The role of gamma delta T cells in priming macrophages to produce tumor necrosis factor-alpha

Tyrosine Kinase Inhibition Activates Intratumoral γδ T Cells in Gastrointestinal Stromal Tumor

γδ T cells are a rare but potent subset of T cells with pleiotropic functions. They commonly reside within tumors but the response of γδ T cells to tyrosine kinase inhibition is unknown. To address this, we studied a genetically engineered mouse model of gastrointestinal stromal tumor (GIST) driven by oncogenic Kit signaling that responds to the Kit inhibitor imatinib. At baseline, γδ T cells were antitumoral, as blockade of either γδ T-cell receptor or IL17A increased tumor weight and decreased antitumor immunity. However, imatinib therapy further stimulated intratumoral γδ T cells, as determined by flow cytometry and single-cell RNA sequencing (scRNA-seq). Imatinib expanded a highly activated γδ T-cell subset with increased IL17A production and higher expression of immune checkpoints and cytolytic effector molecules. Consistent with the mouse model, γδ T cells produced IL17A in fresh human GIST specimens, and imatinib treatment increased γδ T-cell gene signatures, as measured by bulk tumor RNA-seq. Furthermore, tumor γδ T cells correlated with survival in patients with GIST. Our findings highlight the interplay between tumor cell oncogene signaling and antitumor immune responses and identify γδ T cells as targets for immunotherapy in GIST.

Dermal γδ T-Cells Can Be Activated by Mitochondrial Damage-Associated Molecular Patterns

Background

Gamma delta T-cells have been shown to be important to the early immunoinflammatory response to injury, independent of infection. This unique T-cell population acts to regulate cell trafficking and the release of cytokines and growth factors. We propose this sterile inflammatory response is in part associated with damage associated molecular patterns (DAMPs) generated by major injury, such as burn, and mediated via toll-like receptors (TLRs). It is unknown whether DAMPs can activate resident γδ T-cells that reside in skin.

Methods

Gamma delta T-cells were isolated from the skin of male C57BL/6 mice by enzymatic digestion. Mitochondrial DAMPs (MTDs) were generated from mitochondria isolated from mouse livers by sonication and centrifugation. Dermal γδ T-cells were incubated with MTDs (0–500 μg/ml) for 24 hr and cells and supernatants were collected for analysis.

Results

MTDs activated dermal γδ T-cells, as evidenced by increased TLR2 and TLR4 expression following in vitro exposure. MTDs also induced the production of inflammatory cytokines (IL-1β, IL-6), and growth factors (PDGF and VEGF) by γδ T-cells.

Conclusions

These findings herein support the concept that MTDs released after tissue/cellular injury are capable of activating dermal γδ T-cells. We propose that the activation of this unique T-cell population is central in the initiation of sterile inflammation and also contributes to the subsequent healing processes.

Type I NKT-cell-mediated TNF-α is a positive regulator of NLRP3 inflammasome priming

The NLRP3 inflammasome plays a crucial role in the innate immune response to pathogens and exogenous or endogenous danger signals. Its activity must be precisely and tightly regulated to generate tailored immune responses. However, the immune cell subsets and cytokines controlling NLRP3 inflammasome activity are still poorly understood. Here, we have shown a link between NKT-cell-mediated TNF-α and NLRP3 inflammasome activity. The NLRP3 inflammasome in APCs was critical to potentiate NKT-cell-mediated immune responses, since C57BL/6 NLRP3 inflammasome-deficient mice exhibited reduced responsiveness to α-galactosylceramide. Importantly, NKT cells were found to act as regulators of NLRP3 inflammasome signaling, as NKT-cell-derived TNF-α was required for optimal IL-1β and IL-18 production by myeloid cells in response to α-galactosylceramide, by acting on the NLRP3 inflammasome priming step. Thus, NKT cells play a role in the positive regulation of NLRP3 inflammasome priming by mediating the production of TNF-α, thus demonstrating another means by which NKT cells control early inflammation.

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.

Mitochondrial damage-associated molecular patterns activate γδ T-cells

Gamma delta T-cells have been shown to be important in the early immunoinflammatory response to injury, which can be independent of infection. This sterile inflammatory response is believed to be, in part, associated with danger-associated molecular patterns (DAMPs). Mitochondrial DAMPs (MTDs) have been shown to be important in trauma-induced neutrophil activation, but it is unknown whether MTDs activate other innate immune cells, such as γδ T-cells. To study this, splenic CD3(+) γδ T-cells were isolated from αβ T-cell-deficient C57BL/6 mice and mitochondria isolated from wild type mouse livers. MTDs were isolated from mitochondria by sonication and centrifugation. Gamma delta T-cells were incubated with various concentrations of MTDs (0-500 µg/ml) for 24 h. T-cells were phenotyped for TLR expression by flow cytometry and the supernatants assayed for cytokine and growth factor content. MTDs caused a dose-dependent increase in TLR2 and TLR4 expression by γδ T-cells. Both the percentage of cells positive for TLRs and the degree of expression increased. MTDs also induced the production of IL-1β, IL-6, IL-10, RANTES, fibroblast growth factor-basic and vascular endothelial growth factor by γδ T-cells. These findings support the concept that the MTDs released after tissue/cellular injury are capable of activating γδ T-cells, thus initiating sterile inflammation, as well as subsequent healing processes.

Psoriasis, hepatitis B, and the tumor necrosis factor-alpha inhibitory agents: a review and recommendations for management

BACKGROUND

Tumor necrosis factor inhibitory agents are currently considered to be contraindicated in psoriatic patients with hepatitis B.

OBJECTIVE

We aim to provide guidance to dermatologists on the use of tumor necrosis factor inhibitor therapy in these patients.

METHODS

The current literature was reviewed regarding the use of tumor necrosis factor-alpha inhibitory agents (etanercept, adalimumab, and infliximab) in psoriatic patients with particular reference to hepatitis B infection.

RESULTS

Tumor necrosis factor-alpha inhibitor therapy may result in reactivated hepatitis B in hepatitis B surface antigen-positive patients with psoriasis. This also occurs, although less frequently in patients with an isolated positive hepatitis B core antibody. Thus, all psoriasis patients should be screened for hepatitis B surface antigen plus hepatitis B core antibody prior to the initiation of tumor necrosis factor-alpha inhibitor therapy. Infliximab has been associated with more reactivation cases than the other 2 agents and fatalities have been reported with this agent. Evidence is presented that the risk of reactivation can be greatly minimized or eliminated by early or pre-emptive antiviral therapy.

LIMITATIONS

The data is largely based on small case series that are retrospective in nature.

CONCLUSIONS

Hepatitis B screening is essential prior to the initiation of tumor necrosis factor-alpha inhibitor therapy. Psoriatic patients found to be hepatitis B surface antigen or hepatitis B core antibody-positive should be referred to an appropriate specialist for evaluation and therapy. This would allow for the safe use of tumor necrosis factor-alpha inhibitors in psoriatic patients despite recently published guidelines to the contrary.

