Apoptosis of Fashigh CD4+ synovial T cells by borrelia-reactive Fas-ligand(high) gamma delta T cells in Lyme arthritis

γδ T cells: origin and fate, subsets, diseases and immunotherapy

The intricacy of diseases, shaped by intrinsic processes like immune system exhaustion and hyperactivation, highlights the potential of immune renormalization as a promising strategy in disease treatment. In recent years, our primary focus has centered on γδ T cell-based immunotherapy, particularly pioneering the use of allogeneic Vδ2+ γδ T cells for treating late-stage solid tumors and tuberculosis patients. However, we recognize untapped potential and optimization opportunities to fully harness γδ T cell effector functions in immunotherapy. This review aims to thoroughly examine γδ T cell immunology and its role in diseases. Initially, we elucidate functional differences between γδ T cells and their αβ T cell counterparts. We also provide an overview of major milestones in γδ T cell research since their discovery in 1984. Furthermore, we delve into the intricate biological processes governing their origin, development, fate decisions, and T cell receptor (TCR) rearrangement within the thymus. By examining the mechanisms underlying the anti-tumor functions of distinct γδ T cell subtypes based on γδTCR structure or cytokine release, we emphasize the importance of accurate subtyping in understanding γδ T cell function. We also explore the microenvironment-dependent functions of γδ T cell subsets, particularly in infectious diseases, autoimmune conditions, hematological malignancies, and solid tumors. Finally, we propose future strategies for utilizing allogeneic γδ T cells in tumor immunotherapy. Through this comprehensive review, we aim to provide readers with a holistic understanding of the molecular fundamentals and translational research frontiers of γδ T cells, ultimately contributing to further advancements in harnessing the therapeutic potential of γδ T cells.

Cell-Mediated Cytotoxicity in Lyme Arthritis

OBJECTIVE

Obliterative microvascular lesions are found in the synovial tissue of ~50% of patients with post-antibiotic Lyme arthritis (LA) and correlate with autoantibodies to certain vascular antigens. In this study, we identified lymphocytes with cytotoxic potential that may also mediate this feature of synovial pathology.

METHODS

The cytotoxic potential of lymphocytes and their T cell receptor (TCR) Vβ gene usage were determined using samples of peripheral blood mononuclear cells (PBMCs) and synovial fluid mononuclear cells (SFMCs) from patients with antibiotic-responsive or post-antibiotic LA. Cell phenotypes were analyzed using flow cytometry and intracellular cytokine staining. Immunohistochemistry was performed on post-antibiotic synovial tissue samples.

RESULTS

In SFMC and PBMC samples, the percentages of CD8+ T cells and double-negative T cells (primarily γδ T cells) were greater among 22 patients with post-antibiotic LA than in 14 patients with antibiotic-responsive LA. Moreover, CD8+ T cells and γδ T cells often expressed cytotoxic mediators, granzyme A/granzyme B, and perforin. The same 3 TCR Vβ segments were over-represented in both CD4+ T cells and CD8+ T cells in SFMC samples from post-antibiotic LA patients. In synovial tissue samples from 3 patients with post-antibiotic LA, CD8+ T cells intermixed with CD4+ T cells were seen around blood vessels, and 2 patients with microvascular damage had autoantibodies to vascular-associated antigens. One of these 2 patients, the one in whom cytotoxicity appeared to be active, had complement (C5b-9) deposition on obliterated vessels. Very few natural killer cells or γδ T cells were seen.

CONCLUSION

We propose that CD8+ T cell-mediated cytotoxicity, CD4+ T cell help, autoantibodies to vascular antigens, and complement deposition may each have a role in microvasculature damage in post-antibiotic LA.

Regulation of Synovial γδ T Cell Ligand Expression by Mitochondrial Reactive Oxygen Species and Gasdermin-D

γδ T cells reside at mucosal and epithelial barriers, and they often accumulate at sites of inflammation, both infectious and autoimmune, as well as in certain tumors. However, progress in understanding their function is considerably hampered by a lack of full understanding of the ligands recognized by TCR-γδ and how expression of these ligands is regulated. We recently developed a soluble human TCR-γδ (Vγ9Vδ1) tetramer from a synovial γδ T cell clone of a Lyme arthritis patient and observed that it stains monocytes activated by Borrelia burgdorferi. Those findings are extended in the current study to further examine the physiological regulation of ligand expression on monocytes. The TCR-γδ ligand is induced by a variety of TLR agonists and requires NF-κB activation. Of particular interest is that ligand expression also requires caspase activation of the inflammasome and is dependent on active metabolism, mitochondrial reactive oxygen species, and activation of gasdermin-D. Consistent with these observations, the TCR-γδ ligand is expressed by a subset of metabolically active CD14+CD16+ monocytes and colocalizes intracellularly with mitochondria. The findings suggest a model in which synovial γδ T cell ligand is a self-antigen whose surface expression is increased by inflammatory conditions and mitochondrial stress.

Differentiation and functional plasticity of gamma-delta (γδ) T cells under homeostatic and disease conditions

Gamma-delta (γδ) T cells are a heterogeneous population of immune cells, which constitute <5% of total T cells in mice lymphoid tissue and human peripheral blood. However, they comprise a higher proportion of T cells in the epithelial and mucosal barrier, where they perform immune functions, help in tissue repair, and maintaining homeostasis. These tissues resident γδ T cells possess properties of innate and adaptive immune cells which enables them to perform a variety of functions during homeostasis and disease. Emerging data suggest the involvement of γδ T cells during transplant rejection and survival. Interestingly, several functions of γδ T cells can be modulated through their interaction with other immune cells. This review provides an overview of development, differentiation plasticity into regulatory and effector phenotypes of γδ T cells during homeostasis and various diseases.

Differential skewing of donor-unrestricted and γδ T cell repertoires in tuberculosis-infected human lungs

Unconventional T cells that recognize mycobacterial antigens are of great interest as potential vaccine targets against tuberculosis (TB). This includes donor-unrestricted T cells (DURTs), such as mucosa-associated invariant T cells (MAITs), CD1-restricted T cells, and γδ T cells. We exploited the distinctive nature of DURTs and γδ T cell receptors (TCRs) to investigate the involvement of these T cells during TB in the human lung by global TCR sequencing. Making use of surgical lung resections, we investigated the distribution, frequency, and characteristics of TCRs in lung tissue and matched blood from individuals infected with TB. Despite depletion of MAITs and certain CD1-restricted T cells from the blood, we found that the DURT repertoire was well preserved in the lungs, irrespective of disease status or HIV coinfection. The TCRδ repertoire, in contrast, was highly skewed in the lungs, where it was dominated by Vδ1 and distinguished by highly localized clonal expansions, consistent with the nonrecirculating lung-resident γδ T cell population. These data show that repertoire sequencing is a powerful tool for tracking T cell subsets during disease.

