we also found that normal nonchallenged mice harbor IgE-enhancing gammadelta T cells, which are contained within the larger Vgamma1(+) subset of the spleen. In cell transfer experiments, airway challenge of the donors was required to induce the IgE suppressors among the Vgamma4(+) cells. Moreover, this challenge simultaneously turned off the IgE enhancers among the Vgamma1(+) cells. Thus, airway allergen challenge differentially affects two distinct subsets of gammadelta T cells with nonoverlapping functional potentials, and the outcome is IgE suppression.

Enhanced development of CD4+ gammadelta T cells in the absence of Itk results in elevated IgE production

The Tec kinase Itk is critical for the development of alphabeta T cells as well as differentiation of CD4(+) T cells into Th2 cells. Itk null mice have defects in the production of Th2 cytokines; however, they paradoxically have significant elevations in serum IgE. Here we show that Itk null mice have increased numbers of gammadelta T cells in the thymus and spleen. This includes elevated numbers of CD4(+) gammadelta T cell, the majority of which carry the Vgamma1.1 and Vdelta6.2/3 gammadelta T-cell receptor with a distinct phenotype. The development of these CD4(+) gammadelta T cells is T cell intrinsic, independent of either major histocompatibility complex class I or class II, and is favored during development in the absence of Itk. Itk null CD4(+) gammadelta T cells secrete significant amounts of Th2 cytokines and can induce the secretion of IgE by wild-type B cells. Our data indicate that Itk plays important role in regulating gammadelta T-cell development and function. In addition, our data indicate that the elevated IgE observed in Itk-deficient mice is due in part to the enhanced development of CD4(+) gammadelta T cells in the absence of Itk.

Allergic airway hyperresponsiveness-enhancing gammadelta T cells develop in normal untreated mice and fail to produce IL-4/13, unlike Th2 and NKT cells

Allergic airway hyperresponsiveness (AHR) in OVA-sensitized and challenged mice, mediated by allergen-specific Th2 cells and Th2-like invariant NKT (iNKT) cells, develops under the influence of enhancing and inhibitory gammadelta T cells. The AHR-enhancing cells belong to the Vgamma1(+) gammadelta T cell subset, cells that are capable of increasing IL-5 and IL-13 levels in the airways in a manner like Th2 cells. They also synergize with iNKT cells in mediating AHR. However, unlike Th2 cells, the AHR enhancers arise in untreated mice, and we show here that they exhibit their functional bias already as thymocytes, at an HSA(high) maturational stage. In further contrast to Th2 cells and also unlike iNKT cells, they could not be stimulated to produce IL-4 and IL-13, consistent with their synergistic dependence on iNKT cells in mediating AHR. Mice deficient in IFN-gamma, TNFRp75, or IL-4 did not produce these AHR-enhancing gammadelta T cells, but in the absence of IFN-gamma, spontaneous development of these cells was restored by adoptive transfer of IFN-gamma-competent dendritic cells from untreated donors. The i.p. injection of OVA/aluminum hydroxide restored development of the AHR enhancers in all of the mutant strains, indicating that the enhancers still can be induced when they fail to develop spontaneously, and that they themselves need not express TNFRp75, IFN-gamma, or IL-4 to exert their function. We conclude that both the development and the cytokine potential of the AHR-enhancing gammadelta T cells differs critically from that of Th2 cells and NKT cells, despite similar influences of these cell populations on AHR.

Requirement of L-selectin for gammadelta T lymphocyte activation and migration during allergic pleurisy: co-relation with eosinophil accumulation

