T cell receptor-gamma/delta cells protect mice from herpes simplex virus type 1-induced lethal encephalitis

Expansion of effector memory Vδ2neg γδ T cells associates with cytomegalovirus reactivation in allogeneic stem cell transplant recipients

Background

Cytomegalovirus (CMV) reactivation is a significant concern following allogeneic stem cell transplantation. While previous research has highlighted the anti-CMV reactivation effect of γδ T cells in immunocompromised transplant patients, their characterization in recipients at high risk of CMV reactivation remains limited.

Methods

This study focused on D+/R+ recipients (where both donor and recipient are CMV seropositive) at high risk of CMV reactivation. We analyzed 28 patients who experienced CMV recurrence within 100 days post-allogeneic hematopoietic stem cell transplantation, along with 36 matched recipients who did not experience CMV recurrence. Clinical data from both groups were compared, and risk factors for CMV reactivation were identified. Additionally, CMV viral load was measured, and flow cytometric analysis was conducted to assess changes in peripheral blood γδ T cell proportions, subpopulation distribution, and differentiation status. We also analyzed the CDR3 repertoire of the TCR δ chain in different γδ T cell subsets. Functional analysis was performed by measuring the lysis of CMV-infected cells upon stimulation.

Results

CMV reactivation post-transplantation was associated with acute graft-versus-host disease (aGvHD) and reactivation of non-CMV herpesviruses. Notably, CMV reactivation led to sustained expansion of γδ T cells, primarily within the Vδ2neg γδ T cell subpopulation, with a trend toward differentiation from Naive to effector memory cells. Analysis of the δ chain CDR3 repertoire revealed a delay in the reconstitution of clonal diversity in Vδ2neg γδ T cells following CMV reactivation, while Vδ2pos T cells remained unaffected. Upon stimulation with CMV-infected MRC5 cells, the Vδ2neg γδ T cell subpopulation emerged as the primary effector cell group producing IFN-γ and capable of lysing CMV-infected cells. Moreover, our findings suggest that NKG2D is not necessary involved in Vδ2neg γδ T cell-mediated anti-CMV cytotoxicity.

Conclusion

This study provides novel insights into the role of γδ T cells in the immune response to CMV reactivation in transplantation recipients at high risk of CMV infection. Specifically, the Vδ2neg γδ T cell subpopulation appears to be closely associated with CMV reactivation, underscoring their potential role in controlling infection and reflecting CMV reactivation in HSCT patients.

Effect of Pre-Treatment with a Recombinant Chicken Interleukin-17A on Vaccine Induced Immunity against a Very Virulent Marek's Disease Virus

The host response to pathogenic microbes can lead to expression of interleukin (IL)-17, which has antimicrobial and anti-viral activity. However, relatively little is known about the basic biological role of chicken IL-17A against avian viruses, particularly against Marek's disease virus (MDV). We demonstrate that, following MDV infection, upregulation of IL-17A mRNA and an increase in the frequency of IL-17A+ T cells in the spleen occur compared to control chickens. To elaborate on the role of chIL-17A in MD, the full-length chIL-17A coding sequence was cloned into a pCDNA3.1-V5/HIS TOPO plasmid. The effect of treatment with pcDNA:chIL-17A plasmid in combination with a vaccine (HVT) and very virulent(vv)MDV challenge or vvMDV infection was assessed. In combination with HVT vaccination, chickens that were inoculated with the pcDNA:chIL-17A plasmid had reduced tumor incidence compared to chickens that received the empty vector control or that were vaccinated only (66.6% in the HVT + empty vector group and 73.33% in HVT group versus 53.3% in the HVT + pcDNA:chIL-17A). Further analysis demonstrated that the chickens that received the HVT vaccine and/or plasmid expressing IL-17A had lower MDV-Meq transcripts in the spleen. In conclusion, chIL-17A can influence the immunity conferred by HVT vaccination against MDV infection in chickens.

A Comparison of Pseudorabies Virus Latency to Other A-Herpesvirinae Subfamily Members

Pseudorabies virus (PRV), the causative agent of Aujeszky’s disease, is one of the most important infectious pathogens threatening the global pig industry. Like other members of alphaherpesviruses, PRV establishes a lifelong latent infection and occasionally reactivates from latency after stress stimulus in infected pigs. Latent infected pigs can then serve as the source of recurrent infection, which is one of the difficulties for PRV eradication. Virus latency refers to the retention of viral complete genomes without production of infectious progeny virus; however, following stress stimulus, the virus can be reactivated into lytic infection, which is known as the latency-reactivation cycle. Recently, several research have indicated that alphaherpesvirus latency and reactivation is regulated by a complex interplay between virus, neurons, and the immune system. However, with those limited reports, the relevant advances in PRV latency are lagging behind. Therefore, in this review we focus on the regulatory mechanisms in PRV latency via summarizing the progress of PRV itself and that of other alphaherpesviruses, which will improve our understanding in the underlying mechanism of PRV latency and help design novel therapeutic strategies to control PRV latency.

Intramuscular Vaccination With the HSV-1(VC2) Live-Attenuated Vaccine Strain Confers Protection Against Viral Ocular Immunopathogenesis Associated With γδT Cell Intracorneal Infiltration

Herpes simplex virus type-1 (HSV-1) ocular infection is one of the leading causes of infectious blindness in developed countries. The resultant herpetic keratitis (HK) is caused by an exacerbated reaction of the adaptive immune response that persists beyond virus clearance causing substantial damage to the cornea. Intramuscular immunization of mice with the HSV-1(VC2) live-attenuated vaccine strain has been shown to protect mice against lethal ocular challenge. Herein, we show that following ocular challenge, VC2 vaccinated animals control ocular immunopathogenesis in the absence of neutralizing antibodies on ocular surfaces. Ocular protection is associated with enhanced intracorneal infiltration of γδ T cells compared to mock-vaccinated animals. The observed γδ T cellular infiltration was inversely proportional to the infiltration of neutrophils, the latter associated with exacerbated tissue damage. Inhibition of T cell migration into ocular tissues by the S1P receptors agonist FTY720 produced significant ocular disease in vaccinated mice and marked increase in neutrophil infiltration. These results indicate that ocular challenge of mice immunized with the VC2 vaccine induce a unique ocular mucosal response that leads into the infiltration of γδ T cells resulting in the amelioration of infection-associated immunopathogenesis.

An Anti-Tumor Vaccine Against Marek's Disease Virus Induces Differential Activation and Memory Response of γδ T Cells and CD8 T Cells in Chickens

Marek's disease virus (MDV) is a highly oncogenic alphaherpesvirus that causes deadly T-cell lymphomas and serves as a natural virus-induced tumor model in chickens. The most efficacious vaccine, CVI988/Rispens (CVI988), against MD has been used for several decades. However, the mechanisms leading to protective immunity following vaccination are not fully understood. In this study, employing multi-parameter flow cytometry, we performed a comprehensive analysis of T cell responses in CVI988-vaccinated chickens. CVI988 vaccination induced significant expansion of γδ T cells and CD8α⁺ T cells but not CD4⁺ T cells in spleen, lung and blood at early time-points. The expansion of these cells was CVI988-specific as infection with very virulent MDV RB1B did not elicit expansion of either γδ or CD8α⁺ T cells. Phenotypic analysis showed that CVI988 vaccination elicited preferential proliferation of CD8α⁺ γδ T cells and CD8αα co-receptor expression was upregulated on γδ T cells and CD8α⁺ T cells after immunization. Additionally, cell sorting and quantitative RT-PCR showed that CVI988 vaccination activated γδ T cells and CD8α⁺ T cells which exhibited differential expression of cytotoxic and T cell-related cytokines. Lastly, secondary immunization with CVI988 induced the expansion of CD8⁺ T cells but not γδ T cells at higher magnitude, compared to primary immunization, suggesting CVI988 did induce memory CD8⁺ T cells but not γδ T cells in chickens. Our results, for the first time, reveal a potential role of γδ T cells in CVI988-induced immune protection and provide new insights into the mechanism of immune protection against oncogenic MDV.

