Murine γδ T cells in infections: beneficial or deleterious?

A Retrospective Analysis of γδ T Cell Expression in Chronic Rhinosinusitis and Its Association with Recurrence of Nasal Polyps

BACKGROUND/AIMS

To examine whether γδ T cell is expressed in the nasal mucosa of chronic rhinosinusitis (CRS) patients and its potential association with recurrence of nasal polyps.

METHODS

Thirty-six patients with CRS with nasal polyps (CRSwNP) and 25 patients with CRS without nasal polyps (CRSsNP) were recruited. Twenty-six patients with other nasal diseases served as controls. The CRSwNP group was divided into the eosinophilic CRSwNP and noneosinophilic CRSwNP groups. The expression of γδ T cells was detected by immunohistochemistry. The expression of each subtype of γδ T cells was detected by using qRT-PCR. All patients underwent nasal endoscopy, and postoperative follow-up lasted over 12 months. CRS patients were evaluated by preoperative VAS scores of symptoms and nasal endoscopy Lund-Kennedy scores.

RESULTS

The expression of γδ T cells in the CRSwNP groups was stronger than in the CRSsNP and the control group (p < 0.05, p < 0.05). The expression of Vγ1+γδ T cells in the eosinophilic CRSwNP group was higher than that in the CRSsNP group and the control group (p < 0.05, p < 0.05). The expression of γδ T cells was associated with high rate of recurrence, tissue eosinophil infiltration, worse symptom score of nasal obstruction, and higher Lund-Kennedy score (all p < 0.05).

CONCLUSIONS

Increased expression of γδ T cells in CRSwNP may be associated with recurrence of nasal polyps.

Role of circulating lymphocytes in patients with sepsis

Sepsis is a systemic inflammatory response syndrome due to infection. The incidence rate is estimated to be up to 19 million cases worldwide per year and the number of cases is rising. Infection triggers a complex and prolonged host response, in which both the innate and adaptive immune response are involved. The disturbance of immune system cells plays a key role in the induction of abnormal levels of immunoregulatory molecules. Furthermore, the involvement of effector immune system cells also impairs the host response to the infective agents and tissue damage. Recently, postmortem studies of patients who died of sepsis have provided important insights into why septic patients die and showed an extensive depletion of CD4 and CD8 lymphocytes and they found that circulating blood cells showed similar findings. Thus, the knowledge of the characterization of circulating lymphocyte abnormalities is relevant for the understanding of the sepsis pathophysiology. In addition, monitoring the immune response in sepsis, including circulating lymphocyte subsets count, appears to be potential biomarker for predicting the clinical outcome of the patient. This paper analyzes the lymphocyte involvement and dysfunction found in patients with sepsis and new opportunities to prevent sepsis and guide therapeutic intervention have been revealed.

Intestinal intraepithelial lymphocyte-enterocyte crosstalk regulates production of bactericidal angiogenin 4 by Paneth cells upon microbial challenge

Antimicrobial proteins influence intestinal microbial ecology and limit proliferation of pathogens, yet the regulation of their expression has only been partially elucidated. Here, we have identified a putative pathway involving epithelial cells and intestinal intraepithelial lymphocytes (iIELs) that leads to antimicrobial protein (AMP) production by Paneth cells. Mice lacking γδ iIELs (TCRδ(-/-)) express significantly reduced levels of the AMP angiogenin 4 (Ang4). These mice were also unable to up-regulate Ang4 production following oral challenge by Salmonella, leading to higher levels of mucosal invasion compared to their wild type counterparts during the first 2 hours post-challenge. The transfer of γδ iIELs from wild type (WT) mice to TCRδ(-/-) mice restored Ang4 production and Salmonella invasion levels were reduced to those obtained in WT mice. The ability to restore Ang4 production in TCRδ(-/-) mice was shown to be restricted to γδ iIELs expressing Vγ7-encoded TCRs. Using a novel intestinal crypt co-culture system we identified a putative pathway of Ang4 production initiated by exposure to Salmonella, intestinal commensals or microbial antigens that induced intestinal epithelial cells to produce cytokines including IL‑23 in a TLR-mediated manner. Exposure of TCR-Vγ7(+) γδ iIELs to IL-23 promoted IL‑22 production, which triggered Paneth cells to secrete Ang4. These findings identify a novel role for γδ iIELs in mucosal defence through sensing immediate epithelial cell cytokine responses and influencing AMP production. This in turn can contribute to the maintenance of intestinal microbial homeostasis and epithelial barrier function, and limit pathogen invasion.