Intra-thoracic antigenic challenge (ovalbumin, 12.5 microg/cavity) led to increased numbers of gammadelta T lymphocytes in pleural cavities, blood and thoracic lymph nodes in sensitized mice within 48 h. Part of these cells expressed CD62L, which increased on gammadelta T cell surfaces obtained from lymph nodes after ovalbumin (OVA) challenge. Selectin blockade by fucoidan pre-treatment (10 mg/kg, i.v.) impaired in vivo increase in CD25(+) and c-fos(+) gammadelta T cell numbers in lymph nodes, indicating a role for selectins on gammadelta T lymphocyte activation and proliferation. In vivo selectin blockade by fucoidan or alpha-CD62L mAb (200 microg/mice, i.p.) also inhibited OVA-induced gammadelta T cell accumulation in pleural cavities. Confirming the direct effect of CD62L on gammadelta T cell transmigration, the migration of i.v. adoptively-transferred CFSE-labeled gammadelta T lymphocytes into pleural cavities of challenged recipient mice was impaired by fucoidan ex vivo treatment. It is noteworthy that eosinophil influx was also impaired in those mice, indicating that reduced eosinophil migration by CD62L in vivo blockade depended on gammadelta T cell migration via CD62L molecules. Accordingly, pleural gammadelta T lymphocytes from fucoidan-treated mice presented reduced OVA-induced IL-5 and CCL11 production. Supporting these data, the depletion of Vgamma4 T lymphocytes, which are pulmonary gammadelta T cells, decreased OVA-induced eosinophil influx into allergic site. Such results demonstrate that CD62L is crucial for the activation of gammadelta T cells in lymph nodes, for their migration into inflamed tissue and for the modulation of eosinophil influx during allergic response.

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.

Vgamma1+ T cells and tumor necrosis factor-alpha in ozone-induced airway hyperresponsiveness

gammadelta T cells regulate airway reactivity, but their role in ozone (O3)-induced airway hyperresponsiveness (AHR) is not known. Our objective was to determine the role of gammadelta T cells in O3-induced AHR. Different strains of mice, including those that were genetically manipulated or antibody-depleted to render them deficient in total gammadelta T cells or specific subsets of gammadelta T cells, were exposed to 2.0 ppm of O3 for 3 hours. Airway reactivity to inhaled methacholine, airway inflammation, and epithelial cell damage were monitored. Exposure of C57BL/6 mice to O3 resulted in a transient increase in airway reactivity, neutrophilia, and increased numbers of epithelial cells in the lavage fluid. TCR-delta(-/-) mice did not develop AHR, although they exhibited an increase in neutrophils and epithelial cells in the lavage fluid. Similarly, depletion of gammadelta T cells in wild-type mice suppressed O3-induced AHR without influencing airway inflammation or epithelial damage. Depletion of Vgamma1+, but not of Vgamma4+ T cells, reduced O3-induced AHR, and transfer of total gammadelta T cells or Vgamma1+ T cells to TCR-delta(-/-) mice restored AHR. After transfer of Vgamma1+ cells to TCR-delta(-/-) mice, restoration of AHR after O3 exposure was blocked by anti-TNF-alpha. However, AHR could be restored in TCR-delta(-/-)mice by transfer of gammadelta T cells from TNF-alpha-deficient mice, indicating that another cell type was the source of TNF-alpha. These results demonstrate that TNF-alpha and activation of Vgamma1+ gammadelta T cells are required for the development of AHR after O3 exposure.

Vγ1+ γδ T cells reduce IL-10-producing CD4+CD25+ T cells in the lung of ovalbumin-sensitized and challenged mice

In OVA-sensitized and challenged mice, gammadelta T cells expressing Vgamma1 enhance airway hyperresponsiveness (AHR) but the underlying mechanism is unclear. These cells also reduce IL-10 levels in the airways, suggesting that they might function by inhibiting CD4(+)CD25(+) regulatory T cells (T(reg)) or other CD4(+) T cells capable of producing IL-10 and suppressing AHR. Indeed, sensitization and challenge with OVA combined with inactivation of Vgamma1(+) cells increased CD4(+)CD25(+) cells in the lung, and markedly those capable of producing IL-10. The cellular change was associated with increased IL-10 and TGF-beta levels in the airways, and a decrease of IL-13. T(reg) include naturally occurring Foxp3(+) T(reg), inducible Foxp3(-) T(reg), and antigen-specific T(reg) many of which express folate receptor 4 (FR4). Although Foxp3 gene expression in the lung was also increased pulmonary CD4(+) T cells, expressing Foxp3-protein or FR4 remained stable. Therefore, the inhibition by Vgamma1(+) gammadelta T cells might not be targeting Foxp3(+) T(reg) but rather CD4(+) T cells destined to produce IL-10.