Pathobiology and treatment of viral keratitis

Keratitis is one of the most prevalent ocular diseases manifested by partial or total loss of vision. Amongst infectious (viz., microbes including bacteria, fungi, amebae, and viruses) and non-infectious (viz., eye trauma, chemical exposure, and ultraviolet exposure, contact lens) risk factors, viral keratitis has been demonstrated as one of the leading causes of corneal opacity. While many viruses have been shown to cause keratitis (such as rhabdoviruses, coxsackieviruses, etc.), herpesviruses are the predominant etiologic agent of viral keratitis. This chapter will summarize current knowledge on the prevalence, diagnosis, and pathobiology of viral keratitis. Virus-mediated immunomodulation of host innate and adaptive immune components is critical for viral persistence, and dysfunctional immune responses may cause destruction of ocular tissues leading to keratitis. Immunosuppressed or immunocompromised individuals may display recurring disease with pronounced severity. Early diagnosis of viral keratitis is beneficial for disease management and response to treatment. Finally, we have discussed current and emerging therapies to treat viral keratitis.

Dissecting the complexity of γδ T-cell subsets in skin homeostasis, inflammation, and malignancy

γδ T cells are much less common than αβ T cells, accounting for 0.5% to 5% of all T lymphocytes in the peripheral blood and lymphoid tissues in mice and humans. However, they are the most abundant T-lymphocyte subset in some epithelial barriers such as mouse skin. γδ T cells are considered innate lymphocytes because of their non-MHC restricted antigen recognition, as well as because of their rapid response to cytokines, invading pathogens, and malignant cells. Exacerbated expansion and activation of γδ T cells in the skin is a common feature of acute and chronic skin inflammation such as psoriasis and contact or atopic dermatitis. Different γδ T-cell subsets showing differential developmental and functional features are found in mouse and human skin. This review discusses the state of the art of research and future perspectives about the role of the different subsets of γδ T-cells detected in the skin in steady-state, psoriasis, dermatitis, infection, and malignant skin diseases. Also, we highlight the differences between human and mouse γδ T cells in skin homeostasis and inflammation, as understanding the differential role of each subtype of skin γδ T cells will improve the discovery of new therapies.

The Role of Gamma-Delta T Cells in Diseases of the Central Nervous System

Gamma-delta (γδ) T cells are a subset of T cells that promote the inflammatory responses of lymphoid and myeloid lineages, and are especially vital to the initial inflammatory and immune responses. Given the capability to connect crux inflammations of adaptive and innate immunity, γδ T cells are responsive to multiple molecular cues and can acquire the capacity to induce various cytokines, such as GM-CSF, IL-4, IL-17, IL-21, IL-22, and IFN-γ. Nevertheless, the exact mechanisms responsible for γδ T cell proinflammatory functions remain poorly understood, particularly in the context of the central nervous system (CNS) diseases. CNS disease, usually leading to irreversible cognitive and physical disability, is becoming a worldwide public health problem. Here, we offer a review of the neuro-inflammatory and immune functions of γδ T cells, intending to understand their roles in CNS diseases, which may be crucial for the development of novel clinical applications.

Human Peripheral Blood Gamma Delta T Cells: Report on a Series of Healthy Caucasian Portuguese Adults and Comprehensive Review of the Literature

Gamma delta T cells (Tc) are divided according to the type of Vδ and Vγ chains they express, with two major γδ Tc subsets being recognized in humans: Vδ2Vγ9 and Vδ1. Despite many studies in pathological conditions, only a few have quantified the γδ Tc subsets in healthy adults, and a comprehensive review of the factors influencing its representation in the blood is missing. Here we quantified the total γδ Tc and the Vδ2/Vγ9 and Vδ1 Tc subsets in the blood from 30 healthy, Caucasian, Portuguese adults, we characterized their immunophenotype by 8-color flow cytometry, focusing in a few relevant Tc markers (CD3/TCR-γδ, CD5, CD8), and costimulatory (CD28), cytotoxic (CD16) and adhesion (CD56) molecules, and we examined the impacts of age and gender. Additionally, we reviewed the literature on the influences of race/ethnicity, age, gender, special periods of life, past infections, diet, medications and concomitant diseases on γδ Tc and their subsets. Given the multitude of factors influencing the γδ Tc repertoire and immunophenotype and the high variation observed, caution should be taken in interpreting “abnormal” γδ Tc values and repertoire deviations, and the clinical significance of small populations of “phenotypically abnormal” γδ Tc in the blood.

CCR6-Positive γδ T Cells Provide Protection Against Intracorneal HSV-1 Infection

Purpose

γδ T cells offer an important early immune defense against many different pathogens, both bacterial and viral. Herein, we examined the capacity of γδ T cell subsets to provide protection in the cornea against herpes simplex virus-1 (HSV-1).

Methods

C57Bl/6 (wild-type [WT]), γδ T-cell deficient (TCRδ-/-) and CCR6-deficient (CCR6-/-) mice were infected intracorneally with HSV-1. At multiple time points following infection, corneas were excised, and cells were immunostained for surface markers, intracellular cytokines, and analyzed using flow cytometry. WT and CCR6-/- γδ T cells were adoptively transferred into TCRδ-/- mice and corneal scores and survival were measured.

Results

Intracorneal infection of mice lacking γδ T cells exhibited increased corneal opacity scores, elevated viral titers, and higher mortality compared with WT mice. Both CCR6+ and CCR6neg γδ T cell subsets were observed in corneas after virus infection. CCR6+ γδ T cells produced IL-17A and were predominantly CD44+CD62L+, consistent with natural IL-17+ γδ T cells. In contrast IL-17A production by CCR6neg γδ T cells was infrequent, and this subset was largely single positive for CD62L or CD44. The CCR6+ subset appeared to provide protection against HSV-1 as follows: (1) CCR6-/- mice had more severe corneal opacity compared with WT mice; and (2) adoptive transfer of γδ T cells from WT mice restored protection in TCRδ-/- mice whereas transfer of γδ T cells from CCR6-/- mice did not.

Conclusions

γδ T cells in the cornea can be divided into CCR6+ and CCR6neg subsets with the former conferring protection early after intracorneal HSV-1 infection.

