Role of CD4+ and CD8+ T Cells in Clearance of Primary Pulmonary Infection with Coxiella burnetii

The mechanisms of the primary adaptive immune response to Coxiella burnetii are not well known. Following inoculation of the lungs with C. burnetii Nine Mile phase I (NMI), SCID mice developed pneumonia and splenomegaly and succumbed to infection, whereas wild-type mice cleared the infection by 24 days. SCID mice reconstituted with either CD4⁺ T cells or CD8⁺ T cells alone were able to control the infection, indicating that the presence of either type of T cells was sufficient to control infection, and B cells were not necessary for primary immunity. Similarly, wild-type mice depleted of either CD4⁺ T cells or CD8⁺ T cells controlled infections in their lungs, but these mice were highly susceptible if they were depleted of both types of T cells. However, compared to CD4⁺ T-cell-dependent protection, CD8⁺ T-cell-dependent protection resulted in less inflammation in the lungs and less growth of bacteria in the spleens.Coxiella burnetii, the etiologic agent of Q fever, is thought to be a widely underdiagnosed cause of pneumonia. Acute infections with this organism commonly result in a self-limiting, febrile illness with pulmonary involvement, reflecting the typical acquisition of the infection by the aerosol route. Complications associated with such infections include development of a chronic phase in certain susceptible individuals which presents as endocarditis and has a high fatality rate in the absence of appropriate treatment. Interest in this organism has recently been piqued by its inclusion on the list of potential bioterror agents. Notwithstanding the relatively low mortality rate associated with C. burnetii infections, this organism is highly infectious and has the capacity to cause significant morbidity (16, 23).Two phase variants C. burnetii have been found; phase I is highly virulent and is the naturally occurring variant, and phase II occurs following repeated passage through cell cultures. The two phases differ in lipopolysaccharide (LPS) structure. Phase I C. burnetii encodes a complete LPS with an O side chain, while phase II C. burnetii expresses a truncated LPS lacking the O side chain and some additional sugar residues (10). Andoh et al. (2) examined the comparative virulence of the two variants in SCID and immunocompetent mice using the intraperitoneal (i.p.) route of inoculation and demonstrated that some replication of C. burnetii Nine Mile phase II (NMII) took place in immunocompromised mice but not in immunocompetent mice. This finding suggests that an acquired immune system is required for control of infection with this organism (3).Aerosols are thought to be the most common cause of transmission of Coxiella to humans and other mammals. However, very little is known about the effects of this route of infection at the cellular level. To date, most studies using animal models of C. burnetii infection have utilized the intraperitoneal (i.p.) route of inoculation, and while these studies have provided important data, this route of infection may not entirely reproduce the pulmonary sequelae of most human infections (3). Studies of pulmonary Coxiella infection in guinea pigs (15) and in BALB/c and SCID mice (21) demonstrated that lymphocytes accumulate early during primary lung infection. However, the subsets of lymphocytes elicited in the primary pulmonary response and the role of each subset were not clearly defined. The availability of a protective vaccine against C. burnetii has enabled studies of the immune response to postvaccine Coxiella challenge, which showed that the adaptive immune response is involved in successful resolution of postvaccination Coxiella infections. Indeed, studies using vaccination models have suggested that the predominant immune response to i.p. infection is T cell mediated (12). Immunized B-cell-deficient mice are capable of clearing i.p. delivered C. burnetii NMI, although the mice exhibit histopathological changes, suggesting that B cells may be important for controlling inflammatory damage during a secondary response, possibly through production of interleukin-10 (IL-10) (3).     

Regulators of Glucose Metabolism in CD4+ and CD8+ T Cells

Much like cancer cells, activated T cells undergo various metabolic changes that allow them to grow and proliferate rapidly. By adopting aerobic glycolysis upon activation, T cells effectively prioritize efficiency in biosynthesis over energy generation. There are distinct differences in the way CD4⁺ and CD8⁺ T cells process activation signals. CD8⁺ effector T cells are less dependent on Glut1 and oxygen levels compared to their CD4⁺ counterparts. Similarly the downstream signaling by TCR also differs in both effector T cell types. Recent studies have explored PI3K/Akt, mTORC, HIF1α, p70S6K and Bcl-6 signaling in depth providing definition of the crucial roles of these regulators in glucose metabolism. These new insights may allow improved therapeutic manipulation against inflammatory conditions that are associated with dysfunctional T-cell metabolism such as autoimmune disorders, metabolic syndrome, HIV, and cancers.     