A subset of IL-10-producing gammadelta T cells protect the liver from Listeria-elicited, CD8(+) T cell-mediated injury

Although gammadelta T cells play a role in protecting tissues from pathogen-elicited damage to bacterial, viral and parasitic pathogens, the mechanisms involved in the damage and in the protection have not been clearly elucidated. This has been addressed using a murine model of listeriosis, which in mice lacking gammadelta T cells (TCRdelta(-/-)) is characterised by severe and extensive immune-mediated hepatic necrosis. We show that these hepatic lesions are caused by Listeria-elicited CD8(+) T cells secreting high levels of TNF-alpha that accumulate in the liver of Listeria-infected TCRdelta(-/-) mice. Using isolated populations of gammadelta T cells from wild-type and cytokine-deficient strains of mice to reconstitute TCRdelta(-/-) mice, the TCR variable gene 4 (Vgamma4)(+) subset of gammadelta T cells was shown to protect against liver injury. Hepatoprotection was dependent upon their ability to produce IL-10 after TCR-mediated interactions with Listeria-elicited macrophages and CD8(+) T cells. IL-10-producing Vgamma4(+) T cells also contribute to controlling CD8(+) T cell expansion and to regulating and reducing TNF-alpha secretion by activated CD8(+) T cells. This effect on TNF-alpha production was directly attributed to IL-10. These findings identify a novel mechanism by which pathogen-elicited CD8(+) T cells are regulated via interactions with, and activation of, IL-10-producing hepatoprotective gammadelta T cells.

Characterization and TCR variable region gene use of mouse resident nasal gammadelta T lymphocytes

Tissue-resident gammadelta T lymphocytes, such as dendritic epidermal T cells, intestinal intraepithelial lymphocytes (IEL), and resident pulmonary lymphocytes, are known to support local tissue homeostasis and host defense. Inhaled antigens, toxins, and microorganisms first interact with the immune system through contact with the nasal mucosa. Herein, we characterized two populations of resident nasal lymphocytes (RNL) that are present in the nasal mucosa: nasal IEL (nIEL) and nasal lamina propria lymphocytes (nLPL). gammadelta TCR+ and alphabeta TCR+ nIEL and nLPL were detected by immunofluorescent staining. Mononuclear cells (5-15%) were CD3+ RNL by FACS analysis. Among the CD3+ RNL, 20-30% were GL3+ gammadelta T cells, which were double-negative for CD4 and CD8 and predominantly expressed a Vgamma4/Vdelta1 TCR. These results demonstrate that RNL might be crucial for the host defense and tissue homeostasis in the nasal mucosa.

Evidence that CD8+ dendritic cells enable the development of gammadelta T cells that modulate airway hyperresponsiveness

Airway hyperresponsiveness (AHR), a hallmark of asthma and several other diseases, can be modulated by gammadelta T cells. In mice sensitized and challenged with OVA, AHR depends on allergen-specific alphabeta T cells; but Vgamma1+ gammadelta T cells spontaneously enhance AHR, whereas Vgamma4+ gammadelta T cells, after being induced by airway challenge, suppress AHR. The activity of these gammadelta T cell modulators is allergen nonspecific, and how they develop is unclear. We now show that CD8 is essential for the development of both the AHR suppressor and enhancer gammadelta T cells, although neither type needs to express CD8 itself. Both cell types encounter CD8-expressing non-T cells in the spleen, and their functional development in an otherwise CD8-negative environment can be restored with transferred spleen cell preparations containing CD8+ dendritic cells (DCs), but not CD8+ T cells or CD8- DCs. Our findings suggest that CD8+ DCs in the lymphoid tissues enable an early step in the development of gammadelta T cells through direct cell contact. DC-expressed CD8 might take part in this interaction.