A divergent response of innate regulatory T-cells to sepsis in humans: circulating invariant natural killer T-cells are preserved

BACKGROUND

Sepsis is associated with severe immunosuppression, evidenced by loss and dysfunction of CD3(+) lymphocytes and γδ-TCR(+) T-cells. There is limited data addressing changes in the invariant natural killer T-(iNKT) cell population with sepsis, and whether such changes correlate with clinical outcomes. Specifically, septic geriatric patients have marked mortality. How γδ-TCR(+) T-cells and iNKT-cells are altered in the settings of sepsis and advanced age, and how these changes correlate with mortality are unknown.

METHODS

49 young (18-50years) and 55 geriatric (>65years) ICU patients with confirmed sepsis were enrolled. Blood was stained with antibodies to detect the percentage and absolute number of CD3(+) (T-cells), γδ-TCR(+) T-cell, TCR-Vα-24(+) (iNKT-cells), and CD69(+) (marker of cell activation). Blood from 10 healthy controls was also collected.

RESULTS

Septic patients displayed marked leukocytosis, decreased CD3(+) lymphocytes, and γδ-TCR(+) T-cells, and increased percentage and number of iNKT-cells. Young and geriatric patients had similar degree of leukocytosis, along with percentage, number, and %CD69(+) CD3(+) T-cell and γδ-TCR(+) T-cells; however, percentage, number, and %CD69(+)iNKT-cells were most markedly elevated in geriatric patients. Geriatric non-survivors had higher percentage and number of, but decreased %CD69(+), iNKT-cells vs survivors.

CONCLUSIONS

iNKT-cells are increased in sepsis, suggesting that they typify an evolving morbid state. This is most pronounced in geriatric non-survivors, a group demonstrating dysfunctional regulatory iNKT-cell phenotype.

Differentiation and activation of γδ T Lymphocytes: Focus on CD27 and CD28 costimulatory receptors

γδ T lymphocytes are major providers of the pro-inflammatory cytokines interferon-γ (IFN-γ) and interleukin-17 (IL-17) at early stages of (auto)immune responses. We and others have recently described the phenotype and differentiation requirements of two distinct murine γδ T cell subsets producing either IFN-γ or IL-17. Here we summarize our current understanding of the molecular mechanisms that control γδ T cell differentiation, which is programmed in the thymus, and peripheral activation upon infection. We focus on the costimulatory receptors CD27 and CD28, which play independent and non-redundant roles in the physiology of γδ T cells in mice and in humans.

Tolerizing allergic responses in the lung

The absolute requirement of the pulmonary immune system is to limit the inflammatory consequences of inhaled infectious agents while maintaining tolerance to harmless aeroallergens. This tolerance is maintained by a complex network of cells and molecules interacting with lung stromal cells. However, in some individuals there is a breakdown in tolerance to particles such as pollens, animal dander, or dust, resulting in the development of allergic pathology. Emerging evidence suggests that this breakdown in tolerance is influenced by the genetic background of individuals as well as environmental considerations such as early exposure to respiratory pathogens. Further understanding of the mechanisms used by the pulmonary immune system to maintain tolerance might result in exploitation of novel avenues for therapy to treat the growing number of chronic asthmatic patients.

A role for the mevalonate pathway in the induction of subtype cross-reactive immunity to influenza A virus by human gammadelta T lymphocytes

The major gammadelta T cell subset in the human peripheral blood expresses the Vgamma9delta2 TCR and recognizes non-peptidic prenyl pyrophosphate antigens such as isopentylpyrophosphate (IPP). Upon activation the gammadelta T cells rapidly secrete antiviral cytokines similar to classical memory alphabeta T cells. Here we have investigated the ability of gammadelta T lymphocytes from human PBMC to become activated by influenza A virus infection. Vgamma9Vdelta2 T lymphocytes rapidly upregulate expression of CD25 and CD69 and produce IFN-gamma following influenza infection of PBMC. Moreover, the recognition is cross-reactive between various subtypes of influenza, but not with vaccinia virus. Vgamma9Vdelta2 T cell responses are potently reduced by the HMG-CoA reductase inhibitor mevastatin, which inhibits the mevalonate pathway and IPP synthesis. Our results indicate that influenza virus infection induces the rapid activation and function of Vgamma9Vdelta2 T lymphocytes in the peripheral blood via a mechanism that depends on the mevalonate pathway.

