Sequential appearance of gamma/delta- and alpha/beta-bearing T cells in the peritoneal cavity during an i.p. infection with Listeria monocytogenes

γδ T Cells Participating in Nervous Systems: A Story of Jekyll and Hyde

γδ T cells are distributed in various lymphoid and nonlymphoid tissues, and act as early responders in many conditions. Previous studies have proven their significant roles in infection, cancer, autoimmune diseases and tissue maintenance. Recently, accumulating researches have highlighted the crosstalk between γδ T cells and nervous systems. In these reports, γδ T cells maintain some physiological functions of central nervous system by secreting interleukin (IL) 17, and neurons like nociceptors can in turn regulate the activity of γδ T cells. Moreover, γδ T cells are involved in neuroinflammation such as stroke and multiple sclerosis. This review illustrates the relationship between γδ T cells and nervous systems in physiological and pathological conditions.

Tissue Adaptations of Memory and Tissue-Resident Gamma Delta T Cells

Epithelial and mucosal barriers are critical interfaces physically separating the body from the outside environment and are the tissues most exposed to microorganisms and potential inflammatory agents. The integrity of these tissues requires fine tuning of the local immune system to enable the efficient elimination of invasive pathogens while simultaneously preserving a beneficial relationship with commensal organisms and preventing autoimmunity. Although they only represent a small fraction of circulating and lymphoid T cells, γδ T cells form a substantial population at barrier sites and even outnumber conventional αβ T cells in some tissues. After their egress from the thymus, several γδ T cell subsets naturally establish residency in predetermined mucosal and epithelial locations, as exemplified by the restricted location of murine Vγ5⁺ and Vγ3Vδ1⁺ T cell subsets to the intestinal epithelium and epidermis, respectively. Because of their preferential location in barrier sites, γδ T cells are often directly or indirectly influenced by the microbiota or the pathogens that invade these sites. More recently, a growing body of studies have shown that γδ T cells form long-lived memory populations upon local inflammation or bacterial infection, some of which permanently populate the affected tissues after pathogen clearance or resolution of inflammation. Natural and induced resident γδ T cells have been implicated in many beneficial processes such as tissue homeostasis and pathogen control, but their presence may also exacerbate local inflammation under certain circumstances. Further understanding of the biology and role of these unconventional resident T cells in homeostasis and disease may shed light on potentially novel vaccines and therapies.

CD5-NK1.1+ γδ T Cells that Develop in a Bcl11b-Independent Manner Participate in Early Protection against Infection

We recently found that a unique subset of innate-like γδ T cells develops from the DN2a stage of the fetal thymus independently of the zinc-finger transcription factor B cell leukemia/lymphoma 11b (Bcl11b). Herein, we characterize these Bcl11b-independent γδ T cells in the periphery as CD5^-NK1.1⁺ and Granzyme B⁺, and we show that they are capable of producing interferon (IFN)-γ upon T cell receptor stimulation without Ca²⁺ influx. In wild-type mice, these cells were sparse in lymphoid tissues but abundant in non-lymphoid tissues, such as the liver. Bcl11b-independent CD5^-NK1.1⁺ γδ T cells appeared and contributed to early protection before Bcl11b-dependent CD5⁺NK1.1^- γδ T cells following Listeria monocytogenes infection, resembling their sequential appearance during development in the thymus.

Mitogenicity of bacterial lipopolysaccharide on the T lymphocyte population bearing the γδT cell receptor

In vitro [3H]-thymidine (TdR) uptake in T lymphocyte populations, taken and purified from proteose peptone-induced peritoneal exudate cells (PEC), spleens and thymuses of C3H/HeN mice, were investigated by stimulation with bacterial lipopolysaccharide (LPS). The T cells taken from PEC (PEC-T) were purified by passing them through a nylon fiber column (Nfc) and a G-10 column. They were then treated with anti-lak, anti-Mac-1 and anti-LR-1 antibodies plus complement (C). The PEC-T cells showed an increased [ 3H]-TdR uptake in response to LPS, while the splenic T cells and thymic T cells that had been purified and treated by a similar procedure with minor modifications, poorly responded to LPS and did not respond to LPS, respectively. The response of PEC-T to LPS was abolished when the PEC-T were pretreated with anti-Thy-1 or anti-γδ antibody plus C, but not αβ, T cell receptor (TCR) antibody plus C. The thymic T cells did not show any increase of [ H]-TdR uptake in response to LPS or anti-αβ or γδTCR antibody. However, obvious uptake did occur when the cells were stimulated with LPS and anti-γδTCR antibody, but not with anti-αβTCR antibody. IL-1 did not substitute for LPS in the response. These results suggest that LPS has a mitogenic ability to respond to a T cell population bearing γδTCR in PEC, and to a γδTCR-stimulated cell population in thymic cells. The difference in response to LPS between PEC-γδT and thymic γδT cells was discussed.

CD30L/CD30 is critical for maintenance of IL-17A-producing γδ T cells bearing Vγ6 in mucosa-associated tissues in mice

CD30 ligand (CD30L, CD153), a member of the tumor necrosis factor (TNF) superfamily, and its receptor CD30 are important for differentiation and activation of CD4(+) T helper type 17 (Th17) cells. In this report, we demonstrate that the interleukin 17A (IL-17A)-producing γδ T cells normally developed in the fetal thymus, whereas Vγ1(-)Vγ4(-) γδ T cells expressed Vγ6/Vδ1 gene transcript selectively decreased in mucosa-associated tissues in naive CD30KO or CD30LKO mice. Moreover, CD30 and CD30L were expressed preferentially by Vγ1(-)Vγ4(-) γδ T cells in naive mice. The bacteria clearance was attenuated by the impaired response of the IL-17A-producing γδ T cells and decreased infiltration of neutrophils in CD30KO or CD30LKO mice. In vivo administration of agonistic anti-CD30 monoclonal antibody restored the ability of protection against Listeria monocytogenes by enhancing Vγ1(-)Vγ4(-) γδ T cells producing IL-17A not only in wild-type but also CD30LKO mice. Taken together, it appears that CD30L/CD30 signaling plays an important role in the maintenance and activation of IL-17A-producing γδ T cells presumably bearing Vγ6 in the mucosa-associated tissues of mice.

Gammadelta T cells: innately adaptive immune cells?

T cells employ a cell surface heterodimeric molecule, the T cell receptor (TCR), to recognize specific antigens (Ags) presented by major histocompatibility complex (MHC) molecules and carry out adaptive immune responses. Most T cells possess a TCR with an α and a β chain. However, a TCR constituted by a γ and a δ chain has been described, defining a novel subset of T cells. γδ TCRs specific for a wide variety of ligands, including bacterial phosphoantigens, nonclassical MHC-I molecules and unprocessed proteins, have been found, greatly expanding the horizons of T cell immune recognition. This review aims to provide background in γδ T cell history and function in mouse and man, as well as to provide a critical view of some of the latest developments on this still enigmatic class of immune cells.

IL-23 receptor regulates unconventional IL-17-producing T cells that control bacterial infections

IL-23 plays an important role in autoimmune tissue inflammation and induces the generation of not fully characterized effector cells that mediate protection against pathogens. In this paper, we established the essential role of IL-23R in the host response against intracellular pathogens. IL-23 was critical for the expansion or maintenance of gammadelta and double negative (DN) alphabeta T cells. These cells were rapidly recruited to the site of infection and produced large amounts of IL-17, IFN-gamma, and TNF-alpha. Notably, DN T cells transferred into L. monocytogenes-infected RAG2(-/-) mice prevented bacterial growth, confirming their protective role against intracellular pathogens. Our results show that IL-23 regulates the function of IL-17-producing gammadelta and DN T cells, two essential components of the early protective immune response directed against intracellular pathogens.