Heterogenous Populations of Tissue-Resident CD8+ T Cells Are Generated in Response to Infection and Malignancy

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Concentrations of Soluble CD95 and CD8 Antigens in the Plasma and Levels of CD8+CD95+, CD8+CD38+, and CD4+CD95+ T Cells Are Markers for HIV-1 Infection and Clinical Status

Apoptosis mediated via the CD95 (FAS/APO-1) receptor is thought to play a role in the depletion of CD4+ T cells in HIV infection. In the present study expression of the CD95 antigen on lymphocyte subsets and the plasma level of soluble CD95 (sCD95) were determined in HIV-1-infected adults. The expression of CD95 was increased on CD8 cells in all groups of HIV+ individuals, while increased expression of CD95+ cells on CD4 cells was limited to individuals with CD4 counts of <200 mm³. The proportion of CD4+ that expressed CD95 was inversely correlated with the percentage of CD4+ PBL. The concentration of sCD95 was significantly higher in the plasma of HIV-infected individuals than in normal controls. The level of sCD95 in HIV-infected subjects showed no correlation with the percentage of PBL expressing CD95, indicating that the increased level of sCD95 did not reflect release from CD95+ PBL. The plasma sCD95 concentration was significantly correlated with the percentage of CD8+ cells and, particularly, with CD8+CD38– cells. A striking inverse correlation was found between the sCD95 plasma concentration and the proportion of CD4+CD95+ cells out of the total CD4+ population. There was no correlation between the serum level of sCD95 and that of soluble CD8 (sCD8), both of which were increased in the plasma of HIV+ individuals. Unlike the level of sCD95, the level of sCD8 in the plasma of HIV+ individuals. Unlike the level of sCD95, the level of sCD8 in the plasma of HIV+ individuals was correlated with the percentage of CD95+ and CD8+CD38+ cells. The present study indicates that plasma sCD95 may be one of the factors that regulate apoptotic death of lymphocytes in HIV infection.     

CD4+ CD25+ T Cells Prevent Arthritis Associated with Borrelia Vaccination and Infection

CD4⁺ CD25⁺ T cells are a population of regulatory T cells associated with control of arthritis in anti-interleukin-17 antibody-treated Borrelia-vaccinated and challenged gamma interferon-deficient mice. Here, we present direct evidence that adoptive transfer of enriched CD4⁺ CD25⁺ T cells from these mice can prevent the development of arthritis in Borrelia-vaccinated and challenged mice. These findings establish a major role for CD4⁺ CD25⁺ T cells in the prevention of arthritis in Borrelia-vaccinated and challenged animals.     

Prognostic Values of CD38+CD101+PD1+CD8+ T Cells in Pancreatic Cancer

Programmed death-1 (PD-1), a key immune checkpoint molecule, has been developed as an oncotherapy target for various carcinomas. However, treatment with anti-PD-1 elicited only a minimal effect in pancreatic ductal adenocarcinoma (PDAC). Subsequent studies revealed the existence of a subset of PD-1⁺ T cells coexpressing CD38 and CD101, representing a fixed dysfunctional subpopulation that are not able to be rescued by anti-PD-1 immunotherapy. However, whether this subpopulation of PD-1 expressing CD8⁺ T cells could be useful in predicting PDAC stage or prognosing survival is unknown. In this study, we used flow cytometry and immunofluorescence assay to analyze the expression of CD38 and CD101 in 183 clinical PDAC samples, including 84 of peripheral blood and 99 of surgical tissues. High coexpression of CD38/CD101 on peripheral PD-1⁺CD8⁺ T cells or tumor-infiltrating lymphocytes (TILs) was found to be most significantly correlated with Tumor/Node/Metastasis (T/N/M) classification and clinical stage, in contrast PD-1⁺CD8⁺ T cells could not correlate with T classification. CD38/CD101 co-repression on TILs also correlated with the poor survival in these PDAC patient samples. Our data suggest that CD38/CD101 might represent a more helpful biomarker than PD-1 alone for diagnosis and prognosis of PDAC.     

Generation and Regulation of CD8＋ Regulatory T Cells

Research into the suppressive activity of CD4＋FoxP3＋ T regulatory cells （Treg） has defined a sublineage of CD4＋ cells that contribute to self-tolerance and resistance to autoimmune disease. Much less attention has been given to the potential contribution of regulatory sublineages of CD8＋ cells. Analysis of a small fraction of CD8＋ cells that target autoreactive CD4＋ cells through recognition of the MHC class Ib molecule Qa-1 in mouse and HLA-E in human has revitalized interest in CD8＋ Treg. Here we summarize recent progress and future directions of research into the role of this CD8＋ sublineage in resistance to autoimmune disease. Cellular ＆ Molecular Immunology. 2008; 5（6）：401-406.     