Vaccines for Herpes Simplex: Recent Progress Driven by Viral and Adjuvant Immunology

Herpes simplex viruses (HSV) types 1 and 2 are ubiquitous. They both cause genital herpes, occasionally severe disease in the immunocompromised, and facilitate much HIV acquisition globally. Despite more than 60 years of research, there is no licensed prophylactic HSV vaccine and some doubt as to whether this can be achieved. Nevertheless, a previous HSV vaccine candidate did have partial success in preventing genital herpes and HSV acquisition and another immunotherapeutic candidate reduced viral shedding and recurrent lesions, inspiring further research. However, the entry pathway of HSV into the anogenital mucosa and the subsequent cascade of immune responses need further elucidation so that these responses could be mimicked or improved by a vaccine, to prevent viral entry and colonization of the neuronal ganglia. For an effective novel vaccine against genital herpes the choice of antigen and adjuvant may be critical. The incorporation of adjuvants of the vaccine candidates in the past, may account for their partial efficacy. It is likely that they can be improved by understanding the mechanisms of immune responses elicited by different adjuvants and comparing these to natural immune responses. Here we review the history of vaccines for HSV, those in development and compare them to successful vaccines for chicken pox or herpes zoster. We also review what is known of the natural immune control of herpes lesions, via interacting innate immunity and CD4 and CD8 T cells and the lessons they provide for development of new, more effective vaccines.

Mechanisms of Immune Control of Mucosal HSV Infection: A Guide to Rational Vaccine Design

Herpes Simplex Virus (HSV) is a highly prevalent sexually transmitted infection that aside from causing cold sores and genital lesions, causes complications in the immunocompromised and has facilitated a large proportion of HIV acquisition globally. Despite decades of research, there is no prophylactic HSV vaccine ready for use in humans, leaving many questioning whether a prophylactic vaccine is an achievable goal. A previous HSV vaccine trial did have partial success in decreasing acquisition of HSV2–promising evidence that vaccines can prevent acquisition. However, there is still an incomplete understanding of the immune response pathways elicited by HSV after initial mucosal infection and how best to replicate these responses with a vaccine, such that acquisition and colonization of the dorsal root ganglia could be prevented. Another factor to consider in the rational design of an HSV vaccine is adjuvant choice. Understanding the immune responses elicited by different adjuvants and whether lasting humoral and cell-mediated responses are induced is important, especially when studies of past trial vaccines found that a sufficiently protective cell-mediated response was lacking. In this review, we discuss what is known of the immune control involved in initial herpes lesions and reactivation, including the importance of CD4 and CD8 T cells, and the interplay between innate and adaptive immunity in response to primary infection, specifically focusing on the viral relay involved. Additionally, a summary of previous and current vaccine trials, including the components used, immune responses elicited and the feasibility of prophylactic vaccines looking forward, will also be discussed.

Dok-1 and Dok-2 Are Required To Maintain Herpes Simplex Virus 1-Specific CD8+ T Cells in a Murine Model of Ocular Infection

Dok-1 and Dok-2 negatively regulate responses downstream of several immune receptors in lymphoid and myeloid cells. Recent evidence showed that Dok proteins are essential in the formation of memory CD8⁺ T cells to an exogenous epitope expressed by vaccinia virus; however, the importance of Dok-1 and Dok-2 in the control of viral infection is unknown. Here, we investigated the role of Dok proteins in modulating the immune response against herpes simplex virus 1 (HSV-1) in a mouse model of ocular infection. During acute infection, viral titers in the eye were similar in wild-type (WT) and Dok-1 and Dok-2 double-knockout (DKO) mice, and the percentages of infiltrating leukocytes were similar in DKO and WT corneas and trigeminal ganglia (TG). DKO mice exhibited a diminished CD8⁺ T cell response to the immunodominant HSV-1 glycoprotein B (gB) epitope in the spleen and draining lymph nodes compared to WT mice during acute infection. Remarkably, gB-specific CD8⁺ T cells almost completely disappeared in the spleens of DKO mice during latency, and the reduction of CD8⁺ effector memory T (Tem) cells was more severe than that of CD8⁺ central memory T (Tcm) cells. The percentage of gB-specific CD8⁺ T cells in TG during latency was also dramatically reduced in DKO mice; however, they were phenotypically similar to those from WT mice. In ex vivo assays, reactivation was detected earlier in TG cultures from infected DKO versus WT mice. Thus, Dok-1 and Dok-2 promote survival of gB-specific CD8⁺ T cells in TG latently infected with HSV-1.IMPORTANCE HSV-1 establishes lifelong latency in sensory neurons of trigeminal ganglia (TG). In humans, HSV-1 is able to sporadically reactivate from latently infected neurons and establish a lytic infection at a site to which the neurons project. Most herpetic disease in humans is due to reactivation of HSV-1 from latency rather than to primary acute infection. CD8⁺ T cells are thought to play an important role in controlling recurrent infections. In this study, we examined the involvement of Dok-1 and Dok-2 signaling proteins in the control of HSV-1 infection. We provide evidence that Dok proteins are required to maintain a CD8⁺ T cell response against HSV-1 during latency-especially CD8⁺ Tem cells-and that they negatively affect HSV-1 reactivation from latency. Elucidating Dok-mediated mechanisms involved in the control of HSV-1 reactivation from latency might contribute to the development of therapeutic strategies to prevent recurrent HSV-1-induced pathology.

γδ T Cell-Mediated Immunity to Cytomegalovirus Infection

γδ T lymphocytes are unconventional immune cells, which have both innate- and adaptive-like features allowing them to respond to a wide spectrum of pathogens. For many years, we and others have reported on the role of these cells in the immune response to human cytomegalovirus in transplant patients, pregnant women, neonates, immunodeficient children, and healthy people. Indeed, and as described for CD8+ T cells, CMV infection leaves a specific imprint on the γδ T cell compartment: (i) driving a long-lasting expansion of oligoclonal γδ T cells in the blood of seropositive individuals, (ii) inducing their differentiation into effector/memory cells expressing a TEMRA phenotype, and (iii) enhancing their antiviral effector functions (i.e., cytotoxicity and IFNγ production). Recently, two studies using murine CMV (MCMV) have corroborated and extended these observations. In particular, they have illustrated the ability of adoptively transferred MCMV-induced γδ T cells to protect immune-deficient mice against virus-induced death. In vivo, expansion of γδ T cells is associated with the clearance of CMV infection as well as with reduced cancer occurrence or leukemia relapse risk in kidney transplant patients and allogeneic stem cell recipients, respectively. Taken together, all these studies show that γδ T cells are important immune effectors against CMV and cancer, which are life-threatening diseases affecting transplant recipients. The ability of CMV-induced γδ T cells to act independently of other immune cells opens the door to the development of novel cellular immunotherapies that could be particularly beneficial for immunocompromised transplant recipients.

Elevated PrPC Expression Predisposes to Increased HSV-1 Pathogenicity

PrPC is a ubiquitously expressed glycophos-phatidylinositol-linked cell-surface glycoprotein found primarily in neural tissue. Although its normal function has not been established, there is evidence suggesting that PrPC is involved in cell signalling and cellular homeostasis. This suggests that variation in neuronal expression levels of this protein contributes towards pathogenicity induced by neurotropic agents. We have investigated the pathological response to infection with herpes simplex virus type-1 (HSV-1) in strains of mice that express different levels of PrPC. Prnp−/− mice fail to express PrPC due to an interruption in the open reading frame of the Prnp gene, whilst tg19 and tga20 mice express approximately 5 and 10 times more PrPC protein, respectively, than wild-type animals. Mice that express normal or increased levels of PrPC protein were more susceptible to acute HSV-1 infection than Prnp−/− mice. Following ear pinna inoculation with HSV-1 SC16, the order of susceptibility was tga20>tg19>wild-type> Prnp−/−. This trend was reversed when latent virus was assessed. Prnp−/− mice expressed significantly higher levels of latency-associated transcript-positive neurons in various tissues when compared with wild-type, tg19 and tga20 mice. Collectively, our data show that acute HSV-1 replication proceeds more efficiently in neuronal tissue that expresses PrPC protein and lends support to the view that this protein is involved in regulation of neurotropic viral pathogenesis. This suggests that interference of PrPC expression, or possible biochemical pathways associated with its function, may serve as an effective means of limiting the pathogenesis of acute HSV-1 infection.