Identification of CD25+ gamma delta T cells as fetal thymus-derived naturally occurring IL-17 producers

We previously reported that resident gammadelta T cells in the peritoneal cavity rapidly produced IL-17 in response to Escherichia coli infection to mobilize neutrophils. We found in this study that the IL-17-producing gammadelta T cells did not produce IFN-gamma or IL-4, similar to Th17 cells. IL-17-producing gammadelta T cells specifically express CD25 but not CD122, whereas CD122(+) gammadelta T cells produced IFN-gamma. IL-17-producing gammadelta T cells were decreased but still present in IL-2- or CD25-deficient mice, suggesting a role of IL-2 for their maintenance. IFN-gamma-producing CD122(+) gammadelta T cells were selectively decreased in IL-15-deficient mice. Surprisingly, IL-17-producing gammadelta T cells were already detected in the thymus, although CD25 was not expressed on the intrathymic IL-17-producing gammadelta T cells. The number of thymic IL-17-producing gammadelta T cells was peaked at perinatal period and decreased thereafter, coincided with the developmental kinetics of Vgamma6(+) Vdelta1(+) gammadelta T cells. The number of IL-17-producing gammadelta T cells was decreased in fetal thymus of Vdelta1-deficient mice, whereas Vgamma5(+) fetal thymocytes in normal mice did not produce IL-17. Thus, it was revealed that the fetal thymus-derived Vgamma6(+) Vdelta1(+) T cells functionally differentiate to produce IL-17 within thymus and thereafter express CD25 to be maintained in the periphery.

A. Deficiency of gammadelta T lymphocytes contributes to mortality and immunosuppression in sepsis

Studies have indicated that gammadelta T lymphocytes play an important role in the regulation of immune function and the clearance of intracellular pathogens. We have recently reported that intraepithelial lymphocytes (IEL), which are rich in gammadelta T cells, within the small intestine illustrated a significant increase in apoptosis and immune dysfunction in mice subjected to sepsis. However, the contribution of gammadelta T cells to the host response to polymicrobial sepsis remains unclear. In this study, we initially observed that after sepsis induced by cecal ligation and puncture (CLP), there was an increase in small intestinal IEL CD8+gammadelta+ T cells in control gammadelta+/+ mice. Importantly, we subsequently found an increased early mortality in mice lacking gammadelta T cells (gammadelta-/- mice) after sepsis. This was associated with decreases in plasma TNF-alpha, IL-6, and IL-12 levels in gammadelta-/- mice compared with gammadelta+/+ mice after sepsis. In addition, even though in vitro LPS-stimulated peritoneal macrophages showed a reduction in IL-6 and IL-12 release after CLP, these cytokines were less suppressed in macrophages isolated from gammadelta-/- mice. Alternatively, IL-10 release was not different between septic gammadelta+/+ and gammadelta-/- mice. Whereas T helper (Th)1 cytokine release by anti-CD3-stimulated splenocytes was significantly depressed in septic gammadelta+/+ mice, there was no such depression in gammadelta-/- mice. However, gammadelta T cell deficiency had no effect on Th2 cytokine release. These findings suggest that gammadelta T cells may play a critical role in regulating the host immune response and survival to sepsis, in part by alteration of the level of IEL CD8+gammadelta+ T cells and through the development of the Th1 response.

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.

Membrane HSP70: the molecule triggering gammadelta T cells in the early stage of tumorigenesis

Many studies support the supposition that HSPs expressed on the cell membrane play an important role in cancer immunity. In the present study, we demonstrated that HSP60 and HSP70 are markedly increased on the cell membrane of human Epstein-Barr virus (EBV) transformed B cells. In order to investigate whether these molecules were involved in the response of human gammasigma T cells to transformed cells, the cytotoxicities of gammasigma T cells to transformed cells with or without an HSP60/70 gene knockdown were evaluated. gammasigma T cells showed marked cytotoxities to transformed cells. Down-regulation of HSP70 expression could inhibit the reactions, whereas down-regulation of HSP60 expression had little such effect. Moreover, HSP72 could significantly induce human gammasigma T cells to proliferate in vitro. Taken together, our data indicated that HSP60 and HSP70 could be valuable biomarkers for the prediction of early stage in tumorigenesis. Additionally, HSP72 might be a potential candidate of the adjuvant for gammasigma T cells in tumor immunotherapy.

Delineation of the function of a major gamma delta T cell subset during infection

Gammadelta T cells play important but poorly defined roles in pathogen-induced immune responses and in preventing chronic inflammation and pathology. A major obstacle to defining their function is establishing the degree of functional redundancy and heterogeneity among gammadelta T cells. Using mice deficient in Vgamma1+ T cells which are a major component of the gammadelta T cell response to microbial infection, a specific immunoregulatory role for Vgamma1+ T cells in macrophage and gammadelta T cell homeostasis during infection has been established. By contrast, Vgamma1+ T cells play no significant role in pathogen containment or eradication and cannot protect mice from immune-mediated pathology. Pathogen-elicited Vgamma1+ T cells also display different functional characteristics at different stages of the host response to infection that involves unique and different populations of Vgamma1+ T cells. These findings, therefore, identify distinct and nonoverlapping roles for gammadelta T cell subsets in infection and establish the complexity and adaptability of a single population of gammadelta T cells in the host response to infection that is not predetermined, but is, instead, shaped by environmental factors.

Vdelta1+ gammadelta T cells producing CC chemokines may bridge a gap between neutrophils and macrophages in innate immunity during Escherichia coli infection in mice

An influx of neutrophils followed a short time later by an influx of macrophages to the infected site plays a key role in innate immunity against Escherichia coli infection. We found in this study that Vdelta1-/- mice exhibited impaired accumulation of peritoneal macrophages but not neutrophils and delayed bacterial clearance after i.p. inoculation with E. coli. Peritoneal gammadelta T cells from E. coli-infected wild-type mice produced CCL3/MIP-1alpha and CCL5/RANTES in response to gammadelta TCR triggering in vitro, whereas such production was not evident in gammadelta T cells from E. coli-infected Vdelta1-/- mice. Neutralization of CCL3/MIP-1alpha by a specific mAb in vivo significantly inhibited the accumulation of macrophages in the peritoneal cavity after E. coli infection, resulting in exacerbated bacterial growth in the peritoneal cavity. These results suggest that Vdelta1+ gammadelta T cells bridge a gap between neutrophils and macrophages in innate immunity during E. coli infection mediated by production of CC chemokines, enhancing macrophage trafficking to the site of infection.

Infiltration of T-lymphocytes in the brain after anterior chamber inoculation of a neurovirulent and neuroinvasive strain of HSV-1

Following anterior chamber (AC) inoculation of BALB/c mice with the KOS strain of herpes simplex virus type 1 (HSV-1), or with H129, a neuroinvasive and neurovirulent strain of HSV-1, both strains of virus spread from the injected eye through the brain to cause retinitis. However, KOS-infected mice develop retinitis in the uninoculated eye only, whereas H129-infected mice develop bilateral retinitis. Previous studies have shown that infiltrating T-cells in the suprachiasmatic nuclei (SCN) of the hypothalamus of KOS-infected mice concomitant with or before virus protect KOS-infected mice from ipsilateral retinitis. To determine the timing of T cell infiltration and cytokine production in the brain of H129-infected mice, adjacent, frozen sections of the brain were immunostained for virus, T-cells, IL-2, TNF-alpha or IFN-gamma. T-cells infiltrated the brains of H129-infected mice and cytokines were produced in infected tissues. However, virus spread to the optic nerve and retina of both the inoculated and uninoculated eye before T-cells and cytokines were detected in the SCN of H129-infected mice. These results suggest that infiltrating T-cells in the SCN of H129-infected mice may arrive too late to prevent the spread of virus into the optic nerves and retinas and thus prevent development of bilateral retinitis in infected mice.