Granulocyte colony-stimulating factor affects the distribution and clonality of TRGV and TRDV repertoire of T cells and graft-versus-host disease

Background

The immune modulatory effect of granulocyte colony-stimulating factor (G-CSF) on T cells resulted in an unexpected low incidence of graft-versus-host disease (GVHD) in allogeneic peripheral blood stem cell transplantation (allo-PBSCT). Recent data indicated that gamma delta⁺ T cells might participate in mediating graft-versus-host disease (GVHD) and graft-versus-leukemia (GVL) effect after allogeneic hematopoietic stem cell transplantation. However, whether G-CSF could influence the T cell receptors (TCR) of gamma delta⁺ T cells (TRGV and TRDV repertoire) remains unclear. To further characterize this feature, we compared the distribution and clonality of TRGV and TRDV repertoire of T cells before and after G-CSF mobilization and investigated the association between the changes of TCR repertoire and GVHD in patients undergoing G-CSF mobilized allo-PBSCT.

Methods

The complementarity-determining region 3 (CDR3) sizes of three TRGV and eight TRDV subfamily genes were analyzed in peripheral blood mononuclear cells (PBMCs) from 20 donors before and after G-CSF mobilization, using RT-PCR and genescan technique. To determine the expression levels of TRGV subfamily genes, we performed quantitative analysis of TRGVI~III subfamilies by real-time PCR.

Results

The expression levels of three TRGV subfamilies were significantly decreased after G-CSF mobilization (P = 0.015, 0.009 and 0.006, respectively). The pattern of TRGV subfamily expression levels was TRGVII >TRGV I >TRGV III before mobilization, and changed to TRGV I >TRGV II >TRGV III after G-CSF mobilization. The expression frequencies of TRGV and TRDV subfamilies changed at different levels after G-CSF mobilization. Most TRGV and TRDV subfamilies revealed polyclonality from pre-G-CSF-mobilized and G-CSF-mobilized samples. Oligoclonality was detected in TRGV and TRDV subfamilies in 3 donors before mobilization and in another 4 donors after G-CSF mobilization, distributed in TRGVII, TRDV1, TRDV3 and TRDV6, respectively. Significant positive association was observed between the invariable clonality of TRDV1 gene repertoire after G-CSF mobilization and low incidence of GVHD in recipients (P = 0.015, OR = 0.047).

Conclusions

G-CSF mobilization not only influences the distribution and expression levels of TRGV and TRDV repertoire, but also changes the clonality of gamma delta⁺ T cells. This alteration of TRGV and TRDV repertoire might play a role in mediating GVHD in G-CSF mobilized allo-PBSCT.

Murine and bovine γδ T cells enhance innate immunity against Brucella abortus infections

γδ T cells have been postulated to act as a first line of defense against infectious agents, particularly intracellular pathogens, representing an important link between the innate and adaptive immune responses. Human γδ T cells expand in the blood of brucellosis patients and are active against Brucella in vitro. However, the role of γδ T cells in vivo during experimental brucellosis has not been studied. Here we report TCRδ^−/− mice are more susceptible to B. abortus infection than C57BL/6 mice at one week post-infection as measured by splenic colonization and splenomegaly. An increase in TCRγδ cells was observed in the spleens of B. abortus-infected C57BL/6 mice, which peaked at two weeks post-infection and occurred concomitantly with diminished brucellae. γδ T cells were the major source of IL-17 following infection and also produced IFN-γ. Depletion of γδ T cells from C57BL/6, IL-17Rα^−/−, and GMCSF^−/− mice enhanced susceptibility to B. abortus infection although this susceptibility was unaltered in the mutant mice; however, when γδ T cells were depleted from IFN-γ^−/− mice, enhanced susceptibility was observed. Neutralization of γδ T cells in the absence of TNF-α did not further impair immunity. In the absence of TNF-α or γδ T cells, B. abortus-infected mice showed enhanced IFN-γ, suggesting that they augmented production to compensate for the loss of γδ T cells and/or TNF-α. While the protective role of γδ T cells was TNF-α-dependent, γδ T cells were not the major source of TNF-α and activation of γδ T cells following B. abortus infection was TNF-α-independent. Additionally, bovine TCRγδ cells were found to respond rapidly to B. abortus infection upon co-culture with autologous macrophages and could impair the intramacrophage replication of B. abortus via IFN-γ. Collectively, these results demonstrate γδ T cells are important for early protection to B. abortus infections.

Up-regulation of cell surface Toll-like receptors on circulating gammadelta T-cells following burn injury

Burn injury is associated with profound inflammation and activation of the innate immune system involving gammadelta T-cells. Similarly, Toll-like receptors (TLR) are associated with activation of the innate immune response; however, it is unclear whether TLR expression is altered in gammadelta T-cells after major burn injury. To study this, male C57BL/6 mice were subjected to burn injury (25% TBSA) and 1 or 7 days thereafter, blood and spleen cells were isolated and subjected to FACs analysis for TLRs and other phenotypic markers (gammadelta TCR, alphabeta TCR, CD69, CD120b). A marked increase in the number of circulating gammadelta T-cells was observed at 24h post-burn (14% vs. 4%) and a higher percentage of these cells expressed TLR-2. TLR-4 expression was also increased post-burn, but to a lesser degree. These changes in TLR expression were not associated with altered CD69 or CD120b expression in gammadelta T-cells. The mobilization of, and increased TLR expression in, gammadelta T-cells was transient, as phenotypic changes were not evident at 7 days post-burn or in gammadelta T-cells from the circulation or spleen. The increases in TLR expression were not observed in alphabeta T-cells after burn injury. In conclusion, 24h after burn injury mobilization of gammadelta T-cells with increased TLR expression was observed. This finding suggests that this unique T-cell population is critical in the innate immune response to injury, possibly through the recognition of danger signals by TLRs.

Gammadelta T-cells: potential regulators of the post-burn inflammatory response

Severe burn induces an immunopathological response that contributes to the development of a systemic inflammatory response (SIRS) and subsequent multiple organ failure. While, multiple immune cells type (T-cells, macrophages, neutrophils) are involved in this response, recent evidence suggests that a unique T-cell subset, gammadelta T-cells are central in the response to injury. While gammadelta T-cells represent only a small percentage of the total T-cell population, they display specific functional characteristics that uniquely position them in the immune/inflammatory axis to influence a number of important aspects of the body's response to burn. This review will focus on the potential regulator role of gammadelta T-cells in immunopathological response following burn and thereby their potential as therapeutic targets for affecting inflammation and healing.