Effector γδ T Cell Differentiation Relies on Master but Not Auxiliary Th Cell Transcription Factors

γδ T lymphocytes are programmed into distinct IFN-γ-producing CD27(+) (γδ27(+)) and IL-17-producing CD27(-) (γδ27(-)) subsets that play key roles in protective or pathogenic immune responses. Although the signature cytokines are shared with their αβ Th1 (for γδ27(+)) and Th17 (for γδ27(-)) cell counterparts, we dissect in this study similarities and differences in the transcriptional requirements of murine effector γδ27(+), γδ27(-)CCR6(-), and γδ27(-)CCR6(+) γδ T cell subsets and αβ T cells. We found they share dependence on the master transcription factors T-bet and RORγt for IFN-γ and IL-17 production, respectively. However, Eomes is fully dispensable for IFN-γ production by γδ T cells. Furthermore, the Th17 cell auxiliary transcription factors RORα and BATF are not required for IL-17 production by γδ27(-) cell subsets. We also show that γδ27(-) (but not γδ27(+)) cells become polyfunctional upon IL-1β plus IL-23 stimulation, cosecreting IL-17A, IL-17F, IL-22, GM-CSF, and IFN-γ. Collectively, our in vitro and in vivo data firmly establish the molecular segregation between γδ27(+) and γδ27(-) T cell subsets and provide novel insight on the nonoverlapping transcriptional networks that control the differentiation of effector γδ versus αβ T cell subsets.

The Role of γδ T Cells in Systemic Lupus Erythematosus

Systemic lupus erythematosus (SLE) is an autoimmune disease that is characterized by the overproduction of autoantibodies against an array of nuclear and cytoplasmic antigens and affects multiple organs, such as the skin, joints, kidneys, and neuronal tissues. T cells have been recognized as important players in the development of SLE due to their functions in cytokine secretion, antigen presentation, and supporting B cells for antibody production. γδ T cells are a minor population of T cells that play important roles in infection and tumor-associated disease. In recent years, the role of γδ T cells in autoimmune diseases has been investigated. In this review, we discussed the role of γδ T cells in the pathogenesis of SLE.

γδ T Cell-Dependent Regulatory T Cells Prevent the Development of Autoimmune Keratitis

To prevent potentially damaging inflammatory responses, the eye actively promotes local immune tolerance via a variety of mechanisms. Owing to trauma, infection, or other ongoing autoimmunity, these mechanisms sometimes fail, and an autoimmune disorder may develop in the eye. In mice of the C57BL/10 (B10) background, autoimmune keratitis often develops spontaneously, particularly in the females. Its incidence is greatly elevated in the absence of γδ T cells, such that ∼80% of female B10.TCRδ(-/-) mice develop keratitis by 18 wk of age. In this article, we show that CD8(+) αβ T cells are the drivers of this disease, because adoptive transfer of CD8(+), but not CD4(+), T cells to keratitis-resistant B10.TCRβ/δ(-/-) hosts induced a high incidence of keratitis. This finding was unexpected because in other autoimmune diseases, more often CD4(+) αβ T cells, or both CD4(+) and CD8(+) αβ T cells, mediate the disease. Compared with wild-type B10 mice, B10.TCRδ(-/-) mice also show increased percentages of peripheral memory phenotype CD8(+) αβ T cells, along with an elevated frequency of CD8(+) αβ T cells biased to produce inflammatory cytokines. In addition, B10.TCRδ-/- mice have fewer peripheral CD4(+) CD25(+) Foxp3(+) αβ regulatory T cells (Tregs), which express lower levels of receptors needed for Treg development and function. Together, these observations suggest that in B10 background mice, γδ T cells are required to generate adequate numbers of CD4(+) CD25(+) Foxp3(+) Tregs, and that in B10.TCRδ(-/-) mice a Treg deficiency allows dysregulated effector or memory CD8(+) αβ T cells to infiltrate the cornea and provoke an autoimmune attack.

Daclizumab reverses intrathecal immune cell abnormalities in multiple sclerosis

Objective

Novel treatments such as natalizumab and fingolimod achieve their therapeutic efficacy in multiple sclerosis (MS) by blocking access of subsets of immune cells into the central nervous system, thus creating nonphysiological intrathecal immunity. In contrast, daclizumab, a humanized monoclonal antibody against the alpha chain of the IL-2 receptor, has a unique mechanism of action with multiple direct effects on innate immunity. As cellular intrathecal abnormalities corresponding to MS have been well defined, we asked how daclizumab therapy affects these immunological hallmarks of the MS disease process.

Methods

Nineteen subpopulations of immune cells were assessed in a blinded fashion in the blood and 50-fold concentrated cerebrospinal fluid (CSF) cell pellet in 32 patients with untreated relapsing-remitting MS (RRMS), 22 daclizumab-treated RRMS patients, and 11 healthy donors (HDs) using 12-color flow cytometry.

Results

Long-term daclizumab therapy normalized all immunophenotyping abnormalities differentiating untreated RRMS patients from HDs. Specifically, strong enrichment of adaptive immune cells (CD4+ and CD8+ T cells and B cells) in the CSF was reversed. Similarly, daclizumab controlled MS-related increases in the innate lymphoid cells (ILCs) and lymphoid tissue inducer cells in the blood and CSF, and reverted the diminished proportion of intrathecal monocytes. The only marker that distinguished daclizumab-treated MS patients from HDs was the expansion of immunoregulatory CD56^bright NK cells.

Interpretation

Normalization of immunological abnormalities associated with MS by long-term daclizumab therapy suggests that this drug's effects on ILCs, NK cells, and dendritic cell-mediated antigen presentation to CD4+ and CD8+ T cells are critical in regulating the MS disease process.

γδ T cells confer protection against murine cytomegalovirus (MCMV)

Cytomegalovirus (CMV) is a leading infectious cause of morbidity in immune-compromised patients. γδ T cells have been involved in the response to CMV but their role in protection has not been firmly established and their dependency on other lymphocytes has not been addressed. Using C57BL/6 αβ and/or γδ T cell-deficient mice, we here show that γδ T cells are as competent as αβ T cells to protect mice from CMV-induced death. γδ T cell-mediated protection involved control of viral load and prevented organ damage. γδ T cell recovery by bone marrow transplant or adoptive transfer experiments rescued CD3ε^−/− mice from CMV-induced death confirming the protective antiviral role of γδ T cells. As observed in humans, different γδ T cell subsets were induced upon CMV challenge, which differentiated into effector memory cells. This response was observed in the liver and lungs and implicated both CD27⁺ and CD27⁻ γδ T cells. NK cells were the largely preponderant producers of IFNγ and cytotoxic granules throughout the infection, suggesting that the protective role of γδ T cells did not principally rely on either of these two functions. Finally, γδ T cells were strikingly sufficient to fully protect Rag^−/−γc^−/− mice from death, demonstrating that they can act in the absence of B and NK cells. Altogether our results uncover an autonomous protective antiviral function of γδ T cells, and open new perspectives for the characterization of a non classical mode of action which should foster the design of new γδ T cell based therapies, especially useful in αβ T cell compromised patients.