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

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

Human gamma delta T cells induce dendritic cell maturation

gamma delta T cells are known to be involved in the innate immune defenses against infectious microorganisms. Herein, we considered that gamma delta T cells could also influence adaptative immunity by interacting with dendritic cells (DC) in the early phase of the immune response. To investigate this hypothesis, gamma delta T cells isolated from the peripheral blood of healthy volunteers were cocultured with autologous monocyte-derived dendritic cells, which were subsequently analyzed for their expression of key surface molecules and for their production of IL-12. First, we found that gamma delta T cells induced the upregulation of HLA-DR, CD86, and CD83 on DC. This effect did not require cell to cell contact and could be blocked by a neutralizing anti-TNF antibody. We then observed that gamma delta T cells activated by the synthetic phosphoantigen bromohydrin pyrophosphate (BrHPP) induced the production of IL-12 (p40) and IL-12 (p70) by DC, an effect that involved IFN-gamma production. The relevance of this finding to DC function was demonstrated by the increased production of IFN-gamma by alloreactive T cells when stimulated in a mixed leucocyte reaction with DC preincubated with activated gamma delta T cells. We conclude that gamma delta T cell activation might result in DC maturation and thereby in enhanced alpha beta T cell responses.

Correlation between the numbers of gammadelta T cells and CD4+ HLA-DR+ T cells in broncho-alveolar lavage fluid from patients with diffuse lung disease

CD4+ HLA-DR+ T cells are known to be increasing in broncho-alveolar lavage fluid (BALF) from patients with sarcoidosis, and related to disease activity. Although there are several reports that the number of gammadelta T cells in peripheral blood from patients with sarcoidosis are increasing, contradictory assertions can be seen about the number of gammadelta T cells in BALF, and the clinical significance on the presence of gammadelta T cells in disease site of patients with diffuse lung disease including sarcoidosis. The absolute number of gammadelta T cells and CD4+ HLA-DR+ T cells in BALF were determined by flow cytometry in 107 patients with diffuse lung diseases; 56 with sarcoidosis, 36 with collagen vascular diseases with lung involvement and 15 with idiopathic pulmonary fibrosis. We also measured the number of the transferrin receptor-positive macrophages in BALF. The correlation between gammadelta T cells and activated (maybe antigen-specific) T cells and macrophages were evaluated. Sarcoidosis patients were also evaluated from the data of the number of gammadelta T cells in peripheral blood by flow cytometry and clinical backgrounds. A significant correlation between the numbers of these two cell types was detected in each of the three patient groups. The percentage of peripheral gammadelta T cells was markedly increased in 7 sarcoidosis patients, each of whom also showed affected organs other than lung, however, 5 individuals did not show an increased number of gammadelta T cells in BALF. The number of gammadelta T cells in BALF did not correlate with the number of transferrin receptor-positive macrophages in all three patient groups. These results suggest that the increased number of gammadelta T cells in diffuse lung diseases likely plays a role in immunosurveillance and contributes to the activation of antigen-specific alphabeta T cell.

Nitric oxide production and iNOS mRNA expression in mice induced by repeated stimulation with live Fusobacterium nucleatum

There have been few studies on the detection of direct nitric oxide (NO) production and interferon-gamma (IFN-gamma) in vivo without using animal cell culture. We questioned whether NO and IFN-gamma could be produced at the site of infection. The peritoneal cavity of mice was used as the local infection model. NO and IFN-gamma in abdominal washings from these mice were measured directly at various times after injection of Fusobacterium nucleatum, a gram-negative rod periodontal pathogen. The mice were divided into three groups: those treated with live bacteria (LB), those treated with heat-killed bacteria (HKB) and those untreated: normal (N). These mice were compared on the basis of cell filtration, NO and IFN-gamma production by injection of live bacteria (LFn) or heat-killed bacteria (HKFn). In the LB group, the total cell number increased corresponding to an increase in neutrophils after injection of both LFn and HKFn. A low level of NO was constantly produced in abdominal washings, but a significant amount of NO was synthesized in the LB group only 12 hr to 24 hr after injection of LFn. At the same time iNOS enzyme activity and iNOS mRNA expression were detected. IFN-gamma, which may contribute to enhance NO production, was also secreted at a high level from peritoneal exudate cells (PEC) at 12 hr and 24 hr in the LB group by stimulation of LFn. At 12 hr and 24 hr, iNOS positive cells in the LB group by infection of LFn were identified and shown to contain mostly macrophages. These findings indicate that live bacteria play important roles in NO production by macrophages. It is suggested that NO may contribute to the inflammatory response during F. nucleatum infection in periodontitis.

Intraperitoneal immune cell responses to Eubacterium saphenum in mice

Oral asaccharolytic Eubacterium saphenum, which are newly isolated gram-positive rods and one of the predominant microorganisms in human periodontal pockets, were injected intraperitoneally in mice to elucidate their pathogenicity in periodontal diseases. Infiltrating immune cells in the peritoneal exudate were quantitated and intracellular T cell (CD4+/CD8+/gammadelta+) production of cytokines IL-4 and IFN-gamma which are related to cellular and humoral immunity, respectively, was determined. Neutrophils appeared first in peritoneal exudates, followed by macrophages and lymphocytes, after the injection of either E. saphenum or Porphyromonas gingivalis. Intracellular IL-4+ and IFN-gamma+ gammadelta T cells were detected in the exudates after the injection of E. saphenum (4.6 +/- 0.8% and 10.1 +/- 1.4%, respectively) and P. gingivalis (5.3 +/- 1.6% and 10.1 +/- 2.1%, respectively). The intracellular production of IL-4/IFN-gamma in CD4+/CD8+ T cells was rather low indicating that the main response was from gammadelta T cells which initiated the immune reactions in mouse peritoneal cavities after injection of E. saphenum or P. gingivalis. Serum IgG and IgM levels were elevated in animals injected with E. saphenum and similarly with P. gingivalis. The present study showed that with slight differences, similar modes of cell response and cytokine and Ig production were observed after intraperitoneal injection of both E. saphenum and P. gingivalis, indicating that E. saphenum may play just as important a role in periodontal diseases as P. gingivalis.

A protective role of interleukin-15 in a mouse model for systemic infection with herpes simplex virus

To define the role of cytokine binding to the IL-2/IL-15R beta chain in protective immunity against systemic infection with herpes simplex virus type 2 (HSV-2), IL-2/IL-15 receptor(R)beta knock-out mice were inoculated intraperitoneally with HSV-2 strain 186. IL-2/IL-15R beta-deficient mice were susceptible to systemic HSV-2 infection compared with their heterozygous littermates. The emergence of natural killer (NK) cells was impaired in IL-2/IL-15R beta knock-out mice, but CD4(+) T cell receptor (TCR) alpha beta(+) T cells were normally detected in the peritoneal cavity after infection with HSV-2. However, the generation of HSV-2-specific CD4(+) T helper (Th) 1 cells producing interferon-gamma was impaired in IL-2/IL-15R beta knock-out mice following HSV-2 infection. The serum IL-15 level in control mice was increased in the early stage after HSV-2 infection but was not detectable in IL-2/IL-15R beta knock-out mice. In vivo administration of recombinant IL-15 protected normal mice from HSV-2-induced lethality, accompanied by increases in numbers of NK cells and HSV-2-specific Th1 cells. Taken together, these results suggest that IL-15, using the IL-2/IL15R beta chain, plays an important role in mounting protective immunity during the course of systemic HSV-2 infection.