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.

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

Although human and bovine gammadelta T cells were shown to express MHC class II antigen and function as APCs, attempts to determine if mouse gammabeta T cells have similar functions remained unsuccessful. We now show that gammadelta T cells derived from immunized mice also can be induced to express MHC class II and co-stimulatory molecules after activation in vitro, and are capable of antigen presentation. Using highly purified gammadelta T cells, we found that, unlike human gammadelta T cells, the expression of MHC class II molecules by mouse gammadelta T cells is limited to newly activated cells. Highest levels of MHC class II expression were seen on activated gammadelta T cells that had lost most surface-expressed gammadelta TCR while exhibiting increased levels of intracellular gammadelta TCR. In the absence of further stimulation, MHC class II expression gradually declined with the gammadelta T cells regaining their surface TCR. We also show that cytokine-activated gammadelta T cells can also express MHC class II antigen and exercise antigen-presenting activity.

gammadeltaT cell-mediated regulation of chemokine producing macrophages during Listeria monocytogenes infection-induced inflammation

Infection of gammadeltaT cell-deficient (TcRdelta-/-) mice with the intracellular bacterium Listeria monocytogenes (Lm) results in an exacerbated inflammatory response characterized by the accumulation of activated macrophages and necrotic liver lesions. Here we investigated whether changes in chemokine production by Lm-elicited macrophages contribute to this abnormal inflammatory response. In response to Lm infection, activated macrophages accumulate in the primary sites of infection in TcRdelta-/- mice and express high amounts of mRNA encoding the chemokines CCL3 (MIP-1alpha), CCL4 (MIP-1beta), CXCL2 (MIP-2) and CXCL10 (IP-10). In the infected tissues of TcRdelta-/- the number of chemokine-synthesizing macrophages was higher than in wild-type (WT) mice, with the amount of MIP-1alpha and MIP-1beta secreted by individual macrophages in the spleen of TcRdelta-/- mice also being significantly higher than in WT mice. By contrast, protease activity and NO production in individual splenic macrophages of Lm-infected TcRdelta-/- and WT mice were comparable. Pathogen-elicited macrophages in TcRdelta-/- mice also expressed high levels of the CCL3 and CCL4 receptor, CCR5. In macrophage-gammadeltaT cell co-cultures, chemokine-producing macrophages were killed by cytotoxic Vgamma1+ T cells in a Fas-FasL-dependent manner consistent with the high levels of chemokine-producing macrophages seen in infected TcRdelta-/- mice being due to the absence of Vgamma1+ T cells. Together these findings highlight the importance of gammadeltaT cells in regulating macrophage anti-microbial responses.

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.

Importance of murine Vdelta1gammadelta T cells expressing interferon-gamma and interleukin-17A in innate protection against Listeria monocytogenes infection

Murine gammadelta T cells participate in the innate immune response against infection by an intracellular pathogen Listeria monocytogenes. Vdelta1+gammadelta T cells coexpressing Vgamma6 are a major gammadelta T-cell subpopulation induced at an early stage of L. monocytogenes infection in the livers of infected mice. To investigate the protective role of the Vgamma6/Vdelta1+gammadelta T cells against L. monocytogenes infection, Vdelta1 gene-deficient (Vdelta1-/-) mice were analysed because these mice selectively lacked a Vgamma6/Vdelta1+gammadelta T-cell subpopulation in the L. monocytogenes-infected liver. The Vdelta1-/- mice showed increased bacterial burden in the liver and spleen, and decreased survival rate at an early stage of L. monocytogenes infection when compared to wild-type mice. Histological examination showed abscess-like lesions and unorganized distribution of macrophages in the liver of the Vdelta1-/- mice but not in the wild-type mice after L. monocytogenes infection. The Vgamma6/Vdelta1+gammadelta T cells produced interferon-gamma and interleukin-17A. All the results suggest that murine Vgamma6/Vdelta1+gammadelta T cells control the innate protective response against L. monocytogenes infection through production of the proinflammatory cytokines interferon-gamma and interleukin-17A in the infected liver.