Detection of Cell Surface Ligands for Human Synovial γδ T Cells

Lack of understanding of the nature and physiological regulation of γδ T cell ligands has considerably hampered full understanding of the function of these cells. We developed an unbiased approach to identify human γδ T cells ligands by the production of a soluble TCR-γδ (sTCR-γδ) tetramer from a synovial Vδ1 γδ T cell clone from a Lyme arthritis patient. The sTCR-γδ was used in flow cytometry to initially define the spectrum of ligand expression by both human tumor cell lines and certain human primary cells. Analysis of diverse tumor cell lines revealed high ligand expression on several of epithelial or fibroblast origin, whereas those of hematopoietic origin were largely devoid of ligand. This allowed a bioinformatics-based identification of candidate ligands using RNAseq data from each tumor line. We further observed that whereas fresh monocytes and T cells expressed low to negligible levels of TCR-γδ ligands, activation of these cells resulted in upregulation of surface ligand expression. Ligand upregulation on monocytes was partly dependent upon IL-1β. The sTCR-γδ tetramer was then used to bind candidate ligands from lysates of activated monocytes and analyzed by mass spectrometry. Surface TCR-γδ ligand was eliminated by treatment with trypsin or removal of glycosaminoglycans, and also suppressed by inhibition of endoplasmic reticulum-Golgi transport. Of particular interest was that inhibition of glycolysis also blocked TCR-γδ ligand expression. These findings demonstrate the spectrum of ligand(s) expression for human synovial Vδ1 γδ T cells as well as the physiology that regulates their expression.

Distinct phenotype and function of circulating Vδ1+ and Vδ2+ γδT-cells in acute and chronic hepatitis B

Hepatitis B virus (HBV) persists with global and virus-specific T-cell dysfunction, without T-cell based correlates of outcomes. To determine if γδT-cells are altered in HBV infection relative to clinical status, we examined the frequency, phenotype and function of peripheral blood Vδ1⁺ and Vδ2⁺γδT-cells by multi-parameter cytometry in a clinically diverse North American cohort of chronic hepatitis B (CHB), acute hepatitis B (AHB) and uninfected control subjects. We show that circulating γδT-cells were comprised predominantly of CD3^hiCD4^- Vδ2⁺γδT-cells with frequencies that were 2–3 fold higher among Asian than non-Asian Americans and inversely correlated with age, but without differences between CHB, AHB and control subjects. However, compared to control subjects, CHB was associated with increased Tbet^hiEomes^dim phenotype in Vδ2⁺γδT-cells whereas AHB was associated with increased Tbet^hiEomes^dim phenotype in Vδ1⁺γδT-cells, with significant correlations between Tbet/Eomes expression in γδT-cells with their expression of NK and T-cell activation and regulatory markers. As for effector functions, IFNγ/TNF responses to phosphoantigens or PMA/Ionomycin in Vδ2⁺γδT-cells were weaker in AHB but preserved in CHB, without significant differences for Vδ1⁺γδT-cells. Furthermore, early IFNγ/TNF responses in Vδ2⁺ γδT-cells to brief PMA/Ionomycin stimulation correlated inversely with serum ALT but not HBV DNA. Accordingly, IFNγ/TNF responses in Vδ2⁺γδT-cells were weaker in patients with CHB with hepatitis flare compared to those without hepatitis flares, and this functional deficit persisted beyond clinical resolution of CHB flare. We conclude that circulating γδT-cells show distinct activation and differentiatiation in acute and chronic HBV infection as part of lymphoid stress surveillance with potential role in clinical outcomes.

We examined circulating γδT-cells in a North American cohort with chronic hepatitis B (CHB) and acute hepatitis B (AHB) compared to uninfected control subjects. While frequencies and composition of circulating γδT-cells were preserved in AHB and CHB, γδT-cells showed distinct and innate phenotypes based on the expression of Tbet/Eomes in association with various NK/T-cell markers. Notably, IFNγ/TNF responses to phosphoantigens and PMA/Ionomycin were preserved in CHB, but weaker in AHB compared to uninfected control subjects, in association with NKG2A/CD94 but not PD1. Furthermore, early IFNγ/TNF responses in Vδ2⁺ γδT-cells to brief PMA/Ionomycin stimulation showed significant inverse correlations with serum alanine aminotransferase, a measure of hepatocellular injury, and were persistently deficient in CHB subjects with hepatitis flare compared to those without such flares. Finally, Vδ2⁺ γδT-cells were significantly enriched for Tbet^hiEomes^dim phenotype in associations with their expression of NK and T-cell activation and regulatory markers, suggesting a role for Tbet in γδT-cell differentiation and function. We conclude that circulating γδT-cells show distinct activation and differentiation in acute and chronic HBV infection as part of lymphoid stress surveillance with potential role in clinical outcomes.

Recasting Human Vδ1 Lymphocytes in an Adaptive Role

γδ T cells are unconventional lymphocytes commonly described as 'innate-like' in function, which can respond in both a T cell receptor (TCR)-independent and also major histocompatibility complex (MHC)-unrestricted TCR-dependent manner. While the relative importance of TCR recognition had remained unclear, recent studies revealed that human Vδ1 T cells display unexpected parallels with adaptive αβ T cells. Vδ1 T cells undergo profound and highly focussed clonal expansion from an initially diverse and private TCR repertoire, most likely in response to specific immune challenges. Concomitantly, they differentiate from a Vδ1 T cell naïve (Tnaïve) to a Vδ1 T cell effector (Teffector) phenotype, marked by the downregulation of lymphoid homing receptors and upregulation of peripheral homing receptors and effector markers. This suggests that an adaptive paradigm applies to Vδ1 T cells, likely involving TCR-dependent but MHC-unrestricted responses to microbial and non-microbial challenges.

IL-10 Deficiency Reveals a Role for TLR2-Dependent Bystander Activation of T Cells in Lyme Arthritis

T cells predominate the immune responses in the synovial fluid of patients with persistent Lyme arthritis; however, their role in Lyme disease remains poorly defined. Using a murine model of persistent Lyme arthritis, we observed that bystander activation of CD4+ and CD8+ T cells leads to arthritis-promoting IFN-γ, similar to the inflammatory environment seen in the synovial tissue of patients with posttreatment Lyme disease. TCR transgenic mice containing monoclonal specificity toward non-Borrelia epitopes confirmed that bystander T cell activation was responsible for disease development. The microbial pattern recognition receptor TLR2 was upregulated on T cells following infection, implicating it as marker of bystander T cell activation. In fact, T cell-intrinsic expression of TLR2 contributed to IFN-γ production and arthritis, providing a mechanism for microbial-induced bystander T cell activation during infection. The IL-10-deficient mouse reveals a novel TLR2-intrinsic role for T cells in Lyme arthritis, with potentially broad application to immune pathogenesis.