Reduced formation of granulomata in gamma(delta) T cell knockout BALB/c mice inoculated with Mycobacterium avium subsp. paratuberculosis

The role of gamma(delta) T cells in the bovine immune response to Mycobacterium avium subsp. paratuberculosis (M. paratuberculosis) infection is poorly understood. Accordingly, using BALB/c mice that are innately susceptible to M. paratuberculosis, we compared wild-type and gamma(delta) T cell knockout BALB/c mice to study the protective roles of gamma(delta) T cells in M. paratuberculosis infection. Ten-week-old mice were inoculated intraperitoneally with either a low dose (4 x 10(6) colony-forming units [CFU]/mouse) or a high dose (4 x 10(9) CFU/mouse) of M. paratuberculosis strain ATCC 19698. Histopathologic and morphometric examinations showed reductions in the number and area of granulomatous lesions in the liver of the knockout mice at 18 weeks after inoculation with either the low or the high dose of the mycobacteria. Furthermore, at 18 weeks after inoculation, the bacterial load in the spleens of the knockout mice inoculated with the high dose was significantly lower than that of wild-type mice. No differences were found in bacterial load between the knockout and the wild-type mice in the low-dose groups. In contrast, in the livers of wild-type mice inoculated with either the low or high mycobacterial dose, increased areas of epithelioid granulomata were observed and the granulomata became disseminated widely during the experimental period. These findings in model mice suggest that gamma(delta) T cells, rather than restricting mycobacterial growth, may play a crucial role in development of epithelioid granulomata similar to those seen consistently in bovine paratuberculosis. The results of this study may have relevance to our understanding of the pathogenesis of paratuberculosis in ruminants, in which a prominent number of gamma(delta) T cells exist in the lymphoid system.

[gamma][delta] cells: a right time and a right place for a conserved third way of protection

The tripartite subdivision of lymphocytes into B cells, alphabeta T cells, and gammadelta cells has been conserved seemingly since the emergence of jawed vertebrates, more than 450 million years ago. Yet, while we understand much about B cells and alphabeta T cells, we lack a compelling explanation for the evolutionary conservation of gammadelta cells. Such an explanation may soon be forthcoming as advances in unraveling the biochemistry of gammadelta cell interactions are reconciled with the abnormal phenotypes of gammadelta-deficient mice and with the striking differences in gammadelta cell activities in different strains and species. In this review, the properties of gammadelta cells form a basis for understanding gammadelta cell interactions with antigens and other cells that in turn form a basis for understanding immunoprotective and regulatory functions of gammadelta cells in vivo. We conclude by considering which gammadelta cell functions may be most critical.

Downmodulation of the inflammatory response to bacterial infection by gammadelta T cells cytotoxic for activated macrophages

Although gammadelta T cells are involved in the regulation of inflammation after infection, their precise function is not known. Intraperitoneal infection of T cell receptor (TCR)-delta(-/-) mice with the intracellular bacterium Listeria monocytogenes resulted in the development of necrotic foci in the livers. In contrast, the peritoneal cavities of infected TCR-delta(-/-) mice contained an accumulation of low density activated macrophages and a reduced percentage of macrophages undergoing apoptosis. gammadelta T cell hybridomas derived from mice infected with Listeria were preferentially stimulated by low density macrophages from peritoneal exudates of infected mice. Furthermore, primary splenic gammadelta T cells isolated from Listeria-infected mice were cytotoxic for low density macrophages in vitro, and cytotoxicity was inhibited in the presence of antibodies to the gammadelta TCR. These results demonstrate a novel interaction between gammadelta T cells and activated macrophages in which gammadelta T cells are stimulated by terminally differentiated macrophages to acquire cytotoxic activity and which, in turn, induce macrophage cell death. This interaction suggests that gammadelta T cells regulate the inflammatory response to infection with intracellular pathogens by eliminating activated macrophages at the termination of the response.

gammadelta T cells may dichotomously modulate infection with avirulent Salmonella choleraesuis via IFN-gamma and IL-13 in mice

To investigate the roles of gammadelta T cells in Salmonella infection, we examined the resolution of an intraperitoneal infection with avirulent Salmonella choleraesuis 31N-1 in mice lacking T-cell-receptor (TCR) alphabeta T cells by disruption of the TCRbeta chain gene (TCRbeta(-/-)). The bacteria in TCRbeta(-/-) mice decreased with kinetics similar to that seen in control mice (TCRbeta(+/+)) after infection. The number of natural killer (NK) cells in the peritoneal cavity increased on day 6 after infection and thereafter decreased in both TCRbeta(-/-) and TCRbeta(+/+) mice, whereas the number of gammadelta T cells, in place of alphabeta T cells, increased remarkably in the peritoneal cavity of TCRbeta(-/-) mice on day 6 after infection. The NK cells from Salmonella-infected TCRbeta(-/-) mice produced interferon-gamma (IFN-gamma) but neither interleukin-4 (IL-4) nor IL-13 in response to immobilized anti-NK1.1 monoclonal antibody (mAb). The gammadelta T cells produced IFN-gamma but neither IL-4 nor IL-13 in response to heat-killed Salmonella, whereas both IFN-gamma and IL-13 but no IL-4 was produced by the gammadelta T cells stimulated with immobilized anti-TCRgammadelta mAb. In vivo administration of anti-NK1.1 mAb inhibited the reduction of Salmonella, whereas anti-TCRgammadelta mAb treatment did not affect the bacterial growth in TCRbeta(-/-) mice after Salmonella infection. However, neutralization of endogenous IL-13 with anti-IL-13 mAb enhanced the bacterial clearance in TCRbeta(-/-) mice after infection. These results suggest that NK1.1(+) cells serve mainly to protect against avirulent Salmonella infection in the absence of alphabeta T cells, whereas gammadelta T cells may play dichotomous roles in Salmonella infection through IFN-gamma and IL-13 in TCRbeta(-/-) mice.

gammadelta T cells are a component of early immunity against preerythrocytic malaria parasites

We tested the hypothesis that gammadelta T cells are a component of an early immune response directed against preerythrocytic malaria parasites that are required for the induction of an effector alphabeta T-cell immune response generated by irradiated-sporozoite (irr-spz) immunization. gammadelta T-cell-deficient (TCRdelta(-/-)) mice on a C57BL/6 background were challenged with Plasmodium yoelii (17XNL strain) sporozoites, and then liver parasite burden was measured at 42 h postchallenge. Liver parasite burden was measured by quantification of parasite-specific 18S rRNA in total liver RNA by quantitative-competitive reverse transcription-PCR and by an automated 5' exonuclease PCR. Sporozoite-challenged TCRdelta(-/-) mice showed a significant (P < 0.01) increase in liver parasite burden compared to similarly challenged immunocompetent mice. In support of this result, TCRdelta(-/-) mice were also found to be more susceptible than immunocompetent mice to a sporozoite challenge when blood-stage parasitemia was used as a readout. A greater percentage of TCRdelta(-/-) mice than of immunocompetent mice progressed to a blood-stage infection when challenged with five or fewer sporozoites (odds ratio = 2.35, P = 0.06). TCRdelta(-/-) mice receiving a single irr-spz immunization showed percent inhibition of liver parasites comparable to that of immunized immunocompetent mice following a sporozoite challenge. These data support the hypothesis that gammadelta T cells are a component of early immunity directed against malaria preerythrocytic parasites and suggest that gammadelta T cells are not required for the induction of an effector alphabeta T-cell immune response generated by irr-spz immunization.

Increased absolute number but not proportion of gamma/delta T-lymphocytes in the bronchoalveolar lavage fluid of patients with active pulmonary tuberculosis

SETTING

The proportions and absolute cell count of gamma/delta T-lymphocytes in the peripheral blood of patients with pulmonary tuberculosis (PTB) remains controversial. Since PTB is an infections airway disease, bronchoalveolar T-lymphocytes should be a better indicator of local immune T-cell reaction after TB infection than peripheral blood T-lymphocytes.

OBJECTIVE

To quantitate the absolute cell count and proportions of gamma/delta T-lymphocytes in the bronchoalveolar lavage fluid (BALF) of patients with active PTB.

DESIGN

Bronchoalveolar lavage (BAL) and analysis of lymphocytes in the BALF was performed in 25 patients with active PTB and 16 normal controls. All of the patients were negative for HIV infection and none was immunocompromised. BALF and blood were prepared for cell differential count and flow cytometry analysis using monoclonal antibodies CD3, CD4, CD8, CD25, HLA-DR and gamma/delta as well as alpha/beta T-lymphocyte receptors.