Role of two distinct gammadelta T cell subsets during West Nile virus infection

gammadelta T cells respond rapidly following West Nile virus (WNV) infection, limiting viremia and invasion of the central nervous system and thereby protecting the host from lethal encephalitis. Here, we investigated the role of two major subpopulations of peripheral gammadelta T cells, Vgamma1(+) and Vgamma4(+) cells, in host immunity against WNV infection. We found initially that aged mice were more susceptible to WNV infection than young mice. Following WNV challenge, Vgamma1(+) cells in young mice expanded significantly whereas Vgamma4(+) cells expanded modestly. In contrast, aged mice exhibited a slower and reduced response of Vgamma1(+) cells but maintained a higher content of Vgamma4(+) cells. Vgamma1(+) cells were the major gammadelta subset producing IFN-gamma during WNV infection. Mice depleted of Vgamma1(+) cells had an enhanced viremia and higher mortality to WNV encephalitis. Vgamma4(+) cells had a higher potential for producing tumor necrosis factor-alpha (TNF-alpha), a cytokine known to be involved in blood-brain barrier compromise and WNV entry into the brain. Depletion of Vgamma4(+) cells reduced TNF-alpha level in the periphery, accompanied by a decreased viral load in the brain and a lower mortality to WN encephalitis. These results suggest that Vgamma1(+) and Vgamma4(+) cells play distinct roles in protection and pathogenesis during WNV infection.

Evidence for the involvement of lung-specific gammadelta T cell subsets in local responses to Streptococcus pneumoniae infection

Although γδ T cells are involved in the response to many pathogens, the dynamics and heterogeneity of the local γδ T cell response remains poorly defined. We recently identified γδ T cells as regulators of macrophages and dendritic cells during the resolution of Streptococcus pneumoniae-mediated lung inflammation. Here, using PCR, spectratype analysis and flow cytometry, we show that multiple γδ T cell subsets, including those bearing Vγ1, Vγ4 and Vγ6 TCR, increase in number in the lungs of infected mice, but not in associated lymphoid tissue. These γδ T cells displayed signs of activation, as defined by CD69 and CD25 expression. In vivo BrdU incorporation suggested that local expansion, rather than recruitment, was the principal mechanism underlying this increase in γδ T cells. This conclusion was supported by the finding that pulmonary γδ T cells, but not αβ T cells, isolated from mice that had resolved infection exhibited lung-homing capacity in both naive and infected recipients. Together, these data provide novel insights into the origins of the heterogeneous γδ T cell response that accompanies lung infection, and the first evidence that inflammation-associated γδ T cells may exhibit distinct tissue-homing potential.

Involvement of CC chemokines in gammadelta T lymphocyte trafficking during allergic inflammation: the role of CCL2/CCR2 pathway

In the present study, we show that the intra-thoracic injection of ovalbumin (OVA, 12.5 microg per cavity) into C57BL/10 mice induced a significant increase in gammadelta T lymphocyte numbers in the pleural cavity, blood and thoracic lymph node of challenged mice. Such increase was significant within 12 h, peaked within 48 h and returned to basal counts within 120 h. Levels of CC chemokine ligand (CCL)-2/monocyte chemotactic protein-1, CCL5/regulated upon activation, normal T cell expressed and secreted, CCL3/macrophage inflammatory protein-1 alpha and CCL25/thymus-expressed chemokine were above control values in pleural washes recovered 24 h after OVA challenge (OPW) and were likely produced by pleural macrophages and mesothelial cells. Antigenic challenge also induced an up-regulation in CC chemokine receptor (CCR)-2, CCR5 and CCR9 on gammadelta T cells from pleural cavities, blood and lymph nodes, suggesting that cells found in mice pleural cavity migrate from secondary lymphoid organs into the inflammatory site via blood stream. The in vitro neutralization of CCL2 (but not of CCL3, CCL5 or CCL25) abrogated OPW-induced gammadelta T lymphocyte transmigration. Confirming such results, the in vivo administration of alpha-CCL2 mAb inhibited gammadelta T lymphocyte accumulation in the pleural cavity of challenged mice, whereas the blockade of CCL3, CCL5 or CCL25 showed no effect on gammadelta T cell mobilization. In addition, OVA challenge failed to induce gammadelta T lymphocyte accumulation in the pleural cavity of C57BL/6 CCR2 knockout mice, which also showed decreased numbers of these cells in blood and lymph nodes when compared with wild-type mice. Overall, such results demonstrate that CCR2/CCL2 pathway is crucial for gammadelta T lymphocyte mobilization during the allergic response.