γδ T cells are unconventional T lymphocytes that play a unique role in host protection against pathogens. Human Cytomegalovirus (HCMV) is a widespread virus that can cause severe organ disease such as hepatitis and pneumonitis in immune-compromised patients. Our decade-long study conveys compelling evidence for the implication of human γδ T cells in the immune response against HCMV, but their protective role could not be formally demonstrated in humans. In the present study we use the murine model of CMV infection which allows the spatial and temporal analysis of viral spread and anti-viral immune responses. We show that, in the absence of αβ T cells, γδ T cells control MCMV-induced hepatitis, pneumonitis and death by restricting viral load in the liver, lungs and spleen. γδ T cells expand in these organs and display memory features that could be further incorporated into vaccination strategies. In conclusion, γδ T cells represent an important arm in the immune response against CMV infection that could be particularly important in the context of αβ T cell immune-suppression.

Zoledronic acid causes γδ T cells to target monocytes and down-modulate inflammatory homing

Zoledronic acid (ZA) is a potential immunotherapy for cancer because it can induce potent γδ T-cell-mediated anti-tumour responses. Clinical trials are testing the efficacy of intravenous ZA in cancer patients; however, the effects of systemic ZA on the activation and migration of peripheral γδ T cells remain poorly understood. We found that γδ T cells within ZA-treated peripheral blood mononuclear cells were degranulating, as shown by up-regulated expression of CD107a/b. Degranulation was monocyte dependent because CD107a/b expression was markedly reduced in the absence of CD14(+) cells. Consistent with monocyte-induced degranulation, we observed γδ T-cell-dependent induction of monocyte apoptosis, as shown by phosphatidylserine expression on monocytes and decreased percentages of monocytes in culture. Despite the prevailing paradigm that ZA promotes tumour homing in γδ T cells, we observed down-modulation of their tumour homing capacity, as shown by decreased expression of the inflammatory chemokine receptors CCR5 and CXCR3, and reduced migration towards the inflammatory chemokine CCL5. Taken together our data suggest that ZA causes γδ T cells to target monocytes and down-modulate the migratory programme required for inflammatory homing. This study provides novel insight into how γδ T cells interact with monocytes and the possible implications of systemic use of ZA in cancer.

Role of gamma-delta (γδ) T cells in autoimmunity

γδ T cells represent a small population of overall T lymphocytes (0.5-5%) and have variable tissue distribution in the body. γδ T cells can perform complex functions, such as immune surveillance, immunoregulation, and effector function, without undergoing clonal expansion. Heterogeneous distribution and anatomic localization of γδ T cells in the normal and inflamed tissues play an important role in alloimmunity, autoimmunity, or immunity. The cross-talk between γδ T cells and other immune cells and phenotypic and functional plasticity of γδ T cells have been given recent attention in the field of immunology. In this review, we discussed the cellular and molecular interaction of γδ T cells with other immune cells and its mechanism in the pathogenesis of various autoimmune diseases.

Role of Fas/FasL signaling in regulation of anti-viral response during HSV-2 vaginal infection in mice

Fas receptor-Fas ligand (FasL) signaling is involved in apoptosis of virus-infected cells but increasing evidence accumulates on Fas receptor as a mediator of apoptosis-independent processes such as induction of activating and pro-inflammatory signals. In this study, we examined the role of Fas/FasL pathway in regulation of anti-viral response to genital HSV-2 infection using a murine model of HSV-2 infection applied to C57BL6/J, B6. MRL-Faslpr/J and B6Smn.C3-Faslgld/J mice. HSV-2 infection of Fas- and FasL-deficient mice led to decreased migration of IFN-γ expressing NK cells and CD4+ T cells, but not of γδ T cells, into the vaginal tissue. The vaginal tissues of HSV-2 infected Fas- and FasL-deficient mice showed increased production of IL-10, followed by low expression of the early CD69 activation marker on CD4+ and CD8+ T cells and increased numbers of regulatory T cells (Tregs). Experiments in co-cultures of CD4+ T cells and bone marrow derived dendritic cells showed that lack of bilateral Fas-FasL signaling led to expansion of Tregs and increased production of IL-10 and TGF-β1. Our results demonstrate that Fas/FasL can regulate development of tolerogenic dendritic cells and expansion of Tregs early during HSV-2 infection, which further influences effective anti-viral response.

Insights into the Relationship between Toll Like Receptors and Gamma Delta T Cell Responses

The tumor microenvironment is an important aspect of cancer biology that contributes to tumor initiation, tumor progression and responses to therapy. The composition and characteristics of the tumor microenvironment vary widely and are important in determining the anti-tumor immune response. Successful immunization requires activation of both innate and adaptive immunity. Generally, immune system is compromised in patients with cancer due to immune suppression, loss of tumor antigen expression and dysfunction of antigen presenting cells (APC). Thus, therapeutic immunization leading to cancer regression remains a significant challenge. Certain cells of the immune system, including dendritic cells (DCs) and gamma delta (γδ) T cells are capable of driving potent anti-tumor responses. The property of MHC-unrestricted cytotoxicity, high potential of cytokine release, tissue tropism and early activation in infections and malignant disease makes γδ T cells as an emerging candidate for immunotherapy. Various strategies are being developed to enhance anti-tumor immune responses of γδ T cells and DCs one of them is the use of novel adjuvants like toll like receptors (TLR) agonists, which enhance γδ T cell function directly or through DC activation, which has ability to prime γδ T cells. TLR agonists are being used clinically either alone or in combination with tumor antigens and has shown initial success in both enhancing immune responses and eliciting anti-tumor activity. TLR activated γδ T cells and DCs nurture each other's activation. This provides a potent base for first line of defense and manipulation of the adaptive response against pathogens and cancer. The available data provides a strong rationale for initiating combinatorial therapy for the treatment of diseases and this review will summarize the application of adjuvants (TLRs) for boosting immune response of γδ T cells to treat cancer and infectious diseases and their use in combinatorial therapy.

Microglia-induced IL-6 protects against neuronal loss following HSV-1 infection of neural progenitor cells

Herpes virus type 1 (HSV-1) is one of the most widespread human pathogens and accounts for more than 90% of cases of herpes simplex encephalitis (HSE) causing severe and permanent neurologic sequelae among surviving patients. We hypothesize such CNS deficits are due to HSV-1 infection of neural progenitor cells (NPCs). In vivo, HSV-1 infection was found to diminish NPC numbers in the subventricular zone. Upon culture of NPCs in conditions that stimulate their differentiation, we found HSV-1 infection of NPCs resulted in the loss of neuronal precursors with no significant change in the percentage of astrocytes or oligodendrocytes. We propose this is due a direct effect of HSV-1 on neuronal survival without alteration of the differentiation process. The neuronal loss was prevented by the addition of microglia or conditioned media from NPC/microglia co-cultures. Using neutralizing antibodies and recombinant cytokines, we identified interleukin-6 (IL-6) as responsible for the protective effect by microglia, likely through its downstream Signal Transducer and Activator of Transcription 3 (STAT3) cascade.

Role of natural killer and Gamma-delta T cells in West Nile virus infection

Natural Killer (NK) cells and Gamma-delta T cells are both innate lymphocytes that respond rapidly and non-specifically to viral infection and other pathogens. They are also known to form a unique link between innate and adaptive immunity. Although they have similar immune features and effector functions, accumulating evidence in mice and humans suggest these two cell types have distinct roles in the control of infection by West Nile virus (WNV), a re-emerging pathogen that has caused fatal encephalitis in North America over the past decade. This review will discuss recent studies on these two cell types in protective immunity and viral pathogenesis during WNV infection.