Defective tryptophan catabolism underlies inflammation in mouse chronic granulomatous disease

Half a century ago, chronic granulomatous disease (CGD) was first described as a disease fatally affecting the ability of children to survive infections. Various milestone discoveries have since been made, from an insufficient ability of patients' leucocytes to kill microbes to the underlying genetic abnormalities. In this inherited disorder, phagocytes lack NADPH oxidase activity and do not generate reactive oxygen species, most notably superoxide anion, causing recurrent bacterial and fungal infections. Patients with CGD also suffer from chronic inflammatory conditions, most prominently granuloma formation in hollow viscera. The precise mechanisms of the increased microbial pathogenicity have been unclear, and more so the reasons for the exaggerated inflammatory response. Here we show that a superoxide-dependent step in tryptophan metabolism along the kynurenine pathway is blocked in CGD mice with lethal pulmonary aspergillosis, leading to unrestrained Vgamma1(+) gammadelta T-cell reactivity, dominant production of interleukin (IL)-17, defective regulatory T-cell activity and acute inflammatory lung injury. Although beneficial effects are induced by IL-17 neutralization or gammadelta T-cell contraction, complete cure and reversal of the hyperinflammatory phenotype are achieved by replacement therapy with a natural kynurenine distal to the blockade in the pathway. Effective therapy, which includes co-administration of recombinant interferon-gamma (IFN-gamma), restores production of downstream immunoactive metabolites and enables the emergence of regulatory Vgamma4(+) gammadelta and Foxp3(+) alphabeta T cells. Therefore, paradoxically, the lack of reactive oxygen species contributes to the hyperinflammatory phenotype associated with NADPH oxidase deficiencies, through a dysfunctional kynurenine pathway of tryptophan catabolism. Yet, this condition can be reverted by reactivating the pathway downstream of the superoxide-dependent step.

Regulatory T cell populations in sepsis and trauma

Sepsis syndrome remains the leading cause of mortality in intensive care units. It is now believed that along with the body's hyperinflammatory response designated to eliminate the underlying pathogen, mechanisms are initiated to control this initial response, which can become deleterious and result in immune dysfunctions and death. A similar state of immune suppression has been described after numerous forms of severe trauma/injury. Although the evidence for immune dysfunctions after sepsis has grown, much remains to be understood about mechanisms underpinning its development and how it acts to increase the morbid state of the critically ill patient. In this context, although the majority of clinical and basic science conducted so far has focused on the roles of myeloid cell populations, the contribution of T lymphocytes and in particular, of regulatory T cells has been somewhat ignored. The studies presented here support the concept that regulatory T lymphocytes (CD4+CD25+ regulatory, gammadelta, and NK T cells) play a role in the control of immune responses and are affected by injury and sepsis. This may be related to their capacity to interact with components of the innate and adaptive immune responses and to their ability to be activated nonspecifically by bacterial products and/or cytokines and to regulate through direct cell-cell and/or soluble mediators. It is our hope that a better understanding of the mechanism through which those rare lymphocyte subsets exert such a profound effect on the immune response may help in improving our ability not only to diagnose but also to treat the critically ill individual.

Plasmodium berghei XAT: contribution of gammadelta T cells to host defense against infection with blood-stage nonlethal malaria parasite