CD8+ T Cells Specific for a Malaria Cytoplasmic Antigen Form Clusters around Infected Hepatocytes and Are Protective at the Liver Stage of Infection

Following Anopheles mosquito-mediated introduction into a human host, Plasmodium parasites infect hepatocytes and undergo intensive replication. Accumulating evidence indicates that CD8⁺ T cells induced by immunization with attenuated Plasmodium sporozoites can confer sterile immunity at the liver stage of infection; however, the mechanisms underlying this protection are not clearly understood. To address this, we generated recombinant Plasmodium berghei ANKA expressing a fusion protein of an ovalbumin epitope and green fluorescent protein in the cytoplasm of the parasite. We have shown that the ovalbumin epitope is presented by infected liver cells in a manner dependent on a transporter associated with antigen processing and becomes a target of specific CD8⁺ T cells from the T cell receptor transgenic mouse line OT-I, leading to protection at the liver stage of Plasmodium infection. We visualized the interaction between OT-I cells and infected hepatocytes by intravital imaging using two-photon microscopy. OT-I cells formed clusters around infected hepatocytes, leading to the elimination of the intrahepatic parasites and subsequent formation of large clusters of OT-I cells in the liver. Gamma interferon expressed in CD8⁺ T cells was dispensable for this protective response. Additionally, we found that polyclonal ovalbumin-specific memory CD8⁺ T cells induced by de novo immunization were able to confer sterile protection, although the threshold frequency of the protection was relatively high. These studies revealed a novel mechanism of specific CD8⁺ T cell-mediated protective immunity and demonstrated that proteins expressed in the cytoplasm of Plasmodium parasites can become targets of specific CD8⁺ T cells during liver-stage infection.     

Response of CD4+ and CD8+ T lymphocytes in the evolution of Leishmania (Viannia) shawi infection

Leishmania (Viannia) shawi was recently characterized, and there are no studies of immunopathological alterations induced by this parasite. BALB/c and C57BL/6 mice were infected in the footpad with L. (V.) shawi promastigotes. The lesions were monitored during 8?weeks post-infection (pi), and at each 2?weeks pi, immunohistochemistry of skin and lymph nodes has been performed to analyze the densities of CD4+ and CD8+ T lymphocytes as well as amastigote forms. In the skin, BALB/c mice presented higher amastigote densities than C57BL/6 mice; concerning lymphocytes, there are no significant differences between CD4+ T lymphocytes densities; however, C57BL/6 mice presented elevation in densities of CD8+ T cells latter in the infection. The elevation of amastigote densities in lymph nodes of BALB/c mice at 8?weeks pi could be a reflection of suppressed density of CD4+ T. On the other hand, elevated density of CD8+ T lymphocytes in lymph nodes of C57BL/6 seems to exert some degree of resistance compared to BALB/c mice. The present work indicates that CD8+ T lymphocyte can be a key component to generation of resistance in L. (V.) shawi infections.     

记忆性C D8+ T细胞免疫应答机制

免疫记忆是高等脊椎动物获得性免疫应答的显著特征。体液免疫应答与细胞免疫应答构成免疫记忆的两大重要分支。免疫记忆是指机体在对某一抗原产生特异性识别及应答的同时,记住该抗原,当再次遭遇同一抗原时,能发生快速和强烈的免疫应答。记忆性T细胞与感染免疫、肿瘤免疫、疫苗设计、自身免疫性疾病和移植排反应都有着密切的关系,深入研究记忆性T细胞的生成、维持、功能和调控机制不仅能指导新型疫苗的设计,有望更好的治疗疾病。     

Distinct Contributions of CD4+ and CD8+ T Cells to Pathogenesis of Trypanosoma brucei Infection in the Context of Gamma Interferon and Interleukin-10