Differential chemokine and cytokine production by neonatal bovine γδ T-cell subsets in response to viral toll-like receptor agonists and in vivo respiratory syncytial virus infection

γδ T cells respond to stimulation via toll-like receptors (TLR). Bovine γδ T cells express TLR3 and TLR7, receptors that are key for the recognition of viruses such as bovine respiratory syncytial virus (BRSV); however, responses of γδ T cells to stimulation via these receptors, and their role during viral infections, remains unclear. Here, we demonstrate that neonatal bovine γδ T cells exhibit robust chemokine and cytokine production in response to the TLR3 agonist, Poly(I:C), and the TLR7 agonist, Imiquimod. Importantly, we observe a similar phenotype in γδ T-cell subsets purified from calves infected with BRSV. Bovine γδ T cells are divided into subsets based upon their expression of WC1, and the response to TLR stimulation and viral infection differs between these subsets, with WC1.1(+) and WC1(neg) γδ T cells producing macrophage inflammatory protein-1α and granulocyte-macrophage colony-stimulating factor, and WC1.2(+) γδ T cells preferentially producing the regulatory cytokines interleukin-10 and transforming growth factor-β. We further report that the active vitamin D metabolite 1,25-dihydroxyvitamin D3 does not alter γδ T-cell responses to TLR agonists or BRSV. To our knowledge, this is the first characterization of the γδ T-cell response during in vivo BRSV infection and the first suggestion that WC1.1(+) and WC1(neg) γδ T cells contribute to the recruitment of inflammatory populations during viral infection. Based on our results, we propose that circulating γδ T cells are poised to rapidly respond to viral infection and suggest an important role for γδ T cells in the innate immune response of the bovine neonate.

Tripartite immune cell co-operation in the Bacillus Calmette Guérin-induced activation of γδ T cells

γδ T cells contribute to immunosurveillance of pathogenic infections and malignant transformations; however, mechanisms of activation have yet to be fully defined. In this study we demonstrate a novel mechanism by which human Vδ2(+) γδ T cells are activated by the model pathogen Bacillus Calmette Guérin (BCG). We show in vitro that Vδ2 cell cytokine production and cytotoxic activity in response to BCG are dependent on both dendritic cells (DCs) and memory CD4(+) αβ T cells (CD4 T cells). We found that Vδ2 cells are indirectly activated by BCG in an interleukin (IL)-12p70-dependent manner, and that DC production of the IL-12p70 responsible for Vδ2 cell activation requires Toll-like receptor 2/4 ligands from BCG and interferon (IFN)-γ from memory CD4 T cells. Our data suggest that Vδ2 cell responses to BCG are dependent on the activation of IFN-γ-producing memory CD4 T cells, and provide novel insight into the complex interplay between cells of the innate and adaptive immune response.

Microglia and a functional type I IFN pathway are required to counter HSV-1-driven brain lateral ventricle enlargement and encephalitis

HSV-1 is the leading cause of sporadic viral encephalitis, with mortality rates approaching 30% despite treatment with the antiviral drug of choice, acyclovir. Permanent neurologic deficits are common in patients that survive, but the mechanism leading to this pathology is poorly understood, impeding clinical advancements in treatment to reduce CNS morbidity. Using magnetic resonance imaging and type I IFN receptor-deficient mouse chimeras, we demonstrate HSV-1 gains access to the murine brain stem and subsequently brain ependymal cells, leading to enlargement of the cerebral lateral ventricle and infection of the brain parenchyma. A similar enlargement in the lateral ventricles is found in a subpopulation of herpes simplex encephalitic patients. Associated with encephalitis is an increase in CXCL1 and CXCL10 levels in the cerebral spinal fluid, TNF-α expression in the ependymal region, and the influx of neutrophils of encephalitic mouse brains. Reduction in lateral ventricle enlargement using anti-secretory factor peptide 16 reduces mortality significantly in HSV-1-infected mice without any effect on expression of inflammatory mediators, infiltration of leukocytes, or changes in viral titer. Microglial cells but not infiltrating leukocytes or other resident glial cells or neurons are the principal source of resistance in the CNS during the first 5 d postinfection through a Toll/IL-1R domain-containing adapter inducing IFN-β-dependent, type I IFN pathway. Our results implicate lateral ventricle enlargement as a major cause of mortality in mice and speculate such an event transpires in a subpopulation of human HSV encephalitic patients.

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

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

Diversity of γδ T-cell antigens

In the last two decades, it has become clear that γδ T cells recognize a diverse array of antigens including self and foreign, large and small, and peptidic and non-peptidic molecules. In this respect, γδ antigens as a whole resemble more the antigens recognized by antibodies than those recognized by αβ T cells. Because of this antigenic diversity, no single mechanism-such as the major histocompatibility complex (MHC) restriction of αβ T cells-is likely to provide a basis for all observed T-cell antigen receptor (TCR)-dependent γδ T-cell responses. Furthermore, available evidence suggests that many individual γδ T cells are poly-specific, probably using different modes of ligand recognition in their responses to unrelated antigens. While posing a unique challenge in the maintenance of self-tolerance, this broad reactivity pattern might enable multiple overlapping uses of γδ T-cell populations, and thus generate a more efficient immune response.

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.

Herpes keratitis

Herpes simplex virus-1 (HSV-1) infects the majority of the world's population. These infections are often asymptomatic, but ocular HSV-1 infections cause multiple pathologies with perhaps the most destructive being herpes stromal keratitis (HSK). HSK lesions, which are immunoinflammatory in nature, can recur throughout life and often cause progressive corneal scaring resulting in visual impairment. Current treatment involves broad local immunosuppression with topical steroids along with antiviral coverage. Unfortunately, the immunopathologic mechanisms defined in animal models of HSK have not yet translated into improved therapy. Herein, we review the clinical epidemiology and pathology of the disease and summarize the large amount of basic research regarding the immunopathology of HSK. We examine the role of the innate and adaptive immune system in the clearance of virus and the destruction of the normal corneal architecture that is typical of HSK. Our goal is to define current knowledge of the pathogenic mechanisms and recurrent nature of HSK and identify areas that require further study.

αβ TCR⁺ T cells, but not B cells, promote autoimmune keratitis in b10 mice lacking γδ T cells

PURPOSE

To investigate additional factors in the spontaneous development of keratitis previously reported in B10.TCRδ⁻/⁻ female mice.

METHODS

The study tested whether susceptible B10.TCRδ⁻/⁻ mice have dry eyes compared with resistant B6.TCRδ⁻/⁻ females and also rederived the B10.TCRδ⁻/⁻ strain to test for the role of an infectious agent. Also assessed was whether adoptive transfer of αβ T cells from autoimmune mice induced keratitis in resistant mice. In addition, a potential role was examined for B cells or autoantibodies by B-cell inactivation, and the role of female hormones was tested by ovariectomy. Finally, the study investigated whether adoptive transfer of Vγ1⁺ γδ T cells confers protection.

RESULTS

Tear production in B10.TCRδ⁻/⁻ females was actually higher than in B6.TCRδ⁻/⁻ controls. Rederived B10.TCRδ⁻/⁻ mice still developed keratitis. Keratitis was induced in resistant mice after adoptive transfer of αβ T cells from keratitic donors. Inactivation of B cells from susceptible mice had no effect on the development of keratitis. Ovariectomy did not significantly reduce disease in B10.TCRδ⁻/⁻ females. Adoptive transfer of Vγ1⁺ cells from wild-type donors reduced keratitis in B10.TCRδ⁻/⁻ females.