RESULTS

The number of cells per volume of recovered BALF was significantly higher in the patients with active PTB than in normal controls. BALF from active PTB patients also showed increased percentage of lymphocytes and neutrophils. The absolute number of total lymphocytes, CD3+ lymphocytes and CD3+ gamma/delta T-lymphocytes were significantly higher in the BALF, but not in the blood, of patients with TB, however, the proportions of CD3+ gamma/delta T-lymphocytes in BALF of patients with TB was comparable to that of normal controls. gamma/delta T-lymphocytes in the BALF rarely expressed CD4, CD25, and HLA-DR in both groups.

CONCLUSION

These results suggest that gamma/delta T-lymphocytes are not the major subpopulation of CD3+ lymphocytes in the BALF that react to mycobacterial infection in the patients with clinically established active TB.

Experimental autoimmune encephalomyelitis on the SJL mouse: effect of gamma delta T cell depletion on chemokine and chemokine receptor expression in the central nervous system

Experimental autoimmune encephalomyelitis (EAE) is a demyelinating disease of the central nervous system (CNS) that is a model for multiple sclerosis. Previously, we showed that depletion of gamma delta T cells significantly reduced clinical and pathological signs of disease, which was associated with reduced expression of IL-1 beta, IL-6, TNF-alpha, and lymphotoxin at disease onset and a more persistent reduction in IFN-gamma. In this study, we analyzed the effect of gamma delta T cell depletion on chemokine and chemokine receptor expression. In the CNS of control EAE mice, mRNAs for RANTES, eotaxin, macrophage-inflammatory protein (MIP)-1 alpha, MIP-1 beta, MIP-2, inducible protein-10, and monocyte chemoattractant protein-1 were detected at disease onset, increased as disease progressed, and fell as clinical signs improved. In gamma delta T cell-depleted animals, all of the chemokine mRNAs were reduced at disease onset; but at the height of disease, expression was variable and showed no differences from control animals. mRNA levels then fell in parallel with control EAE mice. ELISA data confirmed reduced expression of MIP-1 alpha and monocyte chemoattractant protein-1 at disease onset in gamma delta T cell-depleted mice, and total T cell numbers were also reduced. In normal CNS mRNAs for CCR1, CCR3, and CCR5 were observed, and these were elevated in EAE animals. mRNAs for CCR2 were also detected in the CNS of affected mice. Depletion of gamma delta T cells reduced expression of CCR1 and CCR5 at disease onset only. We conclude that gamma delta T cells contribute to the development of EAE by promoting an inflammatory environment that serves to accelerate the inflammatory process in the CNS.

Escherichia coli infection induces only fetal thymus-derived gamma delta T cells at the infected site

Intraperitoneal infection of mice with Escherichia coli induced activated TCR gamma delta T cells in the peritoneal cavity. We provide evidence that the E. coli-induced gamma delta T cells are derived only from the fetal thymus on the following grounds. The gamma delta T cells were not induced in athymic nude mice and irradiated bone marrow-transferred mice which lack fetal thymus-derived T cells. However, E. coli infection of fetal thymus-grafted nude mice did induce fetal thymus-derived gamma delta T cells. These results suggest that the fetal thymus-derived gamma delta T cells colonize the periphery during early ontogeny, and are maintained until adult age. The E. coli-induced gamma delta T cells express only the Vdelta1 gene. Vgamma6 was predominantly expressed whereas anti-Vgamma1 and anti-Vgamma4 monoclonal antibodies stained less than 3 % of the cells. Direct sequencing of PCR products revealed that Vgamma6 and Vdelta1 genes expressed by the E. coli-induced gamma delta T cells were invariant sequences identical to those expressed in the fetal thymus. The antigen (Ag) specificity of a T cell hybridoma expressing the fetal type Vgamma6 / Vdelta1(+) TCR could not be identified as the cells failed to respond to lipopolysaccharide, E. coli Ag, mycobacterial heat shock protein 65, or isopentenyl pyrophosphate. These results suggest that the Vgamma6 / Vdelta1(+) gamma delta T cells derived from fetal thymus can participate in immune responses against bacterial infection through recognition of a novel class of Ag which is not yet identified.

Beta-estradiol-induced decrease in IL-12 and TNF-alpha expression suppresses macrophage functions in the course of Listeria monocytogenes infection in mice

Mice treated with a contraceptive dose of beta-estradiol (E2) demonstrated changes in their macrophage (Mphi) number and functions. While E2 increased and decreased the Mphi number in PBMC and PEC respectively, it enhanced the in vitro phagocytosis of FITC-labeled beads by both cells. E2 treatment also enhanced the phagocytic function of Mphi as assessed by the in vivo carbon clearance assay. In contrast, the in vitro intracellular killing function of adherent cells in peritoneal exudate cells (PEC) against Listeria monocytogenes decreased after E2 treatment. In line with the decrease in the intracellular killing function, the E2-treated mice showed an impaired protection against L. monocytogenes infection. To clarify the mechanism of the E2-mediated suppression of the protective response against L. monocytogenes infection, we next analyzed the cytokine expression by PEC in E2-treated L. monocytogenes-infected mice. On day 5 of the infection, the expression of IL-12, TNF-alpha and IL-10 by adherent PEC from the E2-treated mice was lower than that from the control-infected mice. The decrease in the cytokine expression by adherent PEC of E2-treated mice coincided with the decrease of IFN-gamma expression, and the increase in the IL-4, IL-10 and TGF-beta expressions by non-adherent PEC. These results revealed two aspects of the effects of E2 on Mphi. Even though E2 was found to enhance Mphi phagocytosis, the anti-bacterial function was suppressed. This suppression may be mediated by the inhibition of both IL-12 and TNF-alpha which play important roles in the protective response against intracellular bacteria.

The Specificity of a Weak γδ TCR Interaction Can Be Modulated by the Glycosylation of the Ligand

The γδ T cell clone LBK5 recognizes the MHC molecule IEk. Here, we demonstrate that the affinity of this interaction is weaker than those typically reported for αβ TCRs that recognize peptide/MHC complexes. Consistent with our previous finding that peptide bound to the IE molecule does not confer specificity, we show that the entire epitope for LBK5 is contained within the polypeptide chains of the molecule, centered around the polymorphic residues 67 and 70 of the IE β-chain. However, LBK5 recognition is profoundly influenced by the N-linked glycosylation at residue 82 of the IE α-chain. Since infected, stressed, or transformed cells often change the posttranslational modifications of their surface glycoproteins, this finding suggests a new way in which γδ T cell Ag recognition can be regulated.

Restricted diversification of T-cells in chronic active Epstein-Barr virus infection: potential inclination to T-lymphoproliferative disease

To assess the abnormal T-cell expansion in chronic active Epstein-Barr virus infection (CAEBV), T-cell antigen receptor (TCR) repertoire was analyzed in four patients with the disease. All fulfilled the diagnostic criteria of CAEBV, presenting with fever, hepatosplenomegaly, cytopenia, abnormal high titers of anti EBV-antibodies, and positive EBV genome of unknown cause. Southern blotting probed with EBV-terminal repeats and TCR Cbeta gene indicated clonal expansion of the infected cells in 3 and 2 patients, respectively. The number of CD4+ HLA-DR+ cells appreciably increased in patients 1 (59%) and 2 (24%), who had a coronary aneurysm and central nervous system involvement, respectively. TCR gene expression examined by the inverse polymerase chain reaction methods revealed that Vbeta gene usages were preferential in all patients (Vbeta7 and Vbeta12: patient 1, Vbeta4: patient 2, Vbeta13: patients 3 and 4), compared with those in healthy controls. Valpha18 gene expression was remarkably high in patients 1 and 2. Moreover, Jbeta gene expression was skewing in the reigning Vbeta clones in all patients. Vbeta4-Jbeta1.5 and Vbeta13-Jbeta1.5 genes were clonally expressed in patients 2 and 4, respectively. These results suggest that CAEBV is associated with the restricted diversity of T-cells, which may stem from the sustained expansion of oligoclonal T-cells possibly driven by conventional viral antigens, but not, superantigens. Although the study is limited by the small number of patients, the unbalanced T-cell repertoire might contribute to the evolution of T-lymphoproliferative disease, otherwise, imply the innate defective immunity to EBV in CAEBV patients.