Necroptosis of Dendritic Cells Promotes Activation of γδ T Cells

γδ T cells function at the interface between innate and adaptive immunity and have well-demonstrated roles in response to infection, autoimmunity and tumors. A common characteristic of these seemingly disparate conditions may be cellular stress or death. However, the conditions under which ligands for γδ T cells are induced or exposed remain largely undefined. We observed that induction of necroptosis of murine or human dendritic cells (DC) by inhibition of caspase activity paradoxically augments their ability to activate γδ T cells. Furthermore, upregulation of the stabilizer of caspase-8 activity, c-FLIP, by IL-4, not only greatly reduced the susceptibility of DC to necroptosis, but also considerably decreased their ability to activate γδ T cells. Collectively, these findings suggest that the induction of necroptosis in DC upregulates or exposes the expression of γδ T cell ligands, and they support the view that γδ T cells function in the immune surveillance of cell stress.

γδ T Cells Play a Protective Role in Chikungunya Virus-Induced Disease

Chikungunya virus (CHIKV) is an alphavirus responsible for causing epidemic outbreaks of polyarthralgia in humans. Because CHIKV is initially introduced via the skin, where γδ T cells are prevalent, we evaluated the response of these cells to CHIKV infection. CHIKV infection led to a significant increase in γδ T cells in the infected foot and draining lymph node that was associated with the production of proinflammatory cytokines and chemokines in C57BL/6J mice. γδ T cell(-/-) mice demonstrated exacerbated CHIKV disease characterized by less weight gain and greater foot swelling than occurred in wild-type mice, as well as a transient increase in monocytes and altered cytokine/chemokine expression in the foot. Histologically, γδ T cell(-/-) mice had increased inflammation-mediated oxidative damage in the ipsilateral foot and ankle joint compared to wild-type mice which was independent of differences in CHIKV replication. These results suggest that γδ T cells play a protective role in limiting the CHIKV-induced inflammatory response and subsequent tissue and joint damage.

IMPORTANCE

Recent epidemics, including the 2004 to 2007 outbreak and the spread of CHIKV to naive populations in the Caribbean and Central and South America with resultant cases imported into the United States, have highlighted the capacity of CHIKV to cause explosive epidemics where the virus can spread to millions of people and rapidly move into new areas. These studies identified γδ T cells as important to both recruitment of key inflammatory cell populations and dampening the tissue injury due to oxidative stress. Given the importance of these cells in the early response to CHIKV, this information may inform the development of CHIKV vaccines and therapeutics.

γδ T Cells and dendritic cells in refractory Lyme arthritis

Lyme disease is a multisystem infection transmitted by tick vectors with an incidence of up to 300,000 individuals/yr in the United States. The primary treatments are oral or i.v. antibiotics. Despite treatment, some individuals do not recover and have prolonged symptoms affecting multiple organs, including the nervous system and connective tissues. Inflammatory arthritis is a common symptom associated with Lyme pathology. In the past decades, γδ T cells have emerged as candidates that contribute to the transition from innate to adaptive responses. These cells are also differentially regulated within the synovia of patients affected by RLA. Here, we review and discuss potential cellular mechanisms involving γδ T cells and DCs in RLA. TLR signaling and antigen processing and presentation will be the key concepts that we review in aid of understanding the impact of γδ T cells in RLA.

Phagosomal TLR signaling upon Borrelia burgdorferi infection

Internalization and degradation of live Bb within phagosomal compartments of monocytes, macrophages and dendritic cells (DCs), allows for the release of lipoproteins, nucleic acids and other microbial products, triggering a broad and robust inflammatory response. Toll-like receptors (TLRs) are key players in the recognition of spirochetal ligands from whole viable organisms (i.e., vita-PAMPs). Herein we will review the role of endosomal TLRs in the response to the Lyme disease spirochete.

Comparative biology of γδ T cell function in humans, mice, and domestic animals

γδ T cells are a functionally heterogeneous population and contribute to many early immune responses. The majority of their activity is described in humans and mice, but the immune systems of all jawed vertebrates include the γδ T cell lineage. Although some aspects of γδ T cells vary between species, critical roles in early immune responses are often conserved. Common features of γδ T cells include innate receptor expression, antigen presentation, cytotoxicity, and cytokine production. Herein we compare studies describing these conserved γδ T cell functions and other, potentially unique, functions. γδ T cells are well documented for their potential immunotherapeutic properties; however, these proposed therapies are often focused on human diseases and the mouse models thereof. This review consolidates some of these studies with those in other animals to provide a consensus for the current understanding of γδ T cell function across species.

Localized production of IL-10 suppresses early inflammatory cell infiltration and subsequent development of IFN-γ-mediated Lyme arthritis

IL-10 is a nonredundant inflammatory modulator that suppresses arthritis development in Borrelia burgdorferi-infected mice. Infected C57BL/6 (B6) IL-10(-/-) mice were previously found to have a prolonged IFN-inducible response in joint tissue. Infection of B6 IL-10 reporter mice identified macrophages and CD4(+) T cells as the primary sources of IL-10 in the infected joint tissue, suggesting that early local production of IL-10 dampened the proarthritic IFN response. Treatment of B6 IL-10(-/-) mice with anti-IFN-γ reduced the increase in arthritis severity and suppressed IFN-inducible transcripts to wild-type levels, thereby linking dysregulation of IFN-γ to disease in the B6 IL-10(-/-) mouse. Arthritis in B6 IL-10(-/-) mice was associated with elevated numbers of NK cell, NKT cell, α/β T cell, and macrophage infiltration of the infected joint. FACS lineage sorting revealed NK cells and CD4(+) T cells as sources of IFN-γ in the joint tissue of B6 IL-10(-/-) mice. These findings suggest the presence of a positive-feedback loop in the joint tissue of infected B6 IL-10(-/-) mice, in which production of inflammatory chemokines, infiltration of IFN-γ-producing cells, and additional production of inflammatory cytokines result in arthritis. This mechanism of arthritis is in contrast to that seen in C3H/He mice, in which arthritis development is linked to transient production of type I IFN and develops independently of IFN-γ. Due to the sustained IFN response driven by NK cells and T cells, we propose the B6 IL-10(-/-) mouse as a potential model to study the persistent arthritis observed in some human Lyme disease patients.

Increased caspase activity primes human Lyme arthritis synovial γδ T cells for proliferation and death

γδ T cells function between the innate and adaptive immune responses, promoting antigen-presenting cell function and manifesting cytolytic activity. Their numbers often increase during infections, such as human immunodeficiency virus, and at sites of chronic inflammation. However, the turnover dynamics of human γδ T cells are poorly understood. Here we observed that despite more rapid proliferation in vitro by human Lyme arthritis synovial γδ T cells of the Vδ1 subset, they have reduced surviving cell numbers compared with αβ T cells because of increased cell death by the γδ T cells. Because caspases are involved in cell proliferation and death, and because signaling is more efficient through T cell receptor (TCR)-γδ than through TCR-αβ, we examined the levels of active caspases during cell cycling and following TCR restimulation. We observed higher overall caspase activity in Borrelia-reactive γδ T cells than in comparable αβ T cells. This was paralleled by greater spontaneous cell death and TCR restimulation-induced cell death of the γδ T cells, which was caspase dependent. Our current findings thus are consistent with a model in which human γδ T cells evolved to function quickly and transiently in an innate fashion.

