Echinococcus multilocularis proliferation in mice and respective parasite 14-3-3 gene expression is mainly controlled by an alphabeta CD4 T-cell-mediated immune response

The role of specific B lymphocytes and T-cell populations in the control of experimental Echinococus multilocularis infection was studied in micro MT, nude, T-cell receptor (TCR)-beta(-/-), major histocompatibility complex (MHC)-I(-/-) and MHC-II(-/-) mice. At 2 months postinfection, the parasite mass was more than 10 times higher in nude, TCR-beta(-/-) and MHC-II(-/-) mice than in infected C57BL/6 wild-type (WT) mice, and these T-cell-deficient mice started to die of the high parasite load at this time-point. In contrast, MHC-I(-/-) and micro MT mice exhibited parasite growth rates similar to those found in WT controls. These findings clearly point to the major role that CD4(+) alphabeta(+) T cells play in limiting the E. multilocularis proliferation, while CD8(+) T and B cells appeared to play a minor role in the control of parasite growth. In the absence of T cells, especially CD4(+) or alphabeta(+) T cells, the cellular immune response to infection was impaired, as documented by the lack of hepatic granuloma formation around the parasite and by a decreased splenocyte responsiveness to concanavalin A (Con A) and parasite antigen stimulation. Surprisingly, in T-cell-deficient mice, the ex vivo expression of interferon-gamma (IFN-gamma) and other inflammatory cytokines (except for interleukin-6) were increased in association with a high parasite load. Thus, the relative protection mediated by CD4(+) alphabeta(+) T cells against E. multilocularis infection seemed not be IFN-gamma dependent, but rather to rely on the effector's function of CD4(+) alphabeta(+) T cells. The local restriction of parasite germinal cell proliferation was reflected by a regulatory effect on the expression of 14-3-3 protein within the parasite tissue in T-cell-deficient mice. These results provide a strong indication that the CD4(+) alphabeta(+) T-cell-mediated immune response contributes to the control of the parasite growth and to the regulation of production of the parasite 14-3-3 protein in metacestode tissues.     

A GRA1 DNA vaccine primes cytolytic CD8(+) T cells to control acute Toxoplasma gondii infection

Protective immunity against Toxoplasma gondii is known to be mediated mainly by T lymphocytes and gamma interferon (IFN-gamma). The contribution of CD4(+) and CD8(+) T-lymphocyte subsets to protective immune responses against T. gondii infection, triggered by a GRA1 (p24) DNA vaccine, was assessed in this study. In vitro T-cell depletion experiments indicated that both CD4(+) and CD8(+) T-cell subsets produced IFN-gamma upon restimulation with a T. gondii lysate. In addition, the GRA1 DNA vaccine elicited CD8(+) T cells that were shown to have cytolytic activity against parasite-infected target cells and a GRA1-transfected cell line. C3H mice immunized with the GRA1 DNA vaccine showed 75 to 100% protection, while 0 to 25% of the mice immunized with the empty control vector survived challenge with T. gondii cysts. In vivo T-cell depletion experiments indicated that CD8(+) T cells were essential for the survival of GRA1-vaccinated C3H mice during the acute phase of T. gondii infection, while depletion of CD4(+) T cells led to an increase in brain cyst burden during the chronic phase of infection.     

Different roles are played by alpha beta and gamma delta T cells in acquired immunity to Chlamydia trachomatis pulmonary infection.

Using gene knockout and wild-type C57BL/6 mice, we examined the role of alpha beta and gamma delta T cells in the resolution of Chlamydia trachomatis mouse pneumonitis (MoPn) biovar pulmonary infection. The results show that alpha beta T-cell-deficient (alpha-/-) mice, when compared with wild-type control mice, have dramatically increased mortality rate and greater in vivo growth of MoPn. The alpha beta T-cell-deficient mice were as susceptible to MoPn infection as T- and B-lymphocyte-deficient (RAG-1-/-) mice. Moreover, both alpha beta T-cell-deficient and RAG-1 mutant mice failed to mount delayed-type hypersensitivity (DTH) responses to organism-specific challenge and showed undetectable interferon-gamma (IFN-gamma) production by spleen cells upon in vitro organism-specific restimulation. In contrast, gamma delta T-cell-deficient mice exhibited intact DTH responses and their mortality rate and in vivo chlamydial growth were comparable to those in wild-type controls. More interestingly, gamma delta T-cell-deficient mice showed significantly higher levels of IFN-gamma production than did wild-type mice. The data indicate that the alpha beta T cell is the major T-cell population for acquired immunity to chlamydial infection and that gamma delta T cells may play an ancillary role in regulating the magnitude of alpha beta T-cell responses.     

CD8(+) T cells participate in the memory immune response to Mycobacterium tuberculosis

The contribution of CD8(+) T cells to the control of tuberculosis has been studied primarily during acute infection in mouse models. Memory or recall responses in tuberculosis are less well characterized, particularly with respect to the CD8 T-cell subset. In fact, there are published reports that CD8(+) T cells do not participate in the memory immune response to Mycobacterium tuberculosis. We examined the CD8(+) T-cell memory and local recall response to M. tuberculosis. To establish a memory immunity model, C57BL/6 mice were infected with M. tuberculosis, followed by treatment with anti-mycobacterial drugs and prolonged rest. The lungs of memory immune mice contained CD4(+) and CD8(+) T cells with the cell surface phenotype characteristic of memory cells (CD69(low) CD25(low) CD44(high)). At 1 week postchallenge with M. tuberculosis via aerosol, > or =30% of both CD4(+) and CD8(+) T cells in the lungs of immune mice expressed the activation marker CD69 and could be restimulated to produce gamma interferon (IFN-gamma). In contrast, <6% of T cells in the lungs of naive challenged mice were CD69(+) at 1 week postchallenge, and IFN-gamma production was not observed at this time point. CD8(+) T cells from the lungs of both naive and memory mice after challenge were cytotoxic toward M. tuberculosis-infected macrophages. Our data indicate that memory and recall immunity to M. tuberculosis is comprised of both CD4(+) and CD8(+) T lymphocytes and that there is a rapid response of both subsets in the lungs following challenge.     

Ineffective cellular immune response associated with T-cell apoptosis in susceptible Mycobacterium bovis BCG-infected mice