Immune evasion by pathogens of bovine respiratory disease complex

Bovine respiratory tract disease is a multi-factorial disease complex involving several viruses and bacteria. Viruses that play prominent roles in causing the bovine respiratory disease complex include bovine herpesvirus-1, bovine respiratory syncytial virus, bovine viral diarrhea virus and parinfluenza-3 virus. Bacteria that play prominent roles in this disease complex are Mannheimia haemolytica and Mycoplasma bovis. Other bacteria that infect the bovine respiratory tract of cattle are Histophilus (Haemophilus) somni and Pasteurella multocida. Frequently, severe respiratory tract disease in cattle is associated with concurrent infections of these pathogens. Like other pathogens, the viral and bacterial pathogens of this disease complex have co-evolved with their hosts over millions of years. As much as the hosts have diversified and fine-tuned the components of their immune system, the pathogens have also evolved diverse and sophisticated strategies to evade the host immune responses. These pathogens have developed intricate mechanisms to thwart both the innate and adaptive arms of the immune responses of their hosts. This review presents an overview of the strategies by which the pathogens suppress host immune responses, as well as the strategies by which the pathogens modify themselves or their locations in the host to evade host immune responses. These immune evasion strategies likely contribute to the failure of currently-available vaccines to provide complete protection to cattle against these pathogens.

Regulation of the postburn wound inflammatory response by gammadelta T-cells

Healing of the burn injury site is a critical component of the patient's successful recovery from this form of trauma. Previous studies from our laboratory have demonstrated that gammadelta T-cells via the production of growth factors are important in burn wound healing. Nonetheless, the role of these cells in burn wound inflammation remains unknown. To study this, wild-type (WT) and gammadelta T-cell receptor-deficient (delta TCR) C57BL/6 male mice were subjected to burn injury or sham procedure. Wound cells were collected by implantation of polyvinyl alcohol sponges beneath the burn site in injured mice or beneath uninjured skin in sham mice. At 3 days after injury, infiltrating cells, wound fluid, and skin were collected for analysis. Burn injury markedly increased skin tumor necrosis factor-alpha (TNF-alpha) and monocyte chemoattractant protein 1 levels. In WT mice, the numbers of infiltrating cells were similar between nonburn wounds and burn wounds. In contrast, deltaTCRmice displayed a 6-fold reduction in the cellular infiltrate. Burn injury in WT mice caused a marked increase in burn wound TNF-alpha, monocyte chemoattractant protein 1, and interleukin 6 content as compared with nonburn wounds, whereas in delta TCRmice, the burn-induced increase of TNF-alpha and interleukin 6 was not observed. The wound cell infiltrate at 3 days postinjury was devoid of gammadelta T-cells in WT mice. It was predominately of myeloid origin expressing high levels of CD11b and F4/80. In conclusion, these findings suggest that resident gammadelta T-cells are important in the recruitment of inflammatory cells and regulation of the inflammatory response at the wound site after thermal injury.

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.

Failure of antigen-stimulated gammadelta T cells and CD4+ T cells from sensitized cattle to upregulate nitric oxide and mycobactericidal activity of autologous Mycobacterium avium subsp. paratuberculosis-infected macrophages

The function of gammadelta T cells during ruminant paratuberculosis (Johne's disease) is presently unknown. An ex vivo system was used to test the hypothesis that gammadelta T cells are capable of activating Mycobacterium avium subsp. paratuberculosis-(M. paratuberculosis)-infected macrophages. Peripheral blood-derived macrophages were infected in vitro with live M. paratuberculosis, and autologous LN-derived gammadelta T cells or CD4+ T cells were co-cultured with infected macrophages for 48h, at which time bacterial survival as well as production of nitrites and IFN-gamma was evaluated. Incubation of M. paratuberculosis-infected macrophages with autologous gammadelta T cells did not result in reduced intracellular bacterial viability compared to infected macrophage cultures without added T cells. IFN-gamma production by-infected cultures containing added gammadelta T cells was not enhanced compared to that of infected macrophages alone. Although infection of macrophage cultures caused increased production of nitrites at both post-infection day (PID) 0 and PID 60, the addition of gammadelta T cells did not further increase nitrite production. In contrast, addition of PPD-stimulated CD4+ T cells obtained at PID 60 to M. paratuberculosis-infected macrophages resulted in significantly increased IFN-gamma production compared to cultures without added T cells or cultures containing unstimulated CD4+ T cells or unstimulated or antigen-stimulated gammadelta T cells. However, the increased production of IFN-gamma by co-cultures containing PPD-stimulated CD4+ T cells did not result in increased bacterial killing or increased production of nitrites compared to cultures without added T cells. In additional in vitro experiments, M. paratuberculosis-infected macrophages, but not uninfected macrophages, were unable to increase nitrite production when stimulated with recombinant IFN-gamma. Taken together, the data suggest that (1) gammadelta T cells do not produce significant IFN-gamma and do not significantly increase NO production from M. paratuberculosis-infected macrophages in vitro, (2) the production of significant IFN-gamma by antigen-stimulated CD4+ T cells from infected calves is insufficient to enhance mycobacterial killing or nitrite production by infected macrophages, and (3) macrophages may have an impaired NO response following intracellular M. paratuberculosis infection, even in the presence of significant concentrations of IFN-gamma.

T cells of the gammadelta T-cell receptor lineage play an important role in the postburn wound healing process

Although gammadelta T cells have been implicated in various aspects of the dermal wound healing process, their role in postburn wound healing processes has not been investigated. To study this, we subjected mice deficient in gammadelta T cells (ie, T-cell receptor delta gene [delta TCR]) and wild-type (WT; C57BL6J) mice to burn injury (25% TBSA) or sham treatment; skin samples were isolated 3 days later. Marked inflammation of the injury site was observed in WT mice but was markedly reduced in delta TCR mice. Postinjury fibroblast growth factor, platelet-derived growth factor granulocyte-colony stimulating factor levels, and nitrite/nitrate were elevated in skin samples from injured WT mice, whereas skin tissue levels of these growth factors and inflammatory mediators was significantly atteunuated in delta TCRmice. In conclusion, these findings support the concept that gammadelta T cells are important to postburn wound healing via the production of growth factors and, potentially, regulation of inducible nitric oxide synthase activation.