Exacerbation of collagen-induced arthritis by oligoclonal, IL-17-producing gamma delta T cells

Murine gammadelta T cell subsets, defined by their Vgamma chain usage, have been shown in various disease models to have distinct functional roles. In this study, we examined the responses of the two main peripheral gammadelta T cell subsets, Vgamma1(+) and Vgamma4(+) cells, during collagen-induced arthritis (CIA), a mouse model that shares many hallmarks with human rheumatoid arthritis. We found that whereas both subsets increased in number, only the Vgamma4(+) cells became activated. Surprisingly, these Vgamma4(+) cells appeared to be Ag selected, based on preferential Vgamma4/Vdelta4 pairing and very limited TCR junctions. Furthermore, in both the draining lymph node and the joints, the vast majority of the Vgamma4/Vdelta4(+) cells produced IL-17, a cytokine that appears to be key in the development of CIA. In fact, the number of IL-17-producing Vgamma4(+) gammadelta T cells in the draining lymph nodes was found to be equivalent to the number of CD4(+)alphabeta(+) Th-17 cells. When mice were depleted of Vgamma4(+) cells, clinical disease scores were significantly reduced and the incidence of disease was lowered. A decrease in total IgG and IgG2a anti-collagen Abs was also seen. These results suggest that Vgamma4/Vdelta4(+) gammadelta T cells exacerbate CIA through their production of IL-17.

Airway hyperresponsiveness through synergy of gammadelta} T cells and NKT cells

Mice sensitized and challenged with OVA were used to investigate the role of innate T cells in the development of allergic airway hyperresponsiveness (AHR). AHR, but not eosinophilic airway inflammation, was induced in T cell-deficient mice by small numbers of cotransferred gammadelta T cells and invariant NKT cells, whereas either cell type alone was not effective. Only Vgamma1+Vdelta5+ gammadelta T cells enhanced AHR. Surprisingly, OVA-specific alphabeta T cells were not required, revealing a pathway of AHR development mediated entirely by innate T cells. The data suggest that lymphocytic synergism, which is key to the Ag-specific adaptive immune response, is also intrinsic to T cell-dependent innate responses.

Arhgef1 is required by T cells for the development of airway hyperreactivity and inflammation

RATIONALE

Arhgef1 is an intracellular protein, expressed by hematopoietic cells, that regulates signaling by both G protein-coupled receptors and RhoA, and, consequently, is required for appropriate migration and adhesion of diverse leukocyte populations.

OBJECTIVES

To evaluate a possible contribution for Arhgef1 in the development of airway inflammation and airway hyperreactivity.

METHODS

Arhgef1-deficient (Arhgef1-/-) and wild-type (WT) mice were sensitized and airway challenged, followed by measurement of airway responsiveness to inhaled methacholine. Inflammation was assessed by several parameters that included flow cytometric analysis and histology. Arhgef1-deficient recipients were reconstituted with WT T lymphocytes before sensitization and challenge, and again measured for airway responsiveness and inflammation. Cytokine production in response to specific antigen was measured in cultures of isolated leukocytes from lung and spleen and compared with the levels generated in lung and spleen explant cultures.

MEASUREMENTS AND MAIN RESULTS

Arhgef1-/- mice display significantly reduced airway hyperreactivity, Th2 cytokine production, and lung inflammation, despite intact systemic immunity. After airway challenge of Arhgef1-/- mice, antigen-specific T cells were present in mutant lungs, but were found to interact with CD11c+ cells at a significantly reduced frequency. Adoptive transfer of WT T cells into Arhgef1-/- mice restored airway hyperreactivity and inflammation.

CONCLUSIONS

These data demonstrate that T cells depend on Arhgef1 to promote lung inflammation. Moreover, a deficiency in Arhgef1 results in reduced T cell-CD11c+ antigen-presenting cell interaction, and likely underscores the inability of Arhgef1-/- mice to mount an adaptive immune response to airway challenge.

gammadelta T lymphocytes-selectable cells within the innate system?