We examined a potential role of gammadelta T cells in protective immunity to blood-stage Plasmodium berghei XAT infection. Plasmodium berghei XAT is an attenuated variant of the lethal strain P. berghei NK65 and its infection is self-resolving in immune competent mice. To determine whether gammadelta T cells are essential for the resolution of P. berghei XAT malaria, mice were depleted of gammadelta T cells with anti-TCRgammadelta antibody treatment. Although mice that had received control antibody resolved infections, mice received anti-TCRgammadelta antibody could not control their infections and eventually died. Spleen cells from infected mice produced IFN-gamma and nitric oxide (NO) within the first week of infection, however, levels of IFN-gamma and NO in gammadelta T cell-depleted mice were significantly lower than in control mice. To examine whether gammadelta T cells are involved in the antibody production, malarial-specific antibodies of the various isotypes were measured in the sera of gammadelta T cell-depleted mice and control mice. Serum levels of IgG2a, which was known to be a protective antibody in P. berghei XAT malaria, were significantly lower in gammadelta T cell-depleted mice than in control mice, whereas levels of IgG1 were comparable to those in control mice. Our results indicated that the presence of the gammadelta T cell subset was essential for resolution of blood-stage P. berghei XAT malaria and played a modulatory role in the development of Th1 response and host defense against this malarial parasites.

gammadelta T cells condition dendritic cells in vivo for priming pulmonary CD8 T cell responses against Mycobacterium tuberculosis

gammadelta T cells and dendritic cells are quickly recruited to the lungs shortly after intranasal vaccination with BCG, but the functional in vivo interplay between these two cell populations and its role in the induction of adaptive immune responses is unclear. Using TCR-deficient mice and bone marrow chimeras, we show here that gammadelta T cells provide a non-redundant early source of IFN-gamma in vivo, which enhances IL-12 production by lung dendritic cells. The in vivo-conditioned dendritic cells, in turn, prime a more efficient lung CD8 T cell response against Mycobacterium tuberculosis. Thus, strategies exploiting gammadelta T cell function and IFN-gamma production could be valuable for the design and testing of mucosal vaccines.

IL-17 production is dominated by gammadelta T cells rather than CD4 T cells during Mycobacterium tuberculosis infection

IL-17 is a cytokine produced by T cells in response to IL-23. Recent data support a new subset of CD4 Th cells distinct from Th1 or Th2 cells that produce IL-17 and may contribute to inflammation. In this study, we demonstrate that, in naive mice, as well as during Mycobacterium tuberculosis infection, IL-17 production is primarily from gammadelta T cells and other non-CD4(+)CD8(+) cells, rather than CD4 T cells. The production of IL-17 by these cells is stimulated by IL-23 alone, and strongly induced by the cytokines, including IL-23, produced by M. tuberculosis-infected dendritic cells. IL-23 is present in the lungs early in infection and the IL-17-producing cells, such as gammadelta T cells, may represent a central innate protective response to pulmonary infection.

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.

Identification of novel gammadelta T-cell subsets following bacterial infection in the absence of Vgamma1+ T cells: homeostatic control of gammadelta T-cell responses to pathogen infection by Vgamma1+ T cells

Although gammadelta T cells are a common feature of many pathogen-induced immune responses, the factors that influence, promote, or regulate the response of individual gammadelta T-cell subsets to infection is unknown. Here we show that in the absence of Vgamma1+ T cells, novel subsets of gammadelta T cells, expressing T-cell receptor (TCR)-Vgamma chains that normally define TCRgammadelta+ dendritic epidermal T cells (DETCs) (Vgamma5+), intestinal intraepithelial lymphocytes (iIELs) (Vgamma7+), and lymphocytes associated with the vaginal epithelia (Vgamma6+), are recruited to the spleen in response to bacterial infection in TCR-Vgamma1-/- mice. By comparison of phenotype and structure of TCR-Vgamma chains and/or -Vdelta chains expressed by these novel subsets with those of their epithelium-associated counterparts, the Vgamma6+ T cells elicited in infected Vgamma1-/- mice were shown to be identical to those found in the reproductive tract, from where they are presumably recruited in the absence of Vgamma1+ T cells. By contrast, Vgamma5+ and Vgamma7+ T cells found in infected Vgamma1-/- mice were distinct from Vgamma5+ DETCs and Vgamma7+ iIELs. Functional analyses of the novel gammadelta T-cell subsets identified for infected Vgamma1-/- mice showed that whereas the Vgamma5+ and Vgamma7+ subsets may compensate for the absence of Vgamma1+ T cells by producing similar cytokines, they do not possess cytocidal activity and they cannot replace the macrophage homeostasis function of Vgamma1+ T cells. Collectively, these findings identify novel subsets of gammadelta T cells, the recruitment and activity of which is under the control of Vgamma1+ T cells.