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.

gammadelta T cells regulate the early inflammatory response to bordetella pertussis infection in the murine respiratory tract

The role of gammadelta T cells in the regulation of pulmonary inflammation following Bordetella pertussis infection was investigated. Using a well-characterized murine aerosol challenge model, inflammatory events in mice with targeted disruption of the T-cell receptor delta-chain gene (gammadelta TCR-/- mice) were compared with those in wild-type animals. Early following challenge with B. pertussis, gammadelta TCR-/- mice exhibited greater pulmonary inflammation, as measured by intra-alveolar albumin leakage and lesion histomorphometry, yet had lower contemporaneous bacterial lung loads. The larger numbers of neutrophils and macrophages and the greater concentration of the neutrophil marker myeloperoxidase in bronchoalveolar lavage fluid from gammadelta TCR-/- mice at this time suggested that differences in lung injury were mediated through increased leukocyte trafficking into infected alveoli. Furthermore, flow cytometric analysis found the pattern of recruitment of natural killer (NK) and NK receptor+ T cells into airspaces differed between the two mouse types over the same time period. Taken together, these findings suggest a regulatory influence for gammadelta T cells over the early pulmonary inflammatory response to bacterial infection. The absence of gammadelta T cells also influenced the subsequent adaptive immune response to specific bacterial components, as evidenced by a shift from a Th1 to a Th2 type response against the B. pertussis virulence factor filamentous hemagglutinin in gammadelta TCR-/- mice. The findings are relevant to the study of conditions such as neonatal B. pertussis infection and acute respiratory distress syndrome where gammadelta T cell dysfunction has been implicated in the inflammatory process.

Critical role of host gammadelta T cells in experimental acute graft-versus-host disease

Gammadelta T cells localize to target tissues of graft-versus-host disease (GVHD) and therefore we investigated the role of host gammadelta T cells in the pathogenesis of acute GVHD in several well-characterized allogeneic bone marrow transplantation (BMT) models. Depletion of host gammadelta T cells in wild-type (wt) B6 recipients by administration of anti-T-cell receptor (TCR) gammadelta monoclonal antibody reduced GVHD, and gammadelta T-cell-deficient (gammadelta-/-) BM transplant recipients experienced markedly improved survival compared with normal controls (63% vs 10%, P < .001). gammadelta T cells were responsible for this difference because reconstitution of gammadelta-/- recipients with gammadelta T cells restored GVHD mortality. gammadelta-/- recipients showed decreased serum levels of tumor necrosis factor alpha (TNF-alpha), less GVHD histopathologic damage, and reduced donor T-cell expansion. Mechanistic analysis of this phenomenon demonstrated that dendritic cells (DCs) from gammadelta-/- recipients exhibited less allostimulatory capacity compared to wt DCs after irradiation. Normal DCs derived from BM caused greater allogeneic T-cell proliferation when cocultured with gammadelta T cells than DCs cocultured with medium alone. This enhancement did not depend on interferon gamma (IFN-gamma), TNF-alpha, or CD40 ligand but did depend on cell-to-cell contact. These data demonstrated that the host gammadelta T cells exacerbate GVHD by enhancing the allostimulatory capacity of host antigen-presenting cells.

The role of γδ T cells in the regulation of neutrophil-mediated tissue damage after thermal injury

Thermal injury induces an inflammatory response that contributes to the development of secondary tissue damage. Neutrophil recruitment and activation are in part responsible for this tissue damage. Although gammadelta T cells have been shown to regulate the inflammatory responses in tissues that are prone to neutrophil-mediated injury post-burn, their role in the induction of secondary tissue injury post-burn remains unknown. To study this, gammadelta T cell-deficient (gammadelta TCR-/-) and wild-type (WT) mice were subjected to thermal injury or sham procedure, and tissue samples were isolated 1-24 h thereafter. Burn injury induced neutrophil accumulation in the lung and small intestines of WT mice at 1-3 h post-injury. No such increase in neutrophil tissue content was observed in gammadelta TCR-/- mice. An increase in tissue wet/dry weight ratios was also observed in these organs at 3 h post-burn in WT but not in gammadelta TCR-/- mice. A parallel increase in plasma and small intestine levels of the chemokines macrophage-inflammatory protein-1beta (chemokine ligand 4) and keratinocyte-derived chemokine (CXC chemokine ligand 1) were observed in injured WT mice but not in injured gammadelta TCR-/- mice. Increased activation (CD120b expression) of the circulating gammadelta T cell population was also observed at 3 h post-burn in WT mice. These results indicate the gammadelta T cells, through the production of chemokines, play a central role in the initiation of neutrophil-mediated tissue damage post-burn.

Gammadelta T lymphocytes from cystic fibrosis patients and healthy donors are high TNF-alpha and IFN-gamma-producers in response to Pseudomonas aeruginosa

BACKGROUND

Gammadelta T cells have an important immunoregulatory and effector function through cytokine release. They are involved in the responses to Gram-negative bacterium and in protection of lung epithelium integrity. On the other hand, they have been implicated in airway inflammation.

METHODS

The aim of the present work was to study intracytoplasmic IL-2, IL-4, IFN-gamma and TNF-alpha production by gammadelta and alphabeta T lymphocytes from cystic fibrosis patients and healthy donors in response to Pseudomonas aeruginosa (PA). Flow cytometric detection was performed after peripheral blood mononuclear cells (PBMC) culture with a cytosolic extract from PA and restimulation with phorbol ester plus ionomycine. Proliferative responses, activation markers and receptor usage of gammadelta T cells were also evaluated.

RESULTS

The highest production of cytokine was of TNF-alpha and IFN-gamma, gammadelta being better producers than alphabeta. No differences were found between patients and controls. The Vgamma9delta2 subset of gammadelta T cells was preferentially expanded. CD25 and CD45RO expression by the alphabeta T subset and PBMC proliferative response to PA were defective in cystic fibrosis lymphocytes.

CONCLUSION

Our results support the hypothesis that gammadelta T lymphocytes play an important role in the immune response to PA and in the chronic inflammatory lung reaction in cystic fibrosis patients. They do not confirm the involvement of a supressed Th1 cytokine response in the pathogenesis of this disease.

Mechanisms of immune resolution

Initially after injury, the innate/proinflammatory and some aspects of the acquired immune response are up-regulated to maintain a defense against foreign pathogens, clear tissue debris present at the wound site, and orchestrate aspects of tissue remodeling, cell proliferation and angiogenic process, associated with the wound response. However, for proper wound healing to progress, this initial inflammatory response has to be regulated or shut down so as to allow for the reestablishment of matrix, recellularization, and tissue remodeling. Inability to properly resolve the extent of innate/acquired response at a site of injury can lead to poor wound healing, immune suppression, and recurrent infectious episodes. This review attempts to summarize information on regulatory mechanisms that are thought to be involved in controlling/resolving innate or acquired immune responses so as to provide a framework for use in thinking about the impact these processes and their manipulation may have on wound healing and its potential management.

