Protective and Pathological Functions of CD8+ T Cells in Leishmania braziliensis Infection

Cutaneous leishmaniasis (CL) caused by Leishmania braziliensis is characterized by a strong Th1 response that leads to skin lesion development. In areas where L. braziliensis transmission is endemic, up to 15% of healthy subjects have tested positive for delayed-type hypersensitivity to soluble leishmania antigen (SLA) and are considered to have subclinical (SC) infection. SC subjects produce less gamma interferon (IFN-γ) and tumor necrosis factor alpha (TNF-α) than do CL patients, but they are able to control the infection. The aim of this study was to characterized the role of CD8⁺ T cells in SC infection and in CL. Peripheral blood mononuclear cells (PBMC) were stimulated with SLA to determine the frequencies of CD4⁺ IFN-γ⁺ and CD8⁺ IFN-γ⁺ T cells. Monocytes from PBMC were infected with L. braziliensis and cocultured with CD8⁺ T cells, and the frequencies of infected monocytes and levels of cytotoxicity markers, target cell apoptosis, and granzyme B were determined. The frequency of CD8⁺ IFN-γ⁺ cells after SLA stimulation was higher for SC individuals than for CL patients. The frequency of infected monocytes in SC cells was lower than that in CL cells. CL CD8⁺ T cells induced more apoptosis of infected monocytes than did SC CD8⁺ T cells. Granzyme B production in CD8⁺ T cells was higher in CL than in SC cells. While the use of a granzyme B inhibitor decreased the number of apoptotic cells in the CL group, the use of z-VAD-FMK had no effect on the frequency of these cells. These results suggest that CL CD8⁺ T cells are more cytotoxic and may be involved in pathology.     

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.     

CD38+CD8+ and CD38+CD4+ T Cells and IFN Gamma (+874) Polymorphism Are Associated with a Poor Virological Outcome

The main objective of the work was to evaluate the use of CD38 on T lymphocytes, IFNγ (+874 A/T), and IL-10 (?1082 A/G) polymorphisms in HIV-infected patients under antiretroviral (ARV) therapy. Sixty-one patients were selected at the outpatient clinic for HIV infection at the Hospital São José de Doenças Infecciosas, Fortaleza, Ceará, Brazil. The patients were classified into two groups, according to viral load after one year of ARV therapy. In the aviremic group (group I), a reduction of 35.5% of CD38+CD4+ T cells was observed (p = 0.02) and 49.3% of CD38+CD8+ T cells (p = 0.001). In the viremic group (group II), a reduction of 37.2% of CD38+CD4+ T cells (p = 0.067), and 21.4% of CD38+CD8+ T cells (p = 0.60) occurred. No association was found between IL-10 (?1082) polymorphism and the type of response to ARV therapy. Regarding the gene polymorphism on IFNγ (+874 T/A), 73.34% of group I and 33.3% of group II presented the AA genotype. The relative risk of the individuals carrying AA genotype or the A allele and not being able to suppress the viral load level after one year of ARV therapy was 3.44 (1.25–9.45; p = 0.014) or 2.35 (1.05–5.26; p = 0.027), respectively. Our data suggested that an augmented frequency of activated CD38+CD8+ T cells as well as the presence of the A allele of IFNγ polymorphism could contribute to a reduced virological suppression in patients under antiretroviral therapy.     

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).     

Towards Developing a Malaria Vaccine Based on CD4 T Cell Mediated Immunity in Blood Stage of Malaria Infection

Twenty-one years after malaria antigens were first cloned avaccine still appears to be a long way off. There havebeen periods of great excitement and in model systemssubunit vaccine homologues can induce robust protection.However, significant challenges e…     

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.     