Interleukin-15 production at the early stage after oral infection with Listeria monocytogenes in mice

We previously reported that exogenous interleukin-15 (IL-15) induces proliferation and activation of intestinal intraepithelial lymphocytes (i-IEL) in naive mice. To investigate the ability of endogenous IL-15 to stimulate i-IEL in vivo, we monitored i-IEL and intestinal epithelial cells (i-EC) in mice after an oral infection with Listeria monocytogenes. Although the populations of alphabeta and gammadelta i-IEL were not significantly changed after the oral infection, the expression level of interferon-gamma (IFN-gamma) was increased both at transcriptional and protein levels, and a conversely marked decrease in interleukin-4 (IL-4) was detected in the i-IEL on day 1 after infection as compared with before infection. The T helper 1 (Th1)-biased response of i-IEL coincided with a peak response of IL-15 production in the i-EC after oral infection. These results suggested that IL-15 produced from i-EC may be at least partly involved in the stimulation of i-IEL to produce IFN-gamma after oral infection with L. monocytogenes.

Antigen-driven clonal accumulation of peritoneal gammadelta T cells in vivo

How the clonality of gammadelta T cells changes in response to exogenous antigens is uncertain. Here we analyzed kinetics of Vgamma1.1 and Vgamma2 T cell clonality after intraperitoneal injection of purified protein derivatives (PPD) by the heterogeneity of the third complementarity determining region (CDR3) length in Vgamma1.1-Jgamma4-Cgamma4 and Vgamma2-Jgamma1-Cgamma1 junctions. The V-J junctions were analyzed in intrahepatic lymphocytes (IHL), spleen cells, and peritoneal exudate cells (PEC) by polyacrylamide gel electrophoresis. Gammadelta T cells expressing Vgamma1.1 and Vgamma2 genes were heterogeneous in normal mice. Accumulation of specific Vgamma1.1 T cell clones was transiently detected 7 days after the injection in PEC, but no accumulation was observed in IHL and spleen cells. The accumulated clones disappeared by 4 weeks. Transient accumulation of Vgamma2 T cell clones was also observed in PEC at the early phase after the injection. These results suggest that gammadelta T cells with specific TCR respond to PPD and temporary accumulate in the peritoneal cavity, but not in liver and spleen.

MHC Class II-Dependent NK1.1+ γδ T Cells Are Induced in Mice by Salmonella Infection

We observed the emergence of a novel population of γδ T cells expressing NK1.1 Ag in the peritoneal cavity of mice infected with Salmonella choleraesuis. The NK1.1+γδ T cells accounted for approximately 20% of all γδ T cells emerging in the peritoneal cavity of C57BL/6 mice and expressed preferentially rearranged Vγ4-Jγ1 and Vδ6.3-Dδ1-Dδ2-Jδ1 genes with N diversity. The γδ T cells proliferated vigorously in response to PHA-treated spleen cells and produced IFN-γ in the culture supernatant. However, spleen cells from Aβb-deficient mice were unable to stimulate the γδ T cells. Furthermore, the NK1.1+γδ T cells were stimulated not only by Chinese hamster ovary (CHO) cells expressing wild-type IAb but also by those expressing IAb/Eα52-68 or IAb/pigeon cytochrome c-derived analogue peptide complex. These proliferation activities were inhibited by mAb specific for IAb chain. Consistent with these findings, the emergence of NK1.1+γδ T cells was reduced in the peritoneal cavity of Aβb-deficient mice after Salmonella infection, whereas NK1.1+γδ T cells were rather abundant in the peritoneal cavity of Salmonella-infected β2m-deficient mice. Moreover, the NK1.1+γδ T cells were easily identified in the thymus of β2m-deficient but not Aβb-deficient mice. Our results indicated that MHC class II expression is essential for development and activation of NK1.1+γδ T cells in the thymus and the periphery.

Development of an Animal Model for Neurocysticercosis: Immune Response in the Central Nervous System Is Characterized by a Predominance of γδ T Cells

Neurocysticercosis is the most common parasitic disease of the central nervous system worldwide. It is caused by the metacestode form of the helminth Taenia solium. Study of the immune response in the human brain has been limited by the chronic progression of the disease, the influence of corticosteroid treatment, and the scarcity of patients who undergo surgical intervention. To better understand the immune response and associated pathology in neurocysticercosis, a mouse model was developed by intracranial infection of BALB/c mice with Mesocestoides corti, a cestode organism related to T. solium. The immune response reveals the presence of abundant inflammatory infiltrates appearing as early as 2 days postinfection in extraparenchymal regions. In contrast, infiltration of immune cells into parenchymal tissue is significantly delayed. There is a natural progression of innate (neutrophils and macrophages), early induced (NK cells and γδ T cells), and adaptive immune responses (αβ T cells and B cells) in infected mice. γδ T cells are the predominant T cell population. A cell-mediated Th1 pathway of cytokine expression is evident in contrast to the previously described Th2 phenotype induced in the periphery.

Regulation by cytokines (IL-12, IL-15, IL-4 and IL-10) of the Vgamma9Vdelta2 T cell response to mycobacterial phosphoantigens in responder and anergic HIV-infected persons

Human Vgamma9Vdelta2 T cells contribute to immunity against intracellular pathogens and recognize nonpeptidic antigens, such as the mycobacterial phosphoantigen TUBAg. HIV infection is associated with a polyclonal decrease of peripheral Vgamma9Vdelta2 T cells and we previously reported that the remaining cells show a proliferative anergy to stimulation with Mycobacterium tuberculosis in 60% of patients. Because of alterations in the Th1/Th2 cytokine balance reported in HIV infection, we analyzed, at the single-cell level, the influence of exogenous IL-4, IL-10, IL-12 and IL-15 on the response to mycobacterial phosphoantigens of gammadelta T cells from HIV-infected patients and healthy donors. We report that the strong gammadelta T cell response to TUBAg is characterized by the rapid and selective production of the Th1/proinflammatory cytokines IFN-gamma and TNF-alpha in responder HIV-infected donors. In addition, a positive regulation by IL-12 and IL-15 of the production of these cytokines by Vgamma9Vdelta2 T cells in response to nonpeptidic ligands was observed, whereas IL-4 and IL-10 had no effect. In contrast, Vgamma9Vdelta2 T cells from the anergic HIV-infected donors had lost the ability to produce Th1 cytokines and were not shifted towards a Th2 profile. Furthermore, neither IL-12 nor IL-15 could reverse this functional anergy. The consequences of these observations are discussed in the context of HIV pathogenesis.

The protective role of T-cell receptor Vgamma1+ T cells in primary infection with Listeria monocytogenes

We have previously reported that the T-cell receptor (TCR) gamma delta+ T cells increase in mice infected with an intracellular bacteria Listeria monocytogenes, and the cells predominantly express Vdelta6 and Vgamma1 genes. In this study, we used a monoclonal antibody (mAb) specific to TCR Vgamma1 to estimate the frequency of Vgamma1+ T cells and we discuss their significance in protection against L. monocytogenes. The spleen, liver and peritoneal exudate cells from mice intraperitoneally infected with L. monocytogenes were analysed by flow cytometry. In all the organs investigated, Vgamma1+ cells increased predominantly among TCR gamma delta+ T cells at an early phase (day 5-7) of the infection. To elucidate the significance of the Vgamma1+ T cells in the protection against L. monocytogenes, mice were depleted of TCR Vgamma1+ gamma delta T cells or all TCR gamma delta+ T cells by intraperitoneal inoculation of anti-Vgamma1 mAb or anti-pan TCR gamma delta mAb, respectively, before infection with L. monocytogenes. The bacterial growth in the spleen and the liver examined on day 5 after the infection increased significantly by the depletion of TCR Vgamma1+ T cells. The numbers of L. monocytogenes in TCR Vgamma1+ T-cell-depleted mice were nearly the same as in mice depleted of all TCR gamma delta+ T cells. These results demonstrated that Vgamma1+ T cells are the predominant population of gamma delta T cells in protection against L. monocytogenes at the early phase of the primary infection.