Lymphocytes expressing gammadelta T cell receptors (TCR) constitute an entire system of functionally specialized subsets that have been implicated in the regulation of immune responses, including responses to pathogens and allergens, and in tissue repair. The gammadelta TCRs share structural features with adaptive receptors and peripheral selection of gammadelta T cells occurs. Nevertheless, their specificities may be primarily directed at self-determinants, and the responses of gammadelta T cells exhibit innate characteristics. Continuous cross talk between gammadelta T cells and myeloid cells is evident in histological studies and in in vitro co-culture experiments, suggesting that gammadelta T cells play a functional role as an integral component of the innate immune system.

Antigen recognition by γδ T cells

gammadelta T cells contribute to host immune competence uniquely. This is most likely because they have distinctive antigen-recognition properties. While the basic organization of gammadelta T-cell receptor (TCR) loci is similar to that of alphabeta TCR loci, there is a striking difference in how the diversity of gammadelta TCRs is generated. gammadelta and alphabeta T cells have different antigen-recognition requirements and almost certainly recognize a different set of antigens. While it is unclear what most gammadelta T cells recognize, the non-classical major histocompatibility complex class I molecules T10 and T22 were found to be the natural ligands for a sizable population (0.2-2%) of murine gammadelta T cells. The recognition of T10/T22 may be a way by which gammadelta T cells regulate cells of the immune system, and this system has been used to determine the antigen-recognition determinants of gammadelta T cells. T10/T22-specific gammadelta T cells have TCRs that are diverse in both V gene usage and CDR3 sequences. Their Vgamma usage reflects their tissue origin, and their antigen specificity is conferred by a motif in the TCR delta chain that is encoded by V and D segments and by P-nucleotide addition. Sequence variations around this motif modulate affinities between TCRs and T10/T22. That this CDR3 motif is important in antigen recognition is confirmed by the crystal structure of a gammadelta TCR bound to its ligand. The significance of these observations is discussed in the context of gammadelta T-cell biology.

Accumulation of gamma/delta T cells in the lungs and their roles in neutrophil-mediated host defense against pneumococcal infection

The present study was designed to elucidate the role of Vgamma4(+) gammadelta T cells, a major subset of pulmonary gammadelta T cells, in host defense against infection with Streptococcus pneumoniae. The proportion and number of whole gammadelta T cells, identified as CD3(+) and TCR-delta(+) cells, and Vgamma4(+) gammadelta T cells, identified as CD3(+) and TCR-Vgamma4(+) cells, increased in the lungs at 3, 6 and 12h post-infection. Survival of infected mice and lung bacterial clearance were severely impaired in TCR-Vgamma4(-/-) mice compared with control wild-type (WT) mice. The impaired host protection in TCR-Vgamma4(-/-) mice correlated well with attenuated recruitment of neutrophils in lungs. MIP-2 and TNF-alpha synthesis in the infected tissues was significantly reduced in TCR-Vgamma4(-/-) mice compared with WT mice. Similar results were noted in the synthesis of TNF-alpha, but not clearly of MIP-2, by lung leukocytes stimulated with live bacteria. Our results demonstrate that Vgamma4(+) gammadelta T cells play an important role in the neutrophil-mediated host defense against S. pneumoniae infection by promoting the synthesis of TNF-alpha and possibly of MIP-2 in the lungs.