Cytotoxicity and Secretion of Gamma Interferon Are Carried Out by Distinct CD8 T Cells during Mycobacterium tuberculosis Infection

The host immune response is generally sufficient to contain Mycobacterium tuberculosis infection. It does not, however, efficiently prevent subsequent infection with M. tuberculosis or provide sterilizing immunity. While the understanding of the immune response generated against this pathogen is incomplete, improvements have been achieved due to advances in immunological tools. In this study, we analyzed the multifunctional nature of primary and memory CD8 T-cell responses generated during murine M. tuberculosis infection. We generated a recombinant M. tuberculosis strain expressing ovalbumin (OVA) epitopes in order to expand the peptides for the detection of CD8 T cells during M. tuberculosis infection and enable us to use OVA-specific reagents. Our results indicate that the majority of M. tuberculosis-specific CD8 T cells are limited to either cytotoxicity or the secretion of gamma interferon (IFN-γ), with cytotoxicity being far more prevalent than IFN-γ secretion. Memory CD8 T cells responded earlier and reached higher levels in the lungs than naïve CD8 T cells, as was expected. They were, however, less cytotoxic and secreted less IFN-γ than newly primed CD8 T cells, suggesting that one factor contributing to bacterial persistence and lack of sterilizing immunity may be the low quality of memory cells that are generated.Mycobacterium tuberculosis, the pathogen causing tuberculosis, is an escalating global health threat that is spread between people by aerosolized droplets. While a subset of people develop primary disease and are infectious, most people contain the infection through a successful immune response. Typing of M. tuberculosis strains has shown that people can be infected simultaneously or sequentially with different strains of M. tuberculosis (29, 37). Thus, immune responses that are sufficient to contain an initial infection may be unable to prevent the establishment of subsequent M. tuberculosis infections. In addition, persons treated for tuberculosis with antimycobacterial drugs can be reinfected and develop disease (36). This is also true in animal models (8, 16, 32). This suggests that memory responses generated during previous mycobacterial infections are not generally capable of protecting against new infections or disease.It is currently unknown which, if any, immune functions can protect against establishment of infection. In terms of T-cell responses, gamma interferon (IFN-γ) and tumor necrosis factor can activate infected macrophages to induce antimicrobial activity, while cytolysis of infected cells can kill the bacterium or release it to be taken up by healthy cells that are better able to contain it (12, 21). Most studies of the role of CD8 T cells during M. tuberculosis infection have focused on either IFN-γ secretion or cytotoxicity. A few studies have examined both functions but not on a single-cell basis (6, 17, 19). These studies indicated that CD8 T-cell-mediated IFN-γ secretion and cytotoxicity peak in the lungs at 4 weeks postinfection. IFN-γ secretion subsequently decreases, while the results differ as to whether cytotoxicity decreases. This difference may be due to variation between mouse strains and epitopes or the techniques used to assess cytotoxicity.In the current study, we demonstrate that most M. tuberculosis-specific CD8 T cells generated during primary infection were limited to either secretion of IFN-γ or cytotoxic function. There was a higher fraction of CD8 T cells with cytotoxic potential compared to those that produced IFN-γ. The CD8 T-cell memory response was similarly exclusive in function. Despite increased degranulation, cells responding during secondary infection were less cytotoxic than cells responding during primary infection. Induction of superior quality CD8 T cells may provide a benefit during M. tuberculosis infection, but a more detailed understanding of the complex T-cell response to M. tuberculosis is necessary for the development of future preventive and therapeutic strategies.     

Memory CD8+ T Cells Are Sufficient To Alleviate Impaired Host Resistance to Influenza A Virus Infection Caused by Neonatal Oxygen Supplementation

Supplemental oxygen administered to preterm infants is an important clinical intervention, but it is associated with life-long changes in lung development and increased sensitivity to respiratory viral infections. The precise immunological changes caused by neonatal oxygen treatment remain poorly understood. We previously reported that adult mice exposed to supplemental oxygen as neonates display persistent pulmonary inflammation and enhanced mortality after a sublethal influenza A virus infection. These changes suggest that neonatal hyperoxia impairs the cytotoxic CD8(+) T cell response required to clear the virus. In this study, we show that although host resistance to several different strains of influenza A virus is reduced by neonatal hyperoxia, this treatment does not impair viral clearance, nor does it alter the magnitude of the virus-specific CD8(+) T cell response to primary infection. Moreover, memory T cells are sufficient to ameliorate the increased morbidity and mortality and alleviate the excessive lung damage observed in mice exposed to high oxygen levels as neonates, and we attribute this sufficiency principally to virus-specific memory CD8(+) T cells. Thus, we show that neonatal hyperoxia reduces host resistance to influenza virus infection without diminishing the function of cytotoxic T lymphocytes or the generation of virus-specific memory T cells and that CD8(+) memory T cells are sufficient to provide protection from negative consequences of this important life-saving intervention. Our findings suggest that vaccines that generate robust T cell memory may be efficacious at reducing the increased sensitivity to respiratory viral infections in people born prematurely.     