Restraint stress-induced immunosuppression by inhibiting leukocyte migration and Th1 cytokine expression during the intraperitoneal infection of Listeria monocytogenes

In this study, a murine model of Listeria monocytogenes infection was used to investigate effects of restraint stress (RST) on host defense. We observed that the L. monocytogenes infection as well as RST induced an elevation of endogenous corticosterone (CORT) levels and RST synergistically enhanced endogenous CORT levels during the listerial infection. RST suppressed the migration of leukocytes including macrophages, neutrophils, NK cells and lymphocytes into the peritoneal cavities after the intraperitoneal inoculation of L. monocytogenes. RST also suppressed the increase of the surface MHC class II antigen expression in both peritoneal macrophages and B cells during the listerial infection. Interestingly, gene expression of iNOS, MCP-1 (JE) and Th1-type cytokines including IFN-gamma and IL-12 was down-regulated but Th2-type cytokine (IL-4 and IL-6) gene expression in the PEC was rather up-regulated on day 7 after infection, indicating that Th2-type immune response is more resistant to the elevated endogenous CORT levels than Th1-type response. Treatment of mice with RU486, a glucocorticoid receptor antagonist, restored the immune responses suppressed by RST to their normal levels in the infected mice, suggesting that the RST-induced elevation of endogenous corticosterone levels is mainly responsible for the induction of the immunosuppressive events during L. monocytogenes infection.

The role of gammadelta T cells in induction of bacterial antigen-specific protective CD8+ cytotoxic T cells in immune response against the intracellular bacteria Listeria monocytogenes

The role of T-cell receptor (TCR) gammadelta T cells in the induction of protective TCR alphabeta T cells against infection by the intracellular bacteria Listeria monocytogenes was analysed. We found that depletion of gammadelta T cells by anti-TCR delta monoclonal antibody treatment before intravenous immunization of mice with a sublethal dose of viable L. monocytogenes resulted in reduction of protection against secondary challenge infection in the immunized mice. The gammadelta T-cell depletion also reduced induction of protective alphabeta T cells capable of transferring the protection against challenge infection of L. monocytogenes into naive mice. Furthermore, the protective T cells that were affected by the gammadelta T-cell depletion were suggested to be CD8+ cytotoxic T cells rather than CD4+ T cells by the following observations. First, induction of cytotoxic T lymphocytes specific to a L. monocytogenes-derived H-2Kd-restricted peptide (listeriolysin O 91-99) was significantly suppressed by gammadelta T-cell depletion before immunization. Second, gammadelta T-cell depletion did not affect cytokine production and proliferation of T cells from immunized mice in response to in vitro stimulation with heat-killed Listeria which preferentially stimulates CD4+ T cells. Third, CD8+ alphabeta T cells from control immunized mice transferred protection against infection of L. monocytogenes into naive mice but only a limited degree of protection was transferred by CD8+ T cells from the gammadelta T-cell-depleted immunized mice; and fourth, CD4+ alphabeta T cells from the gammadelta T-cell-depleted mice transferred a similar level of protection as those from the control immunized mice. All these results suggest that gammadelta T cells participate in establishment of protective immunity against intracellular bacteria by supporting priming of bacterial antigen-specific CD8+ cytotoxic T cells.

Regulation and function of T-cell-mediated immunity during Toxoplasma gondii infection

The intracellular protozoan Toxoplasma gondii is a widespread opportunistic parasite of humans and animals. Normally, T. gondii establishes itself within brain and skeletal muscle tissues, persisting for the life of the host. Initiating and sustaining strong T-cell-mediated immunity is crucial in preventing the emergence of T. gondii as a serious pathogen. The parasite induces high levels of gamma interferon (IFN-gamma) during initial infection as a result of early T-cell as well as natural killer (NK) cell activation. Induction of interleukin-12 by macrophages is a major mechanism driving early IFN-gamma synthesis. The latter cytokine, in addition to promoting the differentiation of Th1 effectors, is important in macrophage activation and acquisition of microbicidal functions, such as nitric oxide release. During chronic infection, parasite-specific T lymphocytes release high levels of IFN-gamma, which is required to prevent cyst reactivation. T-cell-mediated cytolytic activity against infected cells, while easily demonstrable, plays a secondary role to inflammatory cytokine production. While part of the clinical manifestations of toxoplasmosis results from direct tissue destruction by the parasite, inflammatory cytokine-mediated immunopathologic changes may also contribute to disease progression.

Prostaglandin E2 Protects Against Liver Injury After Escherichia coli Infection but Hampers the Resolution of the Infection in Mice

cAMP-increasing agents such as prostaglandin E2 (PGE2) are known to protect against LPS-induced liver injury by down-regulating the production of inflammatory cytokines such as TNF-α. However, the effects of such reagents on host defense against bacterial infection remain unknown. We show here that in vivo administration of PGE2 significantly protected mice against liver injury after Escherichia coli infection but hampered the resolution of the infection. PGE2 significantly suppressed circulating TNF-α and IL-12 levels but increased the IL-10 production after E. coli challenge. PGE2 inhibited the emergence of γδ T cells in the peritoneal cavity, which are important for host defense against E. coli, and deteriorated bacterial exclusion in the peritoneal cavity after E. coli challenge. These results suggested that PGE2 affects host defense mechanisms against E. coli infection through modulation of cytokine production and γδ T cell accumulation.

Protective roles of gamma delta T cells and interleukin-15 in Escherichia coli infection in mice

The number of gamma delta T cells in the peritoneal cavity was increased after an intraperitoneal (i.p.) infection with Escherichia coli in lipopolysaccharide (LPS)-responsive C3H/HeN mice but not in LPS-hyporesponsive C3H/HeJ mice. The gamma delta T cells preferentially expressed invariant Vgamma6 and Vdelta1 chains and proliferated to produce a large amount of gamma interferon in the presence of LPS. Mice depleted of gamma delta T cells by T-cell receptor delta gene mutation showed impaired resistance against E. coli as assessed by bacterial growth. Macrophages from C3H/HeN mice infected with E. coli expressed higher levels of interleukin-15 (IL-15) mRNA than those from the infected C3H/HeJ mice. Administration of anti-IL-15 monoclonal antibody inhibited, albeit partially, the appearance of gamma delta T cells in C3H/HeN mice after E. coli infection and diminished the host defense against the infection. These results suggest that LPS-stimulated gamma delta T cells play an important role in the host defense against E. coli infection and that IL-15 may be partly involved in the protection via an increase in the gamma delta T cells.

Early Preferential Stimulation of γδ T Cells by TNF-α

Although recent findings indicate that γδ T cells influence both early innate and Ag-specific adaptive host responses, it has remained unclear what triggers γδ T cell reactivity. Investigating very early T cell activation in mouse and human models of bacterial infection, we measured CD69 expression as an indicator of early cellular activation. Both murine αβ and γδ T cells responded polyclonally to systemic bacterial infections, and to LPS. However, γδ T cells responded more strongly to the bacteria and to LPS. In vitro LPS-stimulated human T cells showed a similar differential response pattern. We identified TNF-α as mediator of the early differential T cell activation, and of differential proliferative responses. The stronger response of γδ T cells to TNF-α was correlated with higher inducible expression levels of TNF-Rp75. Among unstimulated splenocytes, more γδ T cells than αβ T cells expressed CD44 at high levels. The data suggest that TNF-Rp75 determines the differential T cell reactivity, and that most γδ T cells in the normal spleen are present in a presensitized state. As TNF-α stimulates activated T cells, it may early preferentially connect γδ T cell functions with those of cells that produce this cytokine, including activated innate effector cells and Ag-stimulated T lymphocytes.