Regulatory role of gammadelta T cells in the recruitment of CD4+ and CD8+ T cells to lung and subsequent pulmonary fibrosis

The mechanisms by which T cells accumulate in the lungs of patients with pulmonary fibrosis are poorly understood. Because the lung is continually exposed to microbial agents from the environment, we repeatedly exposed C57BL/6 mice to the ubiquitous microorganism, Bacillus subtilis, to determine whether chronic exposure to an inhaled microorganism could lead to T cell accumulation in the lungs and subsequent pulmonary fibrosis. C57BL/6 mice repeatedly treated with B. subtilis for 4 consecutive weeks developed a 33-fold increase in the number of CD4+ T cells and a 354-fold increase in gammadelta T cells in the lung. The gammadelta T cells consisted almost entirely of Vgamma6/Vdelta1+ cells, a murine subset bearing an invariant TCR the function of which is still unknown. Treatment of C57BL/6 mice with heat-killed vs live B. subtilis resulted in a 2-fold increase in the number of CD4+ T cells in the lung but no expansion of gammadelta T cells indicating that gammadelta cells accumulate in response to live microorganisms. In addition, mice treated with heat-killed B. subtilis developed significantly increased pulmonary fibrosis compared with mice treated with the live microorganism. Mice deficient in Vgamma6/Vdelta1+ T cells when treated with B. subtilis had a 231-fold increase in lung CD4+ T cells and significantly increased collagen deposition compared with wild-type C57BL/6 mice, consistent with an immunoregulatory role for the Vgamma6/Vdelta1 T cell subset. These findings indicate that chronic inhalation of B. subtilis can result in T cell accumulation in the lung and fibrosis, constituting a new model of immune-mediated pulmonary fibrosis.

γδ T cells — innate immune lymphocytes?

It is unclear what the antigen recognition determinants of gammadelta T-cell receptors (TCRs) are. Compared with immunoglobulin and alphabeta TCRs, gammadelta TCRs have the highest potential CDR3 diversity generated by VDJ recombination. However, gammadelta T-cell reactivities seem to segregate with V gene usage, which has been taken to suggest that rearrangement has little role in generating different antigen specificities. During the past year, the CDR3 regions were found to determine the antigen specificities of T10- and T22-reactive gammadelta TCRs, a surface protein complex was identified as a ligand for human phosphoantigen-reactive gammadelta T cells, and the first co-crystal structure of a gammadelta TCR bound to its ligand was reported. These advances warrant a fresh look at gammadelta T-cell antigen recognition.

Evidence for the opposing roles of different gamma delta T cell subsets in macrophage homeostasis

To ensure invading pathogens are eliminated with minimal damage to host tissues it is essential that macrophage activation be tightly regulated. Previously we demonstrated that a subset of gammadelta T cells (Vgamma1(+)) contributes to resolving pathogen-induced immune responses by killing activated macrophages. However, the exaggerated macrophage response seen in infected Vgamma1(+) T cell-deficient mice suggests that gammadelta T cells play a broader role in macrophage homeostasis and other subsets might promote macrophage activation. Using a macrophage:gammadelta T cell co-culture system we have shown that gammadelta T cells increase the activity of macrophages activated in vivo by Listeria monocytogenes infection. In a dose-dependent manner, gammadelta T cells up-regulated production of cytokines (TNF-alpha, IL-6, IL-10) and chemokines (MIP-1alpha, MIP-1beta) by Listeria-elicited macrophages. The ability to increase macrophage cytokine production was prominent among Vgamma4(+) gammadelta T cells. Reciprocally, Vgamma4(+) gammadelta T cells were activated by Listeria-elicited macrophages, resulting in production of the anti-inflammatory cytokine, IL-10. gammadelta T cell adoptive transfer experiments showed that Vgamma4(+) T cells protected TCRdelta(-/-) mice against Listeria-induced liver injury and necrosis. These findings identify distinct and non-overlapping roles for gammadelta T cell subsets in regulating macrophage function during pathogen-induced immune responses.

Epithelial and mucosal gamma delta T cells

Although they constitute a small part of the circulating lymphocyte population, gammadelta T cells are found in high abundance on mucosal and epithelial surfaces. These gammadelta T cells are activated in response to stress to the surrounding tissue and perform a number of functions depending upon the location and type of stress that has occurred. Roles elucidated recently for gammadelta T cells include modulation of epithelial homeostasis through insulin-like growth factor-1 and keratinocyte growth factor, lysis of cytomegalovirus-infected cells, and recruitment of inflammatory cells to sites of tissue damage. Recent advances have provided an understanding of the development of mucosal and skin gammadelta T cells and their roles in restoring and maintaining tissue integrity.