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.     

调节性T细胞修饰前炎症应答对小鼠脑型疟疾发生的影响

为探讨调节性T细胞（Tregs）对伯氏疟原虫感染所致鼠脑型疟发生和感染结局的影响机制,用伯氏疟原虫ANKA株分别感染对照组和抗CD25单克隆抗体注射组C57BL／6小鼠,计数红细胞感染率;感染前和感染后3、5、8天制备脾细胞悬液,流式细胞术检测脾Tregs百分含量;ELISA和Griess方法检测脾细胞培养上清IFN-γ、IL-10和NO水平。结果表明大多数C57BL／6鼠于感染后8—11天死于脑疟,抗CD25单克隆抗体注射组小鼠感染后3～4周死于贫血和过度原虫血症。对照组小鼠脾细胞培养上清IFN-γ、NO、IL—10水平于感染后开始升高,感染后5天达到峰值,感染后8天与感染后5天相比,IFN-γ、NO轻微下降,IL-10显著下降。感染后3、5天,实验组IFN-γ、NO水平显著高于对照组,IL—10水平显著低于对照组。感染后8天,实验组和对照组IFN-γ、NO、IL-10水平得到逆转。这表明Tregs通过修饰前炎症应答影响伯氏疟原虫感染鼠脑型疟发生和感染结局。     

IRGM3 Contributes to Immunopathology and Is Required for Differentiation of Antigen-Specific Effector CD8+ T Cells in Experimental Cerebral Malaria

Gamma interferon (IFN-γ) drives antiparasite responses and immunopathology during infection with Plasmodium species. Immunity-related GTPases (IRGs) are a class of IFN-γ-dependent proteins that are essential for cell autonomous immunity to numerous intracellular pathogens. However, it is currently unknown whether IRGs modulate responses during malaria. We have used the Plasmodium berghei ANKA (PbA) model in which mice develop experimental cerebral malaria (ECM) to study the roles of IRGM1 and IRGM3 in immunopathology. Induction of mRNA for Irgm1 and Irgm3 was found in the brains and spleens of infected mice at times of peak IFN-γ production. Irgm3^−/− but not Irgm1^−/− mice were completely protected from the development of ECM, and this protection was associated with the decreased induction of inflammatory cytokines, as well as decreased recruitment and activation of CD8⁺ T cells within the brain. Although antigen-specific proliferation of transferred CD8⁺ T cells was not diminished compared to that of wild-type recipients following PbA infection, T cells transferred into Irgm3^−/− recipients showed a striking impairment of effector differentiation. Decreased induction of several inflammatory cytokines and chemokines (interleukin-6, CCL2, CCL3, and CCL4), as well as enhanced mRNA expression of type-I IFNs, was found in the spleens of Irgm3^−/− mice at day 4 postinfection. Together, these data suggest that protection from ECM pathology in Irgm3^−/− mice occurs due to impaired generation of CD8⁺ effector function. This defect is nonintrinsic to CD8⁺ T cells. Instead, diminished T cell responses most likely result from defective initiation of inflammatory responses in myeloid cells.     

CD38brightCD8+ T Cells Associated with the Development of Acute GVHD Are Activated,Proliferating, and Cytotoxic Trafficking Cells