Reduced immune response to Borrelia burgdorferi in the absence of γδ T cells

Little is known regarding the function of γδ T cells, although they accumulate at sites of inflammation in infections and autoimmune disorders. We previously observed that γδ T cells in vitro are activated by Borrelia burgdorferi in a TLR2-dependent manner. We now observe that the activated γδ T cells can in turn stimulate dendritic cells in vitro to produce cytokines and chemokines that are important for the adaptive immune response. This suggested that in vivo γδ T cells may assist in activating the adaptive immune response. We examined this possibility in vivo and observed that γδ T cells are activated and expand in number during Borrelia infection, and this was reduced in the absence of TLR2. Furthermore, in the absence of γδ T cells, there was a significantly blunted response of adaptive immunity, as reflected in reduced expansion of T and B cells and reduced serum levels of anti-Borrelia antibodies, cytokines, and chemokines. This paralleled a greater Borrelia burden in γδ-deficient mice as well as more cardiac inflammation. These findings are consistent with a model of γδ T cells functioning to promote the adaptive immune response during infection.

Current progress in γδ T-cell biology

T lymphocytes bearing γ- and δ-chain T-cell receptor heterodimers are named γδ T cells. Interestingly, γδ and αβ T cells share the same progenitors, and they undergo a fate decision in the thymus. Functional differentiation of γδ T cells occurs both inside and outside the thymus. Antigen recognition of γδ T-cell receptors is very unique, and the responses frequently exhibit innate characteristics. Nevertheless, peripheral γδ T cells exert a number of effector and regulatory functions. γδ T cells rapidly produce cytokines like interferon (IFN)-γ and IL-17 and promote inflammation, partly due to the inherent epigenetic and transcriptional programs, which facilitates a quick and extensive response. Moreover, γδ T cells lyse target cells directly, and this is necessary for pathogen or tumor clearance. γδ T cells can even serve as regulatory cells, and may contribute to immune suppression. Orchestration of γδ T-cell and other immune cell interactions may be critical for host defense and immune regulation. Recently, γδ T cells have been used for immunotherapy for infectious diseases and malignancy. In this review, we summarize the abstracts presented at the recent γδ T cell Conference held from 19 to 21 May 2010, in Kiel, Germany (please see the website for details: http://www.gammadelta-conference.uni-kiel.de/index.html).

γδ T cells enhance autoimmunity by restraining regulatory T cell responses via an interleukin-23-dependent mechanism

Mice that lack interleukin-23 (IL-23) are resistant to T cell-mediated autoimmunity. Although IL-23 is a maturation factor for T helper 17 (Th17) cells, a subset of γδ T cells expresses the IL-23 receptor (IL-23R) constitutively. Using IL-23R reporter mice, we showed that γδ T cells were the first cells to respond to IL-23 during experimental autoimmune encephalomyelitis (EAE). Although γδ T cells produced Th17 cell-associated cytokines in response to IL-23, their major function was to prevent the development of regulatory T (Treg) cell responses. IL-23-activated γδ T cells rendered αβ effector T cells refractory to the suppressive activity of Treg cells and also prevented the conversion of conventional T cells into Foxp3(+) Treg cells in vivo. Thus, IL-23, which by itself has no direct effect on Treg cells, is able to disarm Treg cell responses and promote antigen-specific effector T cell responses via activating γδ T cells.

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

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

Profiling of the early transcriptional response of murine gammadelta T cells following TCR stimulation

Gammadelta T cells represent one of the three lineages of lymphocytes, along with alphabeta T cells and B cells, which express antigen receptors. Since their discovery over two decades ago, considerable effort has been made to understand their antigen specificity and their contribution to the immune response. From these studies, we have learned that gammadelta T cells recognize a different set of antigens than alphabeta T cells, acquire effector functions faster than alphabeta T cells, regulate the response of other immune cells during infection, and play distinct roles in immunity. The molecular basis for how gammadelta T cells manifest their unique functions, however, remains unknown. To address this, we profiled the genes upregulated soon after TCR stimulation in order to identify which gene networks associated with T cell effector function are induced in gammadelta T cells. Interestingly, most of the genes in this transcriptional profile were not unique to activated gammadelta T cells, as they were also expressed in activated alphabeta T cells. However, many of the genes within this profile were upregulated with faster kinetics and/or greater magnitude in activated gammadelta T cells than in activated alphabeta T cells. In addition, we found that the genes in the transcriptional profile of activated wild-type gammadelta T cells can be used as a standard to screen activated gammadelta T cells from mice with potential signaling defects for alterations in gammadelta TCR signal transduction. Thus, by defining the early transcriptional response of activated wild-type gammadelta T cells and by comparing their transcriptional profile to that of activated wild-type alphabeta T cells as well as to that of activated gammadelta T cells from signaling defective mice, we are able to gain important insights into the molecular basis for gammadelta T cell function.

Role of γδ T Cells in Lung Inflammation

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

Activation of gamma delta T cells by Borrelia burgdorferi is indirect via a TLR- and caspase-dependent pathway

Activation of the innate immune system typically precedes engagement of adaptive immunity. Cells at the interface between these two arms of the immune response are thus critical to provide full engagement of host defense. Among the innate T cells at this interface are gammadelta T cells. gammadelta T cells contribute to the defense from a variety of infectious organisms, yet little is understood regarding how they are activated. We have previously observed that human gammadelta T cells of the Vdelta1 subset accumulate in inflamed joints in Lyme arthritis and proliferate in response to stimulation with the causative spirochete, Borrelia burgdorferi. We now observe that murine gammadelta T cells are also activated by B. burgdorferi and that in both cases the activation is indirect via TLR stimulation on dendritic cells or monocytes. Furthermore, B. burgdorferi stimulation of monocytes via TLR, and secondary activation of gammadelta T cells, are both caspase-dependent.

Gammadelta T cells do not require fully functional cytotoxic pathways or the ability to recognize recipient alloantigens to prevent graft rejection

Gammadelta T cells are a unique and minor T-cell subset that differs from conventional alphabeta T cells by virtue of their tissue localization and antigen processing requirements. We have previously shown that ex vivo-activated gammadelta T cells are able to prevent graft rejection without causing clinically significant graft-versus-host disease (GVHD). In the present study, we examined how gammadelta T cells facilitate alloengraftment and to what extent mechanisms used by conventional alphabeta T cells are also used by gammadelta T cells. We observed that, unlike alphabeta T cells, for which CD8(+) T cells are primarily responsible for facilitating engraftment, purified CD8(+)gammadelta(+) T cells administered at the same fractional dose as for the unseparated activated gammadelta T-cell population were insufficient to prevent graft rejection. Furthermore, the ability to prevent graft rejection was not affected by the absence of fully functional fas ligand or perforin cytotoxic pathways, nor was it contingent on the ability of gammadelta T cells to recognize recipient major histocompatibility process alloantigens. Repetitive infusions of a suboptimal dose of gammadelta T cells however were able to rescue mice from graft rejection, suggesting that the persistence of these cells in vivo was critical in facilitating alloengraftment. These studies demonstrate that gammadelta T cells do not use mechanisms used by conventional nontolerant alphabeta T cells to prevent graft rejection. The ability of these cells to promote engraftment without causing GVHD further distinguishes these cells from alphabeta T cells and may be an attribute that can be exploited in the clinical transplantation setting.