Macrophages and post-burn immune dysfunction

The activation of a pro-inflammatory cascade after burn injury appears to be important in the development of subsequent immune dysfunction, susceptibility to sepsis and multiple organ failure. Macrophages are major producers of pro-inflammatory mediators and their productive capacity for these mediators is markedly enhanced following thermal injury. Thus, macrophage hyperactivity (as defined by increased productive capacity for pro-inflammatory mediators) appears to be of critical importance in the development of post-burn immune dysfunction. This review will focus on the current state of knowledge with regards to the role of macrophages in the development of post-burn immune dysfunction. Particular areas of discussion include: nitric oxide synthase (NOS) and cyclooxygenase (COX) enzyme systems, macrophages and the T-helper (Th)-1/Th-2 cytokine responses, alterations in macrophages signal transduction and a potential role for gamma/delta T-cells in the development of macrophage hyperactivity following thermal injury. A more comprehensive understanding of the relationship between macrophage activity and post-burn immune dysfunction will hopefully provide the basis for improved therapeutic regimes in the treatment of burn patients.

Direct evidence for interferon-gamma production by effector-memory-type intraepidermal T cells residing at an effector site of immunopathology in fixed drug eruption

Effector-memory T cells are strategically placed to epithelial tissues to provide frontline immune protection against pathogens. Their detrimental effects, however, have been rarely examined because of difficulty in sampling these T cells in pathological settings. Our previous studies suggested persistence of a similar subset of intraepidermal CD8(+) T cells at high frequencies in the lesions of fixed drug eruption, a localized variant of drug-induced dermatoses. In situ activation of this subset resulting in localized epidermal injury can be traced in the lesions after antigen challenge by paired immunohistochemical staining, reverse transcriptase-polymerase chain reaction in situ, and flow cytometry of dispersed cells. Here we show that effector-memory T cells were greatly enriched in these intraepidermal CD8(+) T cells, but not dermal and circulating counterparts, and that they constitutively express an early activation marker CD69 even before challenge. Surprisingly, a large proportion of these T cells expressed immediate effector function as evidenced by the rapid production of high levels of interferon-gamma in situ with much faster kinetics than their counterparts at the mRNA and protein levels after challenge. This was followed by localized epidermal injury. The intracellular cytokine assay ex vivo shows that the great majority of these dispersed T cells produce interferon-gamma. This study provides the first in situ description of the detrimental effects specifically mediated by effector-memory T cells residing at the effector site of immunopathology.

Human V gamma 2V delta 2 T cells augment migration-inhibitory factor secretion and counteract the inhibitory effect of glucocorticoids on IL-1 beta and TNF-alpha production

In immune cells, proinflammatory cytokine gene expression is regulated by glucocorticoids, whereas migration-inhibitory factor (MIF), a pleiotropic cytokine, has the unique property of counteracting the inhibitory effect of glucocorticoids on TNF-alpha and IL-1beta secretion. A few lines of evidence suggest that gammadelta T cells play an important role in immunoregulation. However, it is unknown whether human gammadelta T cells participate in regulating MIF secretion, and how gammadelta T cells, glucocorticoids, and cytokines converge to give a unified physiological response. In this study, we demonstrate that human Vgamma2Vdelta2 T cells augment MIF secretion. Remarkably, these Vgamma2Vdelta2 T cells, functioning similarly to MIF in part, counteracted inhibition of dexamethasone on production of IL-1beta and TNF-alpha. SCID mice reconstituted with human PBMC that were mock depleted of Vdelta2 T cells and repeatedly infected with lethal dose of Escherichia coli had shorter survival time than those reconstituted with PBMC that were depleted of Vdelta2 T cells. Thus, human Vgamma2Vdelta2 T cells are likely to play broad-spectrum roles in immunoregulation and immunopathology by influencing MIF secretion and the immunomodulatory function of glucocorticoids.

Unmodified and phosphorylated prolactin and gamma delta T cell development and function

This manuscript discusses our studies to date concerning the effects of unmodified prolactin (PRL) and phosphorylated PRL on immune function. Most of the discussion refers to effects of changing the ratio of these two forms in maternal PRL on gamma delta T cell development in rat pups in utero, but limited experiments where adult animals have been directly treated are also discussed. The manuscript begins with some general background on gamma delta T cells and the different forms of PRL and then proceeds to a discussion of experimental findings. Results demonstrate that the ratio of unmodified to phosphorylated PRL during rat pregnancy is crucial to normal epidermal gamma delta T cell development in the pup thymus. Elevation of phosphorylated PRL in the dams, by administration of a recombinant molecular mimic of phosphorylated PRL, produces a defect in epidermalgamma delta T cell seeding and subsequent function in the offspring. In contrast, a functional defect is not seen for uterine gamma delta T cells in the offspring, a finding likely reflective of the continued availability of precursors to these cells after the fetal period. Preliminary results from treatment of the NZB/NZW mouse model of lupus with the two forms of PRL suggest opposing effects of unmodified and phosphorylated PRL on one measure of the disease.

Pathological and immunological changes after challenge infection with Pasteurella multocida in naive and immunized calves

Challenge infections of calves with Pasteurella multocida were established to characterize the local inflammatory response and determine the effect of previous exposure to live bacteria on the post-challenge immune response. Experimental infections were established by intratracheal inoculation of P. multocida in both naive calves and calves that had been previously vaccinated with two subcutaneous (s.c.) injections of live bacteria. Histological, immunohistological and cytokine expression studies were performed on bronchoalveolar lavage (BAL) samples, lung parenchymal tissues and lung lymph nodes (LN). In comparison to uninfected control animals in which no lung lesions were observed, a patchy to confluent bronchopneumonia was observed following infection of naive calves, characterized by abscess formation, haemorrhage, oedema and suppurative consolidation. Cellular analysis following infection of naive animals was characterized by an influx of neutrophils in the BAL, with macrophages and dendritic cells observed in the lesion perimeter. A significant increase in the number of CD8(+) blasts expressing MHC (major histocompatibility) II was also observed in the BAL of infected calves. Decreased expression of interleukin (IL)-1 beta and increased expression of IL-8 compared to naive unchallenged controls was apparent in lung LN. In comparison, a more limited pathology was observed in vaccinated animals post-challenge, indicating partial protection conferred by the s.c. immunization with live bacteria. Studies of vaccinated animals showed the presence of bronchial-associated lymphoid tissue (BALT) in the lung tissue and an increase in the number of B-cells and CD4(+) T-cells expressing MHCII in the lung LN after challenge. In contrast to primary infection, there was no significant influx of neutrophils in the BAL. Instead, a population of newly recruited monocytes/macrophages was observed. Increased IL-2 expression and decreased IL-8 expression was observed in the LN, while IL-1 beta expression was not detected. The reduced neutrophil and increase monocyte response in the vaccinated calves may be associated with significant changes in the gamma delta T lymphocyte population in the BAL.