We have previously reported that a peripheral blood absolute CD38^brightCD8⁺ effector memory T cell (TEM) population expansion of >35 cells/µL predicts the development of acute graft-versus-host disease (GVHD). We hypothesized that these T cells are activated, proliferating, and cytotoxic trafficking cells that are not a response to viral reactivation and may be involved in acute GVHD. We characterized peripheral blood T cell populations at the time of maximum CD38^brightCD8⁺ TEM expansion in patients from our originally reported pediatric allogeneic hematopoietic cell transplantation recipient cohort. Samples were incubated with fluorochrome-conjugated antibodies directed against CD3, CD8, CD38, HLA-DR (T cell activation), Ki-67 (T cell proliferation), granzyme B (marker of cytotoxic T cells), CLA (skin trafficking), CCR5 (visceral trafficking), and CXCR6 (liver trafficking). We also incubated samples with Epstein-Barr virus (EBV) and cytomegalovirus (CMV) peptide pools and measured IFN-γ production by flow cytometry and performed EBV and CMV tetramer staining. Higher median proportions of cell expression of HLA-DR, Ki-67, granzyme B, CLA, CCR5, and CXCR6 were observed for CD38^brightCD8⁺ T cells compared with CD38^nonbrightCD8⁺ T cells in patients with acute GVHD (P < .05) but not in patients without acute GVHD (P not significant). No IFN-γ production was observed after incubation with CMV and EBV peptide pools. EBV-specific tetramer populations of 6.85% and 3.17% were detected in 2 patients with acute GVHD, whereas a CMV-specific tetramer population of 3.77% was detected in 1 patient with acute GVHD. No EBV- or CMV-specific tetramer populations were detected in any patient without acute GVHD. We conclude that CD38^brightCD8⁺ T cells associated with the development of acute GVHD are activated, proliferating, and cytotoxic trafficking cells that do not appear to respond to CMV or EBV reactivation. Further studies are needed to determine whether these cells are directly involved in acute GVHD pathogenesis.     

CD4+ T Cells and Antibody Are Required for Optimal Major Outer Membrane Protein Vaccine-Induced Immunity to Chlamydia muridarum Genital Infection

Despite effective antimicrobial chemotherapy, control of Chlamydia trachomatis urogenital infection will likely require a vaccine. We have assessed the protective effect of an outer membrane protein-based vaccine by using a murine model of chlamydial genital infection. Female mice were first vaccinated with Chlamydia muridarum major outer membrane protein (MOMP) plus the adjuvants CpG-1826 and Montanide ISA 720; then they were challenged with C. muridarum. Vaccinated mice shed 2 log₁₀ to 3 log₁₀ fewer inclusion-forming units (IFU) than ovalbumin-vaccinated or naïve animals, resolved infection sooner, and had a lower incidence of hydrosalpinx. To determine the relative contribution of T cells to vaccine-induced protection, mice were vaccinated, depleted of CD4⁺ or CD8⁺ T cells, and then challenged vaginally with C. muridarum. Depletion of CD4⁺ T cells, but not depletion of CD8⁺ T cells, diminished vaccine-induced protection, with CD4-depleted mice shedding 2 log₁₀ to 4 log₁₀ more IFU than CD8-depleted or nondepleted mice. The contribution of antibodies to vaccine-induced protection was demonstrated by the absence of protective immunity in vaccinated B-cell-deficient mice and by a 2 log₁₀ to 3 log₁₀ decrease in bacterial shedding by mice passively administered an anti-MOMP serum. Thus, optimal protective immunity in this model of vaccine-induced protection depends on contributions from both CD4⁺ T cells and antibody.New cases of sexually transmitted diseases number more than 340 million worldwide annually and pose a formidable health risk to infected individuals (67-69). It is estimated that Chlamydia trachomatis, the causative agent of chlamydia, is responsible for more than 92 million of these cases. In the United States, where C. trachomatis infections are the infections most commonly reported to the Centers for Disease Control and Prevention, there are more than 4 million new cases each year (14, 67). As a bacterial agent of infection, C. trachomatis can be eradicated efficiently with appropriate antibiotic treatment, but more than 50% of infected individuals are asymptomatic and therefore lack the impetus to seek treatment (14). When left untreated, infection in women can lead to pelvic inflammatory disease, ectopic pregnancy, and tubal factor infertility and can cause severe and sometimes irreparable damage to the reproductive organs (14, 67). To combat the high rate of infection and disease, the development of an efficacious vaccine is critical.Trachoma vaccine trials using whole organisms in the 1950s and 1960s had mixed results, with some studies inducing only partial, serovar-specific, short-lived immunity (4). In one study, a subset of vaccine trial participants experienced an increased incidence of disease and exacerbated pathology relative to that of their unvaccinated counterparts upon reexposure to chlamydiae, which led many researchers to abandon the use of whole organisms in immunizations (7, 8). Since then, no other human vaccine trials targeting ocular or urogenital C. trachomatis infections have been published. Instead, researchers have focused their efforts on animal models of ocular and genital infection.To this end, the murine model of chlamydial genital infection, which closely mimics acute genital infection in women, has been employed extensively for the study of the immunological parameters of infection and for vaccine development. Mice infected with C. muridarum naturally resolve infection in approximately 4 weeks and develop long-lived adaptive immunity that markedly protects against reinfection (3, 37). Infection elicits Chlamydia-specific CD4⁺ T cells, CD8⁺ T cells, and antibody, but only CD4⁺ T cells are necessary for resolution of the primary infection (42). In contrast, immunity to reinfection is dominated by both protective CD4⁺ T cells and antibody (38). Clearance and immunity are highly dependent on a Th1-type response, specifically gamma interferon (IFN-γ)-secreting CD4 cells (9). On the other hand, Th2 responses are associated with scarring and immunopathology (62). For example, antibody responses dominated by IgG1 are not protective and may be associated with an increase in pathology, whereas anti-chlamydial antibodies of the IgG2a and IgG2b isotypes are associated with a protective response (51).Using knowledge of the protective response gleaned from the murine model of infection-induced immunity, investigators have made modest strides toward the development of an efficacious vaccine. Studies utilizing whole elementary body (EB) immunization have induced significant protection, though most of these studies have limited real-world application. One notable example that induced almost sterilizing immunity involved the passive transfer of dendritic cells pulsed ex vivo with nonviable chlamydiae (65). Subunit antigen vaccines represent the bulk of vaccine studies, and vaccines based on combinations of a number of chlamydial antigens, adjuvants, and delivery systems have had various degrees of success in preventing infection (8, 22, 62). Chlamydial antigens, including secreted proteins, such as chlamydial protease-like activity factor (CPAF) (16, 33, 43-46), and membrane associated proteins, such as PorB (26, 30) and IncA (33), have also been used in subunit vaccines; however, the vast majority of studies have focused on the major outer membrane protein (MOMP), an immunodominant antigen in both human and animal studies (22, 62). Novel delivery systems, including Vibrio cholerae ghosts and cationic liposomes, have been introduced into chlamydial vaccine research, and while initial studies have shown incomplete protection, these systems may have the potential to elicit protective responses against chlamydial genital infection when used in conjunction with appropriate antigens (2, 19, 20, 23).Despite substantial effort, no vaccine licensed for human use is currently available. Recently, a MOMP-based vaccine utilizing the adjuvants CpG-1826 and Montanide ISA 720, which together drive a strong Th1-type response, has been shown to confer considerable protection when mice are challenged directly in the upper genital tract with C. muridarum (51). In our current study, we sought to determine if this vaccine protected against vaginal challenge (the natural route of infection) and to evaluate the contributions of T cells and antibody to the vaccine-induced protective response. We found that the MOMP vaccine conferred significant protection against vaginal challenge and protected against infection-induced pathology (hydrosalpinx). Furthermore, optimal protection was dependent on both CD4⁺ T cells and antibody.     