CONCLUSIONS

Neither low tear levels nor ovarian hormones contribute to spontaneous keratitis in B10.TCRδ⁻/⁻ female mice, nor does it appear to depend on an infectious agent carried vertically in this strain. However, αβ T cells from keratitic hosts are sufficient to induce disease in the resistant B10.TCRβ⁻/⁻δ⁻/⁻ strain. Autoaggressive αβ T cells in the absence of Vγ1⁺ T cells in B10.TCRδ⁻/⁻ mice may be insufficiently checked to prevent disease.

Early responding dendritic cells direct the local NK response to control herpes simplex virus 1 infection within the cornea

Dendritic cells (DCs) regulate both innate and adaptive immune responses. In this article, we exploit the unique avascularity of the cornea to examine a role for local or very early infiltrating DCs in regulating the migration of blood-derived innate immune cells toward HSV-1 lesions. A single systemic diphtheria toxin treatment 2 d before HSV-1 corneal infection transiently depleted CD11c(+) DCs from both the cornea and lymphoid organs of CD11c-DTR bone marrow chimeric mice for up to 24 h postinfection. Transient DC depletion significantly delayed HSV-1 clearance from the cornea through 6 d postinfection. No further compromise of viral clearance was observed when DCs were continuously depleted throughout the first week of infection. DC depletion did not influence extravasation of NK cells, inflammatory monocytes, or neutrophils into the peripheral cornea, but it did significantly reduce migration of NK cells and inflammatory monocytes, but not neutrophils, toward the HSV-1 lesion in the central cornea. Depletion of NK cells resulted in similar loss of viral control to transient DC ablation. Our findings demonstrate that resident corneal DCs and/or those that infiltrate the cornea during the first 24 h after HSV-1 infection contribute to the migration of NK cells and inflammatory monocytes into the central cornea, and are consistent with a role for NK cells and possibly inflammatory monocytes, but not polymorphonuclear neutrophils, in clearing HSV-1 from the infected cornea.

Role of γδ T cells in West Nile virus-induced encephalitis: friend or foe?

West Nile virus (WNV)-induced encephalitis has been a public health concern in North America over the past decade. No therapeutics or vaccines are available for human use. Studies in animal models have provided important information for investigations of WNV pathogenesis and the host immune response in humans. This article will give an overview of the role of γδ T cells, one of the non-classical T cell subsets in the murine model of WNV encephalitis.

Modulation of γδ T cell responses by TLR ligands

Toll-like receptors (TLR) are pattern-recognition receptors that recognize a broad variety of structurally conserved molecules derived from microbes. The recognition of TLR ligands functions as a primary sensor of the innate immune system, leading to subsequent indirect activation of the adaptive immunity as well as none-immune cells. However, TLR are also expressed by several T cell subsets, and the respective ligands can directly modulate their effector functions. The present review summarizes the recent findings of γδ T cell modulation by TLR ligands. TLR1/2/6, 3, and 5 ligands can act directly in combination with T cell receptor (TCR) stimulation to enhance cytokine/chemokine production of freshly isolated human γδ T cells. In contrast to human γδ T cells, murine and bovine γδ T cells can directly respond to TLR2 ligands with increased proliferation and cytokine production in a TCR-independent manner. Indirect stimulatory effects on IFN-γ production of human and murine γδ T cells via TLR-ligand activated dendritic cells have been described for TLR2, 3, 4, 7, and 9 ligands. In addition, TLR3 and 7 ligands indirectly increase tumor cell lysis by human γδ T cells, whereas ligation of TLR8 abolishes the suppressive activity of human tumor-infiltrating Vδ1 γδ T cells on αβ T cells and dendritic cells. Taken together, these data suggest that TLR-mediated signals received by γδ T cells enhance the initiation of adaptive immune responses during bacterial and viral infection directly or indirectly. Moreover, TLR ligands enhance cytotoxic tumor responses of γδ T cells and regulate the suppressive capacity of γδ T cells.

The Role of Plasmacytoid Dendritic Cells in Innate and Adaptive Immune Responses against Alpha Herpes Virus Infections

In 1999, two independent groups identified plasmacytoid dendritic cells (PDC) as major type I interferon- (IFN-) producing cells in the blood. Since then, evidence is accumulating that PDC are a multifunctional cell population effectively coordinating innate and adaptive immune responses. This paper focuses on the role of different immune cells and their interactions in the surveillance of alpha herpes virus infections, summarizes current knowledge on PDC surface receptors and their role in direct cell-cell contacts, and develops a risk factor model for the clinical implications of herpes simplex and varicella zoster virus reactivation. Data from studies involving knockout mice and cell-depletion experiments as well as human studies converge into a "spider web", in which the direct and indirect crosstalk between many cell populations tightly controls acute, latent, and recurrent alpha herpes virus infections. Notably, cells involved in innate immune regulations appear to shape adaptive immune responses more extensively than previously thought.

Rapid and transient activation of γδ T cells to IFN-γ production, NK cell-like killing, and antigen processing during acute virus infection

γδ T cells are the majority peripheral blood T cells in young cattle. The role of γδ T cells in innate responses against infection with foot-and-mouth disease virus was analyzed on consecutive 5 d following infection. Before infection, bovine WC1(+) γδ T cells expressed a nonactivated phenotype relative to CD62L, CD45RO, and CD25 expression and did not produce IFN-γ ex vivo. Additionally, CD335 expression was lacking and no spontaneous target cell lysis could be detected in vitro, although perforin was detectable at a very low level. MHC class II and CD13 expression were also lacking. Following infection with foot-and-mouth disease virus, expression of CD62L and CD45RO was greatly reduced on WC1(+) γδ T cells, and unexpectedly, CD45RO expression did not recover. A transient increase in expression of CD25 correlated with production of IFN-γ. Expression of CD335 and production of perforin were detected on a subset of γδ T cells, and this correlated with an increased spontaneous killing of xenogeneic target cells. Furthermore, increased MHC class II expression was detected on WC1(+) γδ T cells, and these cells processed protein Ags. These activities are rapidly induced, within 3 d, and wane by 5 d following infection. All of these functions, NK-like killing, Ag processing, and IFN-γ production, have been demonstrated for these cells in various species. However, these results are unique in that all these functions are detected in the same samples of WC1(+) γδ T cells, suggesting a pivotal role of these cells in controlling virus infection.

Cutting edge: adaptive versus innate receptor signals selectively control the pool sizes of murine IFN-γ- or IL-17-producing γδ T cells upon infection

γδ T lymphocytes are commonly viewed as embracing properties of both adaptive and innate immunity. Contributing to this is their responsiveness to pathogen products, either with or without the involvement of the TCR and its coreceptors. This study clarifies this paradoxical behavior by showing that these two modes of responsiveness are the properties of two discrete sets of murine lymphoid γδ T cells. Thus, MyD88 deficiency severely impaired the response to malaria infection of CD27((-)), IL-17A-producing γδ T cells, but not of IFN-γ-producing γδ cells. Instead, the latter compartment was severely contracted by ablating CD27, which synergizes with TCRγδ in the induction of antiapoptotic mediators and cell cycle-promoting genes in CD27((+)), IFN-γ-secreting γδ T cells. Hence, innate versus adaptive receptors differentially control the peripheral pool sizes of discrete proinflammatory γδ T cell subsets during immune responses to infection.