Tumor necrosis factor-alpha negatively regulates airway hyperresponsiveness through gamma-delta T cells

Tumor necrosis factor (TNF)-alpha is a potent cytokine with immunomodulatory, proinflammatory, and pathobiologic activities. Although TNF-alpha is thought to play a role in mediating airway inflammation and airway hyperresponsiveness (AHR), its function is not well defined. TNF-alpha-deficient mice and mice expressing TNF-alpha in their lungs because of a TNF-alpha transgene placed under the control of the surfactant protein (SP)-C promoter (SP-C/TNF-alpha-transgenic mice) were sensitized to ovalbumin (OVA) and subsequently challenged with OVA via the airways; airway function in response to inhaled methacholine was monitored. In the TNF-alpha-deficient mice, AHR was significantly increased over that in controls. In contrast, the transgenic mice failed to develop AHR. In addition, sensitized/ challenged TNF-alpha-deficient mice had significantly increased numbers of eosinophils and higher levels of interleukin (IL)-5 and IL-10 in their bronchoalveolar lavage fluid than were found for control mice. However, in SP-C/TNF-alpha-transgenic mice, both the numbers of eosinophils and levels of IL-5 and IL-10 were significantly lower than in sensitized/challenged transgene-negative mice. gammadelta T cells have been shown to be activated by TNF-alpha and to negatively regulate AHR. Depletion of gammadelta T cells in the TNF-alpha-transgenic mice in the present study increased AHR, whereas depletion of these cells had no significant effect in TNF-alpha-deficient mice. These data indicate that TNF-alpha can negatively modulate airway responsiveness, controlling airway function in allergen-induced AHR through the activation of gammadelta T cells.

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

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

Human gammadelta T cells express a higher TCR/CD3 complex density than alphabeta T cells

The aim of our study was to compare CD3 expression on gammadelta T cells and alphabeta T cells in human patients. The antigen density of TCR and CD3 on both subsets was assessed by a quantitative method in eight patients. In parallel, we developed and validated a reliable direct tricolor staining protocol that we tested on samples from hospitalized and healthy individuals (n = 60). Our results demonstrate that human gammadelta T cells constitutively express approximately twofold more of the TCR/CD3 complex than alphabeta T cells. We suggest that this enhanced expression of the TCR/CD3 complex could contribute to the higher reactivity of gammadelta T cells compared to alphabeta T cells. These clinical laboratory results confirm the fundamental data described elsewhere. gammadelta T cells deserve further clinical investigations to understand their precise role in human immunity.

Both gamma delta T cells and NK cells inhibit the engraftment of xenogeneic rat bone marrow cells and the induction of xenograft tolerance in mice

In murine allogeneic bone marrow transplantation recipients, treatment of the hosts with a nonmyeloablative regimen, including depleting anti-CD4 and anti-CD8 mAbs, allows establishment of long-term mixed chimerism and donor-specific tolerance. However, in the xenogeneic rat-to-mouse combination, additional anti-Thy1.2 and anti-NK1.1 mAbs are required. We have now attempted to identify the xenoresistant mouse cell populations that are targeted by anti-NK1.1 and anti-Thy1.2 mAbs. C57BL/6 (B6) wild-type, B6 TCRbeta(-/-), and B6 TCRdelta(-/-) mice received anti-CD4 and anti-CD8 mAbs, followed by 3 Gy of whole body irradiation, 7 Gy of thymic irradiation, and transplantation of T cell-depleted rat bone marrow cells. Anti-NK1.1 and anti-Thy1.2 mAbs were additionally administered to some groups. Increased rat chimerism was observed in TCRdelta(-/-) mice treated with anti-CD4, anti-CD8, and anti-NK1.1 mAbs compared with similarly treated TCRbeta(-/-) mice. In TCRbeta(-/-) mice, but not in TCR delta(-/-) mice, donor chimerism was increased by treatment with anti-Thy1.2 mAb, indicating that CD4(-)CD8(-)TCRgammadelta(+)Thy1. 2(+)NK1.1(-) cells (gammadelta T cells) are involved in the rejection of rat marrow. In addition, chimerism was enhanced in both TCRbeta(-/-) and TCRdelta(-/-) mice treated with anti-CD4, anti-CD8, and anti-Thy1.2 mAbs by the addition of anti-NK1.1 mAb to the conditioning regimen. Donor-specific skin graft prolongation was enhanced by anti-Thy1.2 and anti-NK1.1 mAbs in TCRdelta(-/-) mice. Therefore, in addition to CD4 and CD8 T cells, gammadelta T cells and NK cells play a role in resisting engraftment of rat marrow and the induction of xenograft tolerance in mice.

Gamma delta-T cells are critical for survival and early proinflammatory cytokine gene expression during murine Klebsiella pneumonia

Although cells of the innate inflammatory response, such as macrophages and neutrophils, have been extensively studied in the arena of Gram-negative bacterial pneumonia, a role for T cells remains unknown. To study the role of specific T cell populations in bacterial pneumonia, mice deleted of their TCR beta- and/or delta-chain were intratracheally inoculated with Klebsiella pneumoniae. Gamma delta T cell knockout mice displayed increased mortality at both early and late time points. In contrast, mice specifically lacking only alpha beta-T cells were no more susceptible than wild-type mice. Pulmonary bacterial clearance in gamma delta-T cell knockout mice was unimpaired. Interestingly, these mice displayed increased peripheral blood dissemination. Rapid up-regulation of IFN-gamma and TNF-alpha gene expression, critical during bacterial infections, was markedly impaired in lung and liver tissue from gamma delta-T cell-deficient mice 24 h postinfection. The increased peripheral blood bacterial dissemination correlated with impaired hepatic bacterial clearance following pulmonary infection and increased hepatic injury as measured by plasma aspartate aminotransferase activity. Combined, these data suggest that mice lacking gamma delta-T cells have an impaired ability to resolve disseminated bacterial infections subsequent to the initial pulmonary infection. These data indicate that gamma delta-T cells comprise a critical component of the acute inflammatory response toward extracellular Gram-negative bacterial infections and are vital for the early production of the proinflammatory cytokines IFN-gamma and TNF-alpha.

Role of T cells and cytokines in fatal and resolving experimental babesiosis: protection in TNFRp55-/- mice infected with the human Babesia WA1 parasite

We characterized the cytokine response and T-cell requirements of mice infected with the intraerythrocytic parasites Babesia microti and WA1. WA1 infections were fatal, whereas B. microti infections were resolved. We measured production of tumor necrosis factor (TNF)-alpha, interferon-gamma, interleukin (IL)-10, and IL-4 by splenic CD4+, CD8+, and gammadelta+ T cells using flow cytometry. WA1 inoculation stimulated TNF-alpha production, whereas resolving B. microti infections were characterized by increased IL-10 and IL-4. The role of TNF-alpha in WA1 infections was further investigated by inoculating TNFRp55-/- mice with a lethal dose of WA1. A survival rate of 90% in the TNFRp55-/- mice indicated that a disruption in the TNF-alpha pathway abrogated the pathologic mechanism of WA1. Inoculation of WA1 into CD4-/- and CD8-/- mice resulted in survival rates of 60% and 78%, respectively, whereas WA1 infection in gammadelta-/- and control mice was fatal. These results suggest that CD8+ T cells may contribute to the WA1-associated disease. Babesia-infected CD4-/- mice experienced a longer duration of parasitemia, indicating that CD4+ T cells participate in parasite elimination. These studies demonstrate differences in immune responses during fatal or resolving Babesia infections, and they identify TNF-alpha as an important mediator of the WA1-associated pathogenesis.