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.     

Damage to the Blood-Brain Barrier during Experimental Cerebral Malaria Results from Synergistic Effects of CD8+ T Cells with Different Specificities

CD8⁺ T cells play a pathogenic role in the development of murine experimental cerebral malaria (ECM) induced by Plasmodium berghei ANKA (PbA) infection in C57BL/6 mice. Only a limited number of CD8⁺ epitopes have been described. Here, we report the identification of a new epitope from the bergheilysin protein recognized by PbA-specific CD8⁺ T cells. Induction and functionality of these specific CD8⁺ T cells were investigated in parallel with previously reported epitopes, using new tools such as tetramers and reporter cell lines that were developed for this study. We demonstrate that CD8⁺ T cells of diverse specificities induced during PbA infection share many characteristics. They express cytolytic markers (gamma interferon [IFN-γ], granzyme B) and chemokine receptors (CXCR3, CCR5) and damage the blood-brain barrier in vivo. Our earlier finding that brain microvessels in mice infected with PbA, but not with non-ECM-causing strains, cross-presented a shared epitope was generalizable to these additional epitopes. Suppressing the induction of specific CD8⁺ T cells through tolerization with a high-dose peptide injection was unable to confer protection against ECM, suggesting that CD8⁺ T cells of other specificities participate in this process. The tools that we developed can be used to further investigate the heterogeneity of CD8⁺ T cell responses that are involved in ECM.