IL-15 Enhances the Response of Human γδ T Cells to Nonpetide Microbial Antigens

Human γδ T cells have the ability to rapidly expand and produce IFN-γ in response to nonpeptide Ags of microbial pathogens, in particular a class of compounds known as the prenyl phosphates. We investigated the ability of IL-15, a T cell growth factor, to modulate prenyl phosphate-induced γδ T cell proliferation and cytokine production. IL-15 significantly enhanced the expansion of γδ T cells in the peripheral blood after stimulation in vitro with isopentenyl pyrophosphate. Moreover, using γδ T cell clones, we determined that IL-15-induced T cell proliferation was dependent on the IL-2Rβ chain but not the IL-2Rα chain. We therefore studied the IL-15Rα chain expression in human γδ T cells in the presence or absence of nonpeptide Ags. We found IL-15Rα mRNA expression in IL-15-stimulated and Ag-stimulated human γδ T cells but not in resting γδ T cells. Although IL-15 itself had little effect on the production of IFN-γ, IL-15 plus IL-12 acted synergistically to augment IFN-γ production by γδ T cells. Moreover, we showed that this increase in IFN-γ could be explained by the dual activation of STAT1 and STAT4 by IL-15 and IL-12, respectively. Taken together, these results suggest that IL-15 may contribute to activation of human γδ T cells in the immune response to microbial pathogens.

Gammadelta+ and CD4+ alphabeta+ human T cell subset responses upon stimulation with various Mycobacterium tuberculosis soluble extracts

By using a flow cytometric technique which allows direct identification of proliferating cells within mixed cell populations, we have previously described that soluble extracts obtained from Mycobacterium tuberculosis or M. avium represent strong stimuli for human gammadelta+ T cells. In the present study, we demonstrate that the protocol used for the preparation of M. tuberculosis soluble extracts may have an impact on their gammadelta+ T cell stimulatory capacity. In agreement with our previous data, soluble extracts prepared from bacteria killed at 85 degrees C and directly disrupted by prolonged sonication (TBe), elicited a strong proliferation of gammadelta+ T cells after 6-7 days of stimulation. In contrast, when soluble extracts were obtained from bacteria autoclaved (121 degrees C, 25 min) and then washed by centrifugation, a predominant proportion of CD4+ alphabeta+ T cells was achieved in the responding population. The stimulatory activity for gammadelta+ T cells was recovered in the supernatant of the autoclaved bacteria, indicating that autoclaving of M. tuberculosis bacilli releases an antigen(s) into the supernatant which stimulates human gammadelta+ T cells. While protease digestion of TBe only partially reduced its stimulatory capacity on gammadelta+ T cells, the stimulatory component(s) released into the supernatant after autoclavation of bacilli was found to be sensitive to protease digestion. Interestingly, in contrast to the preponderant proportion of gammadelta+ T cells induced in the responding population by unfractionated TBe, when the extract was fractionated by fast performance liquid chromatography (FPLC), most of the fractions exhibited a strong stimulatory capacity on CD4+ alphabeta+ T cells only. The gammadelta+ T cell stimulatory activity was confined to the low molecular weight range FPLC fractions. Such results may suggest a possible regulatory role of gammadelta+ T cells on CD4+ alphabeta+ T cells.

The T cell receptor subsets of lymphocytes in bronchoalveolar lavage in patients with active pulmonary tuberculosis

STUDY OBJECTIVE

To determine whether or not the levels of gamma/delta lymphocytes increase in bronchoalveolar lavage (BAL) fluid from patients with pulmonary tuberculosis.

DESIGN

Prospective data collection relating to cells in BAL fluid and peripheral blood mononuclear cells (PBMC) from patients with pulmonary tuberculosis and control subjects.

SETTING

A university hospital, from March 1990 to December 1993.

PATIENTS

Thirteen patients with pulmonary tuberculosis who were diagnosed by culture of Mycobacterium tuberculosis from their sputum of BAL fluid and/or clinical response were enrolled in the study. Fifteen healthy volunteers participated as control subjects.

MEASUREMENTS AND RESULTS

The differential cell counts in BAL fluid were made by Diff-Quik stain. The percentages of T-cell receptor (TCR) (gamma/delta and alpha/beta)-positive lymphocytes and interleukin 2 (IL-2) receptor-positive CD3 lymphocytes in BAL fluid and peripheral blood were measured by dual scan with flow-cytometry. The percentage and absolute number of lymphocytes and the percentages of CD3+, IL2R+ lymphocytes in BAL fluid significantly increased in patients with tuberculosis when compared with those of control subjects. The percentages and numbers of gamma/delta and alpha/beta TCR-positive lymphocytes in BAL fluid and PBMC from patients with tuberculosis and indistinguishable from those of control subjects.

CONCLUSIONS

gamma/delta Lymphocytes do not appear to have as much meaning in patients as they do in animal studies.

Lifespan of gamma/delta T cells

Information on the turnover and lifespan of murine gamma/delta cells was obtained by administering the DNA precursor, bromodeoxyuridine (BrdU), in the drinking water and staining lymphoid cells for BrdU incorporation. For TCR-gamma/delta (Vgamma2) transgenic mice, nearly all gamma/delta thymocytes became BrdU+ within 2 d and were released rapidly into the peripheral lymphoid tissues. These recent thymic emigrants (RTEs) underwent phenotypic maturation in the periphery for several days, but most of these cells died within 4 wk. In adult thymectomized (ATx) transgenic mice, only a small proportion of gamma/delta cells survived as long-lived cells; most of these cells had a slow turnover and retained a naive phenotype. As in transgenic mice, the majority of RTEs generated in normal mice (C57BL/6) appeared to have a restricted lifespan as naive cells. However, in marked contrast to TCR transgenic mice, most of the gamma/delta cells surviving in ATx normal mice had a rapid turnover and displayed an activated/memory phenotype, implying a chronic response to environmental antigens. Hence, in normal mice many gamma/delta RTEs did not die but switched to memory cells.

The surface epithelium of recurrent infected palatine tonsils is rich in gammadelta T cells

Using a large panel of MoAbs in quantitative morphometric analysis of immunohistochemically stained tissue sections, we compared the frequency and distribution of immune cells in palatine tonsils from patients with recurrent tonsillitis (RT) and patients with idiopathic tonsillar hypertrophy (ITH). We found that differences between the two patient groups in leucocyte populations were limited to the surface epithelium, whereas the cellular composition of interfollicular and follicular areas was similar. Most intraepithelial lymphocytes were CD8+ T cells in both groups. However, the number of intraepithelial T cells was significantly higher in RT compared with ITH. This was due to a selective increase in the number of intraepithelial CD8+ gammadelta T cells utilizing Vdelta1 and Vgamma9. In both patient groups the majority of the intraepithelial gammadelta T cells expressed Vdelta1 and Vgamma9. Subepithelially, gammadelta T cells utilizing Vgamma9 dominated over cells utilizing Vgamma8, while equal proportions expressed Vdelta1 and Vdelta2. These results suggest that cells utilizing the otherwise rare combination Vdelta1/Vgamma9 in their T cell receptors (TCR) may constitute a major gammadelta T cell population in palatine tonsils and are probably reactive to antigens specific to the tonsillar milieu. Furthermore, they indicate that preferentially this gammadelta T cell subpopulation is involved in immune reactions within the surface epithelium in RT. We speculate that gammadelta T cells are involved in clearing infectious bacteria at the tonsillar surface and in limiting inflammatory responses in the tonsils. Both local expansion and infiltration of blood cells probably contribute to the high numbers of gammadelta T cells in RT patients.