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.

Co-inoculation of Borrelia afzelii with tick salivary gland extract influences distribution of immunocompetent cells in the skin and lymph nodes of mice

The impact of Ixodes ricinus salivary gland extract (SGE) on inflammatory changes in the skin and draining lymph nodes of mice, elicited by the infection with the important human pathogen, B. afzelii, was determined using flow cytometry. SGE injected together with spirochetes reduced the numbers of leukocytes and gammadelta-T lymphocytes in infected epidermis at early time-points post infection. In draining lymph nodes, the anti-inflammatory effect of SGE was manifested by the decrease of total cell count compared with that in mice treated with inactivated SGE. Changes in subpopulations of immunocompetent cells apparently reflected the effect of SGE on the proliferation of spirochetes in the host. The significance of tick saliva anti-inflammatory effect for saliva activated transmission of B. afzelii is shown.

Lyme arthritis synovial gammadelta T cells instruct dendritic cells via fas ligand

gammadelta T cells participate in the innate immune response to a variety of infectious microorganisms. They also link to the adaptive immune response through their induction of maturation of dendritic cells (DC) during the early phase of an immune response when the frequency of Ag-specific T cells is very low. We observe that in the presence of Borrelia burgdorferi, synovial Vdelta1 T cells from Lyme arthritis synovial fluid potently induce maturation of DC, including production of IL-12, and increased surface expression of CD40 and CD86. The activated DC are then able to stimulate the Vdelta1 T cells to up-regulate CD25. Both of these processes are initiated primarily by Fas stimulation rather than CD40 activation of DC via high expression of Fas ligand by the Vdelta1 T cells. DC are resistant to Fas-induced death due to expression of high levels of the Fas inhibitor c-FLIP. This effect serves to divert Fas-mediated signals from the caspase cascade to the ERK MAPK and NF-kappaB pathways. The findings affirm the importance of the interaction of certain T cell populations with DC during the early phases of the innate immune response. They also underscore the view that as levels of c-FLIP increase, Fas signaling can be diverted from induction of apoptosis to pathways leading to cell effector function.

Distinct mechanisms of CD4+ and CD8+ T-cell activation and bystander apoptosis induced by human immunodeficiency virus type 1 virions

Apoptosis of uninfected bystander T cells contributes to T-cell depletion during human immunodeficiency virus type 1 (HIV-1) infection. HIV-1 envelope/receptor interactions and immune activation have been implicated as contributors to bystander apoptosis. To better understand the relationship between T-cell activation and bystander apoptosis during HIV-1 pathogenesis, we investigated the effects of the highly cytopathic CXCR4-tropic HIV-1 variant ELI6 on primary CD4(+) and CD8(+) T cells. Infection of primary T-cell cultures with ELI6 induced CD4(+) T-cell depletion by direct cell lysis and bystander apoptosis. Exposure of primary CD4(+) and CD8(+) T cells to nonreplicating ELI6 virions induced bystander apoptosis through a Fas-independent mechanism. Bystander apoptosis of CD4(+) T cells required direct contact with virions and Env/CXCR4 binding. In contrast, the apoptosis of CD8(+) T cells was triggered by a soluble factor(s) secreted by CD4(+) T cells. HIV-1 virions activated CD4(+) and CD8(+) T cells to express CD25 and HLA-DR and preferentially induced apoptosis in CD25(+)HLA-DR(+) T cells in a CXCR4-dependent manner. Maximal levels of binding, activation, and apoptosis were induced by virions that incorporated MHC class II and B7-2 into the viral membrane. These results suggest that nonreplicating HIV-1 virions contribute to chronic immune activation and T-cell depletion during HIV-1 pathogenesis by activating CD4(+) and CD8(+) T cells, which then proceed to die via apoptosis. This mechanism may represent a viral immune evasion strategy to increase viral replication by activating target cells while killing immune effector cells that are not productively infected.

Gamma delta T cells regulate the extent and duration of inflammation in the central nervous system by a Fas ligand-dependent mechanism

Gamma delta T cells have been shown to regulate immune responses associated with inflammation, but the mechanism of this regulation is largely unknown. Using the experimental autoimmune encephalomyelitis (EAE) model of the human CNS autoimmune disease multiple sclerosis, we demonstrate that gamma delta T cells are important regulators of CNS inflammation. This was shown using gamma delta T cell-deficient mice that were unable to recover from EAE. The chronic disease was accompanied by a prolonged presence of both macrophages and lymphocytes in the CNS. This extended inflammatory response was due to alterations in both cell proliferation and death. In mice lacking gamma delta T cells, proliferation of encephalitogenic T cells was 3-fold higher, and caspase activity, indicating apoptosis, was 2-fold lower compared with those in control mice recovering from EAE. gamma delta T cell-deficient mice reconstituted with wild-type gamma delta T cells recovered from EAE and resolved inflammation in the CNS, whereas mice reconstituted with Fas ligand-dysfunctional gamma delta T cells did not. Thus, gamma delta T cells regulate both inflammation in the CNS and disease recovery via Fas/Fas ligand-induced apoptosis of encephalitogenic T cells, and a quick resolution of inflammation in the CNS is essential to prevent permanent damage to the CNS resulting in chronic disease.

Fas-Fas ligand interactions are essential for the binding to and killing of activated macrophages by gamma delta T cells

Gammadelta T cells have a direct role in resolving the host immune response to infection by eliminating populations of activated macrophages. Macrophage reactivity resides within the Vgamma1/Vdelta6.3 subset of gammadelta T cells, which have the ability to kill activated macrophages following infection with Listeria monocytogenes (Lm). However, it is not known how gammadelta T cell macrophage cytocidal activity is regulated, or what effector mechanisms gammadelta T cells use to kill activated macrophages. Using a macrophage-T cell coculture system in which peritoneal macrophages from naive or Lm-infected TCRdelta-/- mice were incubated with splenocytes from wild-type and Fas ligand (FasL)-deficient mice (gld), the ability of Vgamma1 T cells to bind macrophages was shown to be dependent upon Fas-FasL interactions. Combinations of anti-TCR and FasL Abs completely abolished binding to and killing of activated macrophages by Vgamma1 T cells. In addition, confocal microscopy showed that Fas and the TCR colocalized on Vgamma1 T cells at points of contact with macrophages. Collectively, these studies identify an accessory or coreceptor-like function for Fas-FasL that is essential for the interaction of Vgamma1 T cells with activated macrophages and their elimination during the resolution stage of pathogen-induced immune responses.