Herpes simplex virus infects skin gamma delta T cells before Langerhans cells and impedes migration of infected Langerhans cells by inducing apoptosis and blocking E-cadherin downregulation

The role individual skin dendritic cell (DC) subsets play in the immune response to HSV remains unclear. We investigated the effect of HSV on DC virus uptake, viability, and migration after cutaneous infection in vitro and in vivo. HSV increased the emigration of skin DCs from whole skin explants over 3 d postinfection (p.i.) compared with mock controls, but the kinetics of emigration was influenced by the skin DC subset. Uninfected (bystander) Langerhans cells (LCs) were the major emigrant DC subset at 24 h p.i., but thereafter, large increases in infected CD103(+)langerin(+) dermal DC (dDC) and uninfected langerin(-) dDC emigration were also observed. LC infection was confirmed by the presence of HSV glycoprotein D (gD) and was associated with impaired migration from cultured skin. Langerin(+) dDC also expressed HSV gD, but infection did not impede migration. We then followed the virus in live MacGreen mice in which LCs express GFP using a fluorescent HSV-1 strain by time-lapse confocal microscopy. We observed a sequential infection of epidermal cells, first in keratinocytes and epidermal gammadelta T cells at 6 h p.i., followed by the occurrence of HSVgD(+) LCs at 24 h p.i. HSV induced CCR7 upregulation on all langerin(+) DC, including infected LCs, and increased production of skin TNF-alpha and IL-1beta. However, a large proportion of infected LCs that remained within the skin was apoptotic and failed to downregulate E-cadherin compared with bystander LCs or mock controls. Thus, HSV infection of LCs is preceded by infection of gammadelta T cells and delays migration.

Regulatory effect of gammadelta T cells on IL-17+ uveitogenic T cells

PURPOSE

To characterize the regulatory effect of gammadelta T cells in the activation of IL-17+ uveitogenic T cells.

METHODS

The authors administered the gammadelta TCR-specific antibody GL3 to B6 mice before or after antigen immunization and examined Th1- or Th17-polarized T-cell responses. The intensity of Th17 responses was also examined in responder T cells containing varying numbers of gammadelta T cells.

RESULTS

GL3 treatment resulted in varying degrees of depletion of circulating gammadelta T cells, depending on when the antibody was administered. The intensity of the alphabetaTCR+IL-17+, but not the alphabetaTCR+IFN-gamma+, IRBP-specific T-cell responses was correlated to the percentage of gammadelta T cells in the responder T cells. Kinetic studies showed that early IL-17+ T cells were primarily gammadelta T cells, with a later gradual shift to alphabeta T cells. A close association was seen between the intensity of the IL-17+ autoreactive T-cell response and the percentage of gammadelta T cells in the responder T cells. Although a modest increase in gammadelta T cells among the responder T cells promoted the expansion of IL-17+ alphabetaTCR+ T cells, a higher proportion of gammadelta T cells inhibited it.

CONCLUSIONS

gammadelta T cells are actively involved in the generation of alphabetaTCR+IL-17+ T cells. The number of gammadelta T cells and the alphabeta/gammadelta T-cell ratio in the responder T cells regulate the intensity of the Th17-type autoreactive T-cell response.

Bisphosphonates and RANK ligand inhibitors for the treatment and prevention of metastatic bone disease

Bisphosphonates (BPs) are potent inhibitors of osteoclast-mediated bone resorption, which is increased when cancer cells invade bone. BPs are an established treatment for cancer that has spread to bone, and effectively reduce pain and other skeletal-related events. New directions in metastatic bone disease (MBD) include personalised BP therapy, such as using bone markers to guide frequency of BP administration and bone targeting agents such as denosumab (AMG 162). Clinical trials strongly suggest that denosumab might play a defined role in the future management of MBD. In terms of potential anti-cancer activity, early data tentatively suggest that zoledronic acid might have a role to play in the prevention of metastatic disease, though whether this is a direct effect on cancer cells, or indirect via the bone marrow micro-environment, or both, is as yet undiscovered. The definitive answer as to the role of adjuvant BP in early cancer is being addressed, with over 20,000 patients with breast, prostate or lung cancer currently participating in adjuvant BP randomised trials. The results of these trials should be available in the next few years, and this will establish whether BPs given early in the course of cancer will be able to prevent the formation of metastases, bone or otherwise.

Human gammadelta T cell recognition of lipid A is predominately presented by CD1b or CD1c on dendritic cells

Background

The γδ T cells serve as early immune defense against certain encountered microbes. Only a few γδ T cell-recognized ligands from microbial antigens have been identified so far and the mechanisms by which γδ T cells recognize these ligands remain unknown. Here we explored the mechanism of interaction of human γδ T cells in peripheral blood with Lipid A (LA).

Results

First, resting γδ T cells (mainly Vδ2 T cells) displayed a strong proliferative response to LA-pulsed monocyte-derived dendritic cells (moDC) and LA-pulsed paraformaldehyde-fixed moDC, but not to free LA in a TCR γδ-dependent manner. Second, anti-CD1b or anti-CD1c antibodies could block proliferative response of resting γδ T cells to LA-loaded moDC. Besides, only LA-loaded CD1b/CD1c-transfected C1R lymphoblastoma cells (CD1b-/CD1c-C1R) were able to stimulate the proliferation of human γδ T cells. Third, the expressions of both Toll-like receptor (TLR)2 and TLR4 on surface of LA-activated γδ T cells were upregulated, whereas only anti-TLR4 antibody could partially block their response to LA; Finally LA-loaded moDCs induce γδ T cells to produce Th1 cytokines, such as IFN-γ.

Conclusion

Taken together, we found a novel mechanism that human γδ T cells recognize LA in a CD1b- or CD1c-restricted manner in first response against Gram-bacteria, while the interaction between TLR4 on γδ T cells and LA might strengthen the subsequent response of γδ T cells.

Reviewers

This article was reviewed by Hao Shen, Youwen He (nominated by Dr. Laurence C Eisenlohr), Dr. Michael Lenardo and Dr. Pushpa Pandiyan.

Neonates harbour highly active gammadelta T cells with selective impairments in preterm infants

Acknowledgement of the breadth of T-cell pleiotropy has provoked increasing interest in the degree to which functional responsiveness is elicited by environmental cues versus differentiation. This is particularly relevant for young animals requiring rapid responses to acute environmental exposure. In young mice, gammadelta T cells are disproportionately important for immuno-protection. To examine the situation in humans, we compared populations and clones of T cells from term and preterm babies, and adults. By comparison with alphabeta T cells, neonate-derived gammadelta cells show stronger, pleiotropic functional responsiveness, and lack signatory deficits in IFN-gamma production. Emphasising the acquisition of functional competence in utero, IFN-gamma was produced by gammadelta cells sampled from premature births, and, although one month's post-partum environmental exposure invariably increased their TNF-alpha production, it had no consistent effect on IFN-gamma or IL-2. In sum, gammadelta cells seem well positioned at birth to contribute to immuno-protection and immuno-regulation, possibly compensating for selective immaturity in the alphabeta compartment. With regard to the susceptibilities of preterm babies to viral infection, gammadelta cells from preterm neonates were commonly impaired in Toll-like receptor-3 and -7 expression and compared with cells from term babies failed to optimise cytokine production in response to coincident TCR and TLR agonists.