[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.

Expression of toll-like receptor 2 on gamma delta T cells bearing invariant V gamma 6/V delta 1 induced by Escherichia coli infection in mice

We recently reported that the number of gamma delta T cells was increased after infection with Escherichia coli in C3H/HeN mice. We here showed that an i.p. injection with native lipid A derived from E. coli induced an increase of gamma delta T cells in the peritoneal cavity of LPS-responsive C3H/HeN mice and, albeit to a lesser degree, also in LPS-hyporesponsive C3H/HeJ mice. The purified gamma delta T cells from C3H/HeN and C3H/HeJ mice expressed a canonical TCR repertoire encoded by V gamma 6-J gamma 1/V delta 1-D delta 2-J delta 2 gene segments and proliferated in response to the native lipid A derived from E. coli in a TCR-independent manner. The lipid A-reactive gamma delta T cells bearing canonical V gamma 6/V delta 1 expressed Toll-like receptor (TLR) 2 mRNA, while TLR4 mRNA was undetectable. Treatment with a TLR2 anti-sense oligonucleotide resulted in hyporesponsiveness of the gamma delta T cells to the native lipid A. TLR2-deficient mice showed an impaired increase of the gamma delta T cells following injection of native lipid A. These results suggest that TLR2 is involved in the activation of canonical V gamma 6/V delta 1 T cells by native E. coli lipid A.

Human uvula: characterization of resident leukocytes and local cytokine production

Upper airway infections often lead to macroscopic changes in the architecture of the uvula. Using immunomorphometric analysis, we investigated the frequency and distribution of immune cells and of cytokine-producing cells in uvular samples. Tissue macrophages, alphabeta T cells, gammadelta T cells, and B cells were, in declining order, the main cell populations. Gammadelta T cells and B cells exhibited reciprocal localization, with almost all gammadelta T cells residing in the vicinity of the epithelium, and all B cells in the glandular area. The presence of cells expressing the suppressor phenotype CD8+CD28- alphabeta T cells is suggested. Fifteen to twenty-five percent of the immune cells expressed the down-regulatory cytokine tumor growth factor beta. Most macrophages were located subepithelially, in the vicinity of the basal lamina. The composition and cytokine profile of leukocytes in the tissue suggest that the uvula may be a site, additional to the jejunal mucosa, for induction of mucosal tolerance to inhaled and ingested antigens. Concomitantly, the uvula appears to be protected from invasion of microbial pathogens by a subepithelial barrier of macrophages and gammadelta T cells.

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.

Decreased expression of FcgammaRIII (CD16) by gammadelta T cells in patients with rheumatoid arthritis

Some gammadelta T cells express a receptor for the Fc portion of immunoglobulin G (FcgammaRIII - CD16). The relevance of this Fc receptor to gammadelta T-cell function is at present unclear. Our previous studies have shown that gammadelta T cells express activation markers in patients with rheumatoid arthritis (RA). In this study we have examined the relative proportions of CD16+ gammadelta T cells in the blood and synovial fluid of these patients compared with control blood. CD16+ gammadelta T cells from RA patients were significantly reduced in synovial fluid compared with the circulation. That this was due to blocking of antibody binding to CD16 was unlikely as treatment of blood gammadelta T cells with RA synovial fluid (known to contain immune complexes) failed to alter expression of CD16. Treatment of blood gammadelta T cells with phytohaemagglutinin in vitro, resulted in a time-dependent decrease in expression of CD16, with a concomitant increase in expression of human leucocyte antigen-DR, at the single cell level. We conclude that expression of CD16 by gammadelta T cells is lost in the synovial compartment as the result of activation.

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

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

Insufficient resistance of trehalose-6,6-dimycolate-treated T-cell receptor delta gene mutant (TCR delta-/-) mice against influenza virus infection

Normal mice inoculated intravenously with 50 microg trehalose-6,6'-dimycolate, a glycolipid component of the cell wall of Mycobacterium, in an oil-in-water emulsion (TDM emulsion) acquired a high resistance to intranasal lethal infection of an influenza virus. In contrast, TDM emulsion-treated T-cell receptor delta gene mutant (TCR delta-/-) mice acquired insufficient resistance against the lethal influenza virus infection. The patterns of insufficient resistance were identical to the results obtained previously with mice which were depleted of T-lymphocytes bearing gammadelta T-cell receptors (gammadelta T-cells) by in vivo administration of anti-gammadelta T-cell receptor monoclonal antibody (Hoq et al, J. Gen. Virol. 78: 1597-1603, 1997). These results strongly suggest that the gammadelta T-cells play an important non-specific role in resistance against influenza virus infection.

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

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

Regulatory Role of Peritoneal NK1.1+αβ T Cells in IL-12 Production During Salmonella Infection

NK1.1+αβ T cells emerge in the peritoneal cavity after an i.p. infection with Salmonella choleraesuis in mice. To elucidate the role of the NK1.1+αβ T cells during murine salmonellosis, mice lacking NK1.1+αβ T cells by disruption of TCRβ (TCRβ−/−), β2m (β2m−/−), or Jα281 (Jα281−/−) gene were i.p. inoculated with S. choleraesuis. The peritoneal exudate T cells in wild type (wt) mice on day 3 after infection produced IL-4 upon TCRαβ stimulation, whereas those in TCRβ−/−, β2m−/−, or Jα281−/− mice showed no IL-4 production upon the stimulation, indicating that NK1.1+αβ T cells are the main source of IL-4 production at the early phase of Salmonella infection. Neutralization of endogenous IL-4 by administration of anti-IL-4 mAb to wt mice reduced the number of Salmonella accompanied by increased IL-12 production by macrophages after Salmonella infection. The IL-12 production by the peritoneal macrophages was significantly augmented in mice lacking NK1.1+αβ T cells after Salmonella infection accompanied by increased serum IFN-γ level. The aberrantly increased IL-12 production in infected TCRβ−/− or Jα281−/− mice was suppressed by adoptive transfer of T cells containing NK1.1+αβ T cells but not by the transfer of T cells depleted of NK1.1+αβ T cells or T cells from Jα281−/− mice. Taken together, it is suggested that NK1.1+αβ T cells eliciting IL-4 have a regulatory function in the IL-12 production by macrophages at the early phase of Salmonella infection.