Mechanisms of Vδ1 γδ T Cell Activation by Microbial Components

There are two major subsets of gammadelta T cell in humans. Vgamma2Vdelta2 T cells predominate in the circulation and significantly expand in vivo during a variety of infectious diseases. Ags identified for the Vdelta2 T cells are nonpeptide phosphate, amine, and aminobisphosphonate compounds. In contrast, Vdelta1-encoded TCRs account for the vast majority of gammadelta T cells in tissues such as intestine and spleen. Some of these T cells recognize CD1c and MHC class I-related chain (MICA/B) molecules [correction]. These T cells are cytotoxic and use both perforin- and Fas-mediated cytotoxicity. A fundamental question is how these gammadelta T cells are activated during microbial exposure to carry out effector functions. In this study, we provide evidence for a mechanism by which Vdelta1 gammadelta T cells are activated by inflammatory cytokines in the context of the Vdelta1 TCR. Dendritic cells are necessary as accessory cells for microbial Ag-mediated Vdelta1 gammadelta T cell activation. Cytokine (IL-12), adhesion (LFA3/CD2, LFA1/ICAM1) and costimulatory (MHC class I-related chain (MICA/B) molecules/NK-activating receptor G2D) molecules play a significant role along with Vdelta1 TCR in this activation.

The multiple roles of Fas ligand in the pathogenesis of infectious diseases

Fas ligand (FasL) is a type II transmembrane protein that plays a critical role in immune homeostasis by binding to its receptor Fas (CD95) and inducing apoptosis. Fas/FasL dysregulation contributes to infectious disease pathogenesis. Microorganisms may inhibit Fas signal transduction to prolong intracellular survival and prevent killing by immune effector cells. FasL may be upregulated in directly infected cells to enhance killing of responding immune cells and facilitate immune evasion. The host response to infection may aim to induce apoptosis in directly infected cells, but immune cells that target directly infected cells can induce Fas-mediated apoptosis of uninfected bystander cells. FasL also contributes to the generation and regulation of the inflammatory response in infection. The multiple roles of FasL in infectious disease pathogenesis are discussed in the context of viral, bacterial and parasitic infections.

Leptospira interrogans activation of human peripheral blood mononuclear cells: preferential expansion of TCR gamma delta+ T cells vs TCR alpha beta+ T cells

Innate and adaptive immune responses induced by leptospirosis have not been well characterized. In this study we show that in vitro exposure of naive human PBMC to Leptospira interrogans results in cell proliferation and the production of IFN-gamma, IL-12, and TNF-alpha. Cell proliferation was highest when using high numbers of Leptospira. Optimal cell proliferation occurred at 6-8 days, and the majority of cells contained in these cultures were gamma/delta T cells. These cultures showed a 10- to 50-fold expansion of gamma/delta T cells compared with the initial cellular input. Additionally, these cultures contained elevated numbers of NK cells. In contrast, exposure of PBMC to low numbers of Leptospira failed to induce gammadelta T cell or NK cell expansion, but induced significant alphabeta T cell expansion. Vgamma9/Vdelta2 were expressed on all gamma/delta T cells expanded by exposure of PBMC to Leptorspira: Leptospira stimulation of purified TCRgammadelta(+) T cells, obtained from 8-day cultures of Leptospira-stimulated PBMC, induced high levels of IFN-gamma production, but no cell proliferation, suggesting that such stimulation of gammadelta T cells did not depend on specialized accessory cells or Ag processing. Finally, in patients with acute leptospirosis, there was a significant (4- to 5-fold) increase in the number of peripheral blood TCRgammadelta(+) T cells. These results indicate that Leptospira can activate gammadelta T cells and alphabeta T cells and will guide further investigations into the roles of these T cell populations in host defense and/or the pathology of leptospirosis.

Differential requirements for proliferation of CD4+ and γδ+ T cells to spirochetal antigens

Alphabeta+ and gammadelta+ T cells have different mechanisms of epitope recognition and are stimulated by antigens of different chemical nature. An immunization model with antigens from the spirochete Brachyspira hyodysenteriae was used to examine the requirements for proliferation of circulating porcine CD4+ and gammadelta+ T cells in mixed lymphocyte cultures. CD4+ T cells only responded to stimulation with B. hyodysenteriae antigens, whereas gammadelta+ T cells proliferated when cultures were stimulated with either spirochetal antigens or interleukin-2 (IL-2). T cells that had proliferated expressed high levels of IL-2-receptor-alpha (IL-2Ralpha). Furthermore, neutralization of IL-2 at the beginning of the culture period was more efficient in blocking gammadelta+ than CD4+ T cell proliferation. Immunization induced interferon-gamma (IFN-gamma) production by CD4+ T cells, whereas only a small fraction of the antigen-stimulated gammadelta+ T cells produced this cytokine. Our results indicate that, under the same environmental conditions, CD4+ T cell functions are more tightly regulated when compared to gammadelta+ T cells. We conclude that these differences are due, in part, to the enhanced gammadelta+ T cell responsiveness to IL-2.

Study of Herpesvirus saimiri immortalization of gammadelta T cells derived from peripheral blood and CSF of multiple sclerosis patients

Human gammadelta T cells are an integral part of the innate immune system and have been difficult to study owing primarily to their relatively low abundance and their fastidious culture properties associated with short in vitro lifespan. Their increased presence within multiple sclerosis (MS) white matter plaques compared to peripheral blood (PB) suggests a specific interaction with central nervous system (CNS) tissues. This fact, together with their innate ability to lyse human oligodendrocytes in culture implicate them possibly in the pathogenesis of MS. To further investigate their potential role in MS, we studied whether gammadelta T cells could be effectively immortalized using Herpesvirus saimiri (HVS), so that they could be studied in longer-term cultures. Effective culture conditions were established resulting in efficient HVS growth transformation of multiple PB and CSF gammadelta T cell lines and clones that could exist in IL-2-dependent culture for periods in excess of 2 years. Phenotypic and functional comparison studies with parental nontransformed gammadelta T cells were performed to characterize the changes that possibly induced by viral transformation. Using panels of transformed gammadelta T cell clones representing discrete gammadelta TcR subtypes, there was no apparent correlation between intracytoplasmic cytokine expression or tumor cell cytotoxicity with a specific TcR. All transformed gammadelta T cells analyzed, regardless of their compartment of origin, strongly expressed intracytoplasmic IFN-gamma and TNF-alpha, but little IL-2 or anti-inflammatory IL-4 or IL-10. These results indicate that HVS transformation of gammadelta T cells can be used to generate lines and clones from both the CSF and PB compartments for further study and elucidation of their potential role in MS pathogenesis.