Although gamma interferon (IFN-γ) and interleukin-10 (IL-10) have been shown to be critically involved in the pathogenesis of African trypanosomiasis, the contributions to this disease of CD4⁺ and CD8⁺ T cells, the major potential producers of the two cytokines, are incompletely understood. Here we show that, in contrast to previous findings, IFN-γ was produced by CD4⁺, but not CD8⁺, T cells in mice infected with Trypanosoma brucei. Without any impairment in the secretion of IFN-γ, infected CD8^−/− mice survived significantly longer than infected wild-type mice, suggesting that CD8⁺ T cells mediated mortality in an IFN-γ-independent manner. The increased survival of infected CD8^−/− mice was significantly reduced in the absence of IL-10 signaling. Interestingly, IL-10 was also secreted mainly by CD4⁺ T cells. Strikingly, depletion of CD4⁺ T cells abrogated the prolonged survival of infected CD8^−/− mice, demonstrating that CD4⁺ T cells mediated protection. Infected wild-type mice and CD8^−/− mice depleted of CD4⁺ T cells had equal survival times, suggesting that the protection mediated by CD4⁺ T cells was counteracted by the detrimental effects of CD8⁺ T cells in infected wild-type mice. Interestingly, CD4⁺ T cells also mediated the mortality of infected mice in the absence of IL-10 signaling, probably via excessive secretion of IFN-γ. Finally, CD4⁺, but not CD8⁺, T cells were critically involved in the synthesis of IgG antibodies during T. brucei infections. Collectively, these results highlight distinct roles of CD4⁺ and CD8⁺ T cells in the context of IFN-γ and IL-10 during T. brucei infections.     

肺炎支原体感染患儿外周血CD4+CD25+调节性T细胞的变化及其临床意义

探讨肺炎支原体(MP)感染患儿外周血CD4+ CD25+调节性T细胞(Treg)频率变化及其意义.选取32例肺炎支原体感染患儿,其中肺炎支原体肺炎18例,肺炎支原体肺炎合并肺外症状14例;26名健康儿童,分离其外周血单个核细胞,以CD4、CD25单克隆抗体标记细胞后,用流式细胞仪(FACS)检测Treg细胞频率.FAC...     

Transfer of CD8+ T Cells into SCID Mice and Activation of Memory Virus-Specific Cytotoxic T Cells

The requirements for the activation of naive and memory CD8⁺ cytotoxic T(Tc) cells into effector virus-specific Tc cells after transferring them into SCID mice were investigated. SCID mice reconstituted with splenocytes or purified CDS⁺ T cells from naive or influenza-immune syngeneic mice and immunized with influenza virus generated effector Tc cells specific for influenza virus-infected target cells in vitro. The kinetics of Ihe response varied between those two populations. The generation of effector Tc cells after transfer of memory CD8⁺ T cells indicates that there exists no absolute requirement for “help” in the activation of memory virus-immune Tc cells. However, under the conditions described here the in vitro immunogenic peptide NPP derived from influenza nucleoprotein is not sufficient to elicit a response in vivo.     

Donor CD8+ T Cells Prevent Toxoplasma gondii De-Encystation but Fail To Rescue the Exhausted Endogenous CD8+ T Cell Population

Functional exhaustion of CD8⁺ T cells due to increased expression of inhibitory molecule PD-1 (Programmed Death-1) causes reactivation of latent disease during later phases of chronic toxoplasmosis. Onset of disease recrudescence results in decreased parasite cyst burden concomitant with parasites undergoing stage conversion from a primarily encysted, quiescent bradyzoite to a fast-replicating, highly motile tachyzoite. Thus, reduced cyst burden is one of the early hallmarks of disease recrudescence. This was further validated by depleting gamma interferon (IFN-γ), a cytokine known to control latent toxoplasmosis, in chronically infected prerecrudescent mice. Since CD8⁺ T cells (an important source of IFN-γ) lose their functionality during the later phases of chronic toxoplasmosis, we next examined if adoptive transfer of functional CD8⁺ T cells from acutely infected donors to the chronically infected prerecrudescent hosts could impede parasite de-encystation and rescue exhausted CD8⁺ T cells. While the transfer of immune CD8⁺ T cells temporarily restricted the breakdown of cysts, the exhausted endogenous CD8⁺ T cell population was not rescued. Over time, the donor population got deleted, resulting in parasite de-encystation and host mortality. Considering that donor CD8⁺ T cells fail to become long-lived, one of the cardinal features of memory CD8⁺ T cells, it bears the implication that memory CD8 differentiation is impaired during chronic toxoplasmosis. Moreover, our data strongly suggest that while adoptive immunotherapy can prevent parasite de-encystation transiently, reduced antigen burden in the chronic phase by itself is insufficient for rescue of exhausted CD8⁺ T cells. The conclusions of this study have profound ramifications in designing immunotherapeutics against chronic toxoplasmosis.