Plasticity of Immune Responses Suppressing Parasitemia During Acute Plasmodium chabaudi Malaria

γδ T cells have a crucial role in cell-mediated immunity (CMI) against P. chabaudi malaria, but δ-chain knockout (KO) (δo/o) mice and mice depleted of γδ T cells with mAb cure this infection. To address the question of why mice deficient in γδ T cells resolve P. chabaudi infections, we immunized δo/o mice by infection with viable blood-stage parasites. Sera from infection-immunized mice were tested for their ability to protect JHo/o, δo/o double KO mice passively against P. chabaudi challenge infection. The onset of parasitemia was significantly delayed in mice receiving immune sera, compared with saline or uninfected serum controls. Immune sera were then fractionated into Ig-rich and Ig-depleted fractions by HPLC on a protein G column. Double KO mice were passively immunized with either fraction and challenged with P. chabaudi. The onset of parasitemia was significantly delayed in recipients of the Ig-rich fraction compared with recipients of the Ig-poor fraction of immune sera. We conclude that δo/o mice, which are unable to activate CMI against the parasite, suppress P. chabaudi infection by a redundant Ab-mediated process.

Macrophage Control of Herpes Simplex Virus Type 1 Replication in the Peripheral Nervous System

After corneal infection, herpes simplex virus type 1 (HSV-1) invades sensory neurons with cell bodies in the trigeminal ganglion (TG), replicates briefly, and then establishes a latent infection in these neurons. HSV-1 replication in the TG can be detected as early as 2 days after corneal infection, reaches peak titers by 3–5 days after infection, and is undetectable by 7–10 days. During the period of HSV-1 replication, macrophages and γδ TCR+ T lymphocytes infiltrate the TG, and TNF-α, IFN-γ, the inducible nitric oxide synthase (iNOS) enzyme, and IL-12 are expressed. TNF-α, IFN-γ, and the iNOS product nitric oxide (NO) all inhibit HSV-1 replication in vitro. Macrophage and γδ TCR+ T cell depletion studies demonstrated that macrophages are the main source of TNF-α and iNOS, whereas γδ TCR+ T cells produce IFN-γ. Macrophage depletion, aminoguanidine inhibition of iNOS, and neutralization of TNF-α or IFN-γ all individually and synergistically increased HSV-1 titers in the TG after HSV-1 corneal infection. Moreover, individually depleting macrophages or neutralizing TNF-α or IFN-γ markedly reduced the accumulation of both macrophages and γδ TCR+ T cells in the TG. Our findings establish that after primary HSV-1 infection, the bulk of virus replication in the sensory ganglia is controlled by macrophages and γδ TCR+ T lymphocytes through their production of antiviral molecules TNF-α, NO, and IFN-γ. Our findings also strongly suggest that cross-regulation between these two cell types is necessary for their accumulation and function in the infected TG.

Gamma delta intraepithelial lymphocytes drive tumor necrosis factor-alpha responsiveness to intestinal iron challenge: relevance to hemochromatosis

The dependence of intestinal epithelial cell (IEC) growth and differentiation on intraepithelial lymphocytes (IELs) expressing the gamma/delta (gamma delta) T-cell receptor (TCR), suggested a potential role for gamma delta + IELs in the regulation of iron absorption. We therefore examined the levels of hepatic iron and the IEL cytokine responses in C57BL/6J control and class I and TCR knockout lines (placed on a C57BL/6J genetic background) following the administration of supplemental dietary iron. The highest level of liver iron was found in the beta 2-microglobulin knockout (beta 2m-/-) mice followed by the TCR-delta knockout (TCR delta-/-) animals. TCR-alpha knockout (TCR alpha-/-) and control animals did not differ in their iron levels. Liver iron loading correlated inversely with the ability of the mice to generate an IEL tumor necrosis factor (TNF)-alpha response. These observations suggest a model in which IEC iron loading is communicated to IELs via the HFE class I protein. The result of this communication is the initiation of TNF-alpha release by gamma delta + IELs (sustained by macrophages and dendritic cells) contributing to the upregulation of ferritin expression and possibly to the normal maintenance of the IEC apoptotic pathway.

Lipid A directly inhibits IL-4 production by murine Th2 cells but does not inhibit IFN-gamma production by Th1 cells

Lipopolysaccharide (LPS) is known to be an immunopotentiator but its effect on cytokine production by Th1 and Th2 cells is unknown. We found that high amounts of LPS, its lipid A moiety, and a lipid A analog all induced a decrease in IL-4 production and an increase in IFN-gamma production when given to keyhole limpet hemocyanin (KLH)-restimulated lymph node cells prepared from KLH-primed mice. Lipid A was similarly found to inhibit IL-4 production by purified CD4+ T cells and Th2 clones activated with immobilized anti-CD3epsilon and anti-CD28 antibodies, suggesting that the inhibition is not indirectly mediated through effects on antigen-presenting cells. No inhibitory effect of lipid A was observed on IFN-gamma production by a Th1 clone. Production of both IL-4 by the Th2 clones and IFN-gamma by the Th1 clone were inhibited by the immunosuppressive agent cyclosporin A. These findings indicate that lipid A can directly inhibit IL-4 production by CD4+ T cells without inhibiting the production of IFN-gamma. Lipid A may therefore become a useful tool to study the intracellular events that differentiate Th1 and Th2 cells.

Why did your mother reject you? Immunogenetic determinants of the response to environmental selective pressure expressed at the uterine level

PROBLEM

Maternal "rejection" of the implanted conceptus is considered to account for a significant proportion of miscarriages (abortions) in both humans and animals. Our understanding of mechanisms has been limited, and hence, explanations for nonrejection have remained largely speculative. Losses, when they occur, could represent either random accidental failure of protective mechanisms or a more purposeful discrimination.

METHOD OF STUDY

An analysis of the most recent data.

RESULTS AND CONCLUSIONS

The embryo is most akin to a parasite, and pregnancy is most akin to a host-parasite interaction. If one excludes chromosome abnormalities in the embryo as a cause of death, activation of coagulation mechanisms, leading to vasculitis affecting the maternal blood supply to the implanted embryo, appears to represent a major loss-causing mechanisms--a form of ischemic autoamputation. Proinflammatory T-helper (Th) 1-type cytokines trigger this process via upregulation of a novel prothrombinase, fgl2. Th2/3 cytokines, such as interleukin (IL)-4, IL-10, and transforming growth factor (TGF)-beta 2, may antagonize the processes involved. Cytokine balance is determined by the genetics of the mother, which regulate her response to stress; endotoxin (LPS); and paternal antigens, selectively expressed on the trophoblast of the embryo, via imprinting. Based on studies in abortion-prone mice, where immunity to paternal alloantigens prevents loss, three distinct gene products in the embryo are proposed to determine the cytokine response to maternal lymphomyeloid cells in the uterus.