High expression of Fas ligand by synovial fluid-derived gamma delta T cells in Lyme arthritis

Gamma delta T cells accumulate at epithelial barriers and at sites of inflammation in various infectious and autoimmune diseases, yet little is understood about the function of tissue-infiltrating gamma delta T cells. We observe that gamma delta T cells of the V delta 1 subset accumulate in synovial fluid of human Lyme arthritis and are intensely cytolytic toward a wide array of target cells. Particularly striking is that the cytolytic activity is highly prolonged, lasting for at least 3 wk after stimulation of the gamma delta T cells with Borrelia burgdorferi. Cytolysis is largely Fas dependent and results from very high and prolonged expression of surface Fas ligand, which is transcriptionally regulated. This also manifests in a substantial level of self-induced apoptosis of the gamma delta T cells. In this capacity, certain gamma delta T cell subsets may serve as cytolytic sentinels at sites of inflammation, and perhaps at epithelial barriers.

Immunoregulation in the tissues by gammadelta T cells

For a T-cell subset to be classified as immunoregulatory, it might reasonably be predicted that in its absence, animals would experience pathological immune dysregulation. Moreover, reconstitution of the subset should restore normal immune regulation. So far, these criteria have been satisfied by only a few of the candidate regulatory T-cell subsets, but among them is the intraepithelial gammadelta T-cell receptor (TCR)+ subset of mouse skin. In this article, we look at immunoregulatory gammadelta T cells, and the growing evidence for tissue-associated immunoregulation mediated by both gammadelta T cells and alphabeta T cells.

Vgamma4(+) T cells promote autoimmune CD8(+) cytolytic T-lymphocyte activation in coxsackievirus B3-induced myocarditis in mice: role for CD4(+) Th1 cells

T cells expressing the Vgamma4 T-cell receptor (TCR) promote myocarditis in coxsackievirus B3 (CVB3)-infected BALB/c mice. CD1, a major histocompatibility complex (MHC) class I-like molecule, is required for activation of Vgamma4(+) cells. Once activated, Vgamma4(+) cells initiate myocarditis through gamma interferon (IFN-gamma)-mediated induction of CD4(+) T helper type 1 (Th1) cells in the infected animal. These CD4(+) Th1 cells are required for activation of an autoimmune CD8(+) alphabeta TCR(+) effector, which is the predominant pathogenic agent in this model of CVB3-induced myocarditis. Activated Vgamma4(+) cells can adoptively transfer myocarditis into BALB/c mice infected with a nonmyocarditic variant of CVB3 (H310A1) but cannot transfer myocarditis into either uninfected or CD1(-/-) recipients, demonstrating the need for both infection and CD1 expression for Vgamma4(+) cell function. In contrast, CD8(+) alphabeta TCR(+) cells transfer myocarditis into either infected CD1(-/-) or uninfected recipients, showing that once activated, the CD8(+) alphabeta TCR(+) effectors function independently of both virus and CD1. Vgamma4(+) cells given to mice lacking CD4(+) T cells minimally activate the CD8(+) alphabeta TCR(+) cells. These studies show that Vgamma4(+) cells determine CVB3 pathogenicity by their ability to influence both the CD4(+) and CD8(+) adaptive immune response. Vgamma4(+) cells enhance CD4(+) Th1 (IFN-gamma(+)) cell activation through IFN-gamma- and CD1-dependent mechanisms. CD4(+) Th1 cells promote activation of the autoimmune CD8(+) alphabeta TCR(+) effectors.

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.

GammadeltaT cells regulate the development of hapten-specific CD8+ effector T cells in contact hypersensitivity responses

It has been reported that gammadeltaT cells are required for transfer of contact hypersensitivity responses by hapten-primed T cells. The mechanism by which they do so, however, remains to be elucidated. To specifically investigate the role of gammadeltaT cells in the development of contact hypersensitivity, this study employed Tdelta gene knockout mice that are deficient in gammadeltaT cells but are normal in the development of alphabetaT cells. The result indicates that contact hypersensitivity responses were significantly greater in gammadeltaT cell deficient mice than in wild-type mice. Similar results were obtained when wild-type mice were depleted of gammadeltaT cells with antibody treatment before hapten sensitization. Depletion of CD4+ T cells did not affect the increased contact hypersensitivity response in gammadeltaT cell deficient mice, suggesting that the effect of gammadeltaT cells is on CD8+ T cells and does not require CD4+ T cells. Further experiments demonstrated that primed CD8+ T cells from the deficient mice exhibited significantly higher CTL activity. The cytokine profile of CD4+ T cells was not significantly altered. Transfer of primed lymph node cells from hapten-primed gammadeltaT cell deficient mice elicited a similar level of contact hypersensitivity in naive wild-type and the deficient recipient mice, indicating that gammadeltaT cells have little effect on the elicitation of primed T cells and contact hypersensitivity responses. We conclude that gammadeltaT cells downregulate contact hypersensitivity responses to hapten sensitization by limiting the development of hapten-specific CD8+ effector T cells during sensitization and that this effect is independent of CD4+ T cells.

Gammadelta T cells promote a Th1 response during coxsackievirus B3 infection in vivo: role of Fas and Fas ligand

Fas/Fas ligand (FasL) interactions regulate disease outcome in coxsackievirus B3 (CVB3)-induced myocarditis. MRL(+/+) mice infected with CVB3 develop severe myocarditis, a dominant CD4(+) Th1 (gamma interferon [IFN-gamma(+)]) response to the virus, and a predominance of gammadelta T cells in the myocardial infiltrates. MRL lpr/lpr and MRL gld/gld mice, which lack normal expression of Fas and express a mutated FasL, respectively, have minimal myocarditis and show a dominant CD4(+) Th2 (interleukin-4 [IL-4(+)]) phenotype to CVB3. Spleen cells from virus-infected wild-type, lpr, and gld animals proliferate equally to virus in vitro. Adoptive transfer of gammadelta T cells from hearts of CVB3-infected MRL(+/+) mice (FasL(+)) into infected MRL gld/gld recipients (FasL(-)/Fas(+)) restores both disease susceptibility and Th1 cell phenotype. However, transfer of these cells into MRL lpr/lpr recipients (FasL(+)/Fas(-)) did not promote myocarditis and the viral response remained Th2 biased. This paralleled the expression of very high surface levels of FasL by myocardial gammadelta T cells, as well as their propensity to selectively lyse Th2 virus-specific CD4(+) T cells. These results demonstrate that Fas/FasL interactions conferred by gammadelta T cells on lymphocyte subpopulations may regulate the cytokine response to CVB3 infection and pathogenicity.

Gammadelta T cells: functional plasticity and heterogeneity

Gammadelta T cells remain an enigma. They are capable of generating more unique antigen receptors than alphabeta T cells and B cells combined, yet their repertoire of antigen receptors is dominated by specific subsets that recognize a limited number of antigens. A variety of sometimes conflicting effector functions have been ascribed to them, yet their biological function(s) remains unclear. On the basis of studies of gammadelta T cells in infectious and autoimmune diseases, we argue that gammadelta T cells perform different functions according to their tissue distribution, antigen-receptor structure and local microenvironment; we also discuss how and at what stage of the immune response they become activated.

gammadelta T cell subsets in patients with arthritis and chronic neutropenia

BACKGROUND

An abnormal distribution of subsets of gammadelta T cells, which are a component of the inflammatory infiltrate in arthritic synovium, has been demonstrated in the peripheral blood (PB) of patients with arthritis and neutropenia.

OBJECTIVE

To evaluate whether the clinical manifestations of patients with arthritis and neutropenia are related to the specific gammadelta T cell subset predominant in the PB.

METHODS

Flow cytometry of PB lymphocytes in six consecutive patients with chronic neutropenia and arthritis was performed. Variable (V) gamma and delta gene families were analysed by polymerase chain reaction. cDNA was subjected to direct automated sequencing of T cell receptor (TCR) genes.

RESULTS

Three patients had non-deforming and non-erosive rheumatoid factor (RF)(+) polyarticular rheumatoid arthritis, RF(+) oligoarticular arthritis, or RF(-) non-deforming oligoarticular psoriatic arthritis with persistent expansions of Vgamma1(+)/Vdelta2(+), Vgamma2(+)/Vdelta2(+), or Vgamma1(+)/Vdelta (undetermined (2- 1-)) T cells, respectively. The other three patients, without persistent expansion of gammadelta T cells, had either non-deforming and non-erosive oligo- or polyarthritis with a balanced distribution of several Vdelta and Vgamma genes, or severe erosive RF(+) arthritis with deficiency of all but Vgamma1(+)/Vdelta1(+) T cells.

CONCLUSIONS

gammadelta T cell lymphoproliferations in chronic neutropenia and arthritis use different Vgamma and Vdelta gene families, often forming T cell receptor (TCR) structures that are infrequent in normal adult PB. Arthritis with Vgamma1(+)/Vdelta2(+), Vgamma2(+)/Vdelta2(+), or Vgamma1(+)/Vdelta2(-)/Vdelta1(-) gammadelta T cells in the PB is non-deforming and non-erosive, suggesting a protective effect of these cells, as opposed to a more pathogenic contribution of Vgamma1(+)/Vdelta1(+) cells.

Long-term influence of lipid nutrition on the induction of CD8(+) responses to viral or bacterial antigens

Porcine CD8(+) lymphocytes are critical for the development of cellular immune responses to bacterial (i.e. CD8alphaalpha(+)) and viral (i.e. CD8alphabeta(+) lymphocytes) pathogens. Vaccination and challenge modulate the kinetics of appearance of CD8(+) cells in peripheral blood. In addition to antigen-mediated modulation, nutritional modulation can also influence cell-mediated immunity. We had previously observed that diets supplemented with a mixture of conjugated linoleic acid (CLA) isomers expanded porcine CD8(+) peripheral blood mononuclear cells (PBMC). The present study aimed to investigate the influence of prior consumption of a nutraceutical, (i.e. dietary CLA) on phenotypes and effector functions of porcine PBMC following immunization with a bacterin or a modified-live viral vaccine. It was demonstrated that the effects of dietary CLA on immune cell phenotype (i.e. numbers of CD8alphabeta(+) cells) persisted after the compound was withdrawn from the diet (i.e. 67 days), whereas effector functions (i.e. antigen-stimulated proliferation and cytotoxicity) disappeared earlier (i.e. 25 days). Specifically, numbers of CD8alphabeta(+) PBMC in pigs that had been fed diets supplemented with CLA were greater than in pigs fed control (i.e. isoenergetic and unsupplemented) diets, regardless of the vaccination treatment. Furthermore, prior dietary CLA supplementation interacted with viral immunization (i.e. modified-live pseudorabies virus (PRV) vaccine) by enhancing both pseudorabies-specific proliferative responses of CD8alphabeta(+) PBMC and granzyme activities of PBMC.

gammadelta T cells express activation markers in the central nervous system of mice with chronic-relapsing experimental autoimmune encephalomyelitis

In this study, we assessed the expression of activation markers on gammadelta T cells in central nervous system (CNS) lesions of SJL mice adoptively sensitized to develop experimental autoimmune encephalomyelitis (EAE) using myelin basic protein-reactive T cells. Although disease expression is known to be dependent upon T cells that express the alphabeta T cell receptor (TCR), a role for gammadelta T cells has been implicated in some studies but not in others. Using three-color flow cytometric analysis of both total and gammadelta T cells in spleen and CNS, the data showed that expression of CD69 (early activation marker), CD62L (lymphocyte homing receptor), CD25 (IL-2Ralpha), CD122 (IL-2Rbeta) and CD95/CD95L (Fas/FasL), fluctuated on gammadelta T cells in EAE lesions in a disease-related fashion. Furthermore, the pattern of expression for these markers on gammadelta T cells was distinct from that found on the total lymphocyte population. Cytokine analysis of gammadelta T cells in the CNS demonstrated a bias towards a Th1-like cytokine profile. From these data, we conclude that gammadelta T cells in EAE lesions display an activated phenotype and form a dynamic component of the total lymphocyte population in the CNS, supporting a contributory role for these cells.

Protective killed Leptospira borgpetersenii vaccine induces potent Th1 immunity comprising responses by CD4 and gammadelta T lymphocytes

Leptospira borgpetersenii serovar hardjo is the most common cause of bovine leptospirosis and also causes zoonotic infections of humans. A protective killed vaccine against serovar hardjo was shown to induce strong antigen-specific proliferative responses by peripheral blood mononuclear cells (PBMC) from vaccinated cattle by 2 months after the first dose of vaccine. This response was absent from nonvaccinated control cattle. The mean response peaked by 2 months after completion of the two-dose vaccination regimen, and substantial proliferation was measured in in vitro cultures throughout the 7 months of the study period. Variations in magnitude of the response occurred among the vaccinated animals, but by 7 months postvaccination there was a substantial antigen-specific response with PBMC from all vaccinated animals. Up to one-third of the PBMC from vaccinated animals produced gamma interferon (IFN-gamma) after 7 days in culture with antigen, as ascertained by flow cytometric analysis, and significant levels of IFN-gamma were measured in culture supernatants by enzyme-linked immunosorbent assay. Two-color immunofluorescence revealed that one-third of the IFN-gamma-producing cells were gammadelta T cells, with the remaining cells being CD4(+) T cells. The significance of this study is the very potent Th1-type immune response induced and sustained following vaccination with a killed bacterial vaccine adjuvanted with aluminum hydroxide and the involvement of gammadelta T cells in the response. Moreover, induction of this Th1-type cellular immune response is associated with the protection afforded by the bovine leptospiral vaccine against L. borgpetersenii serovar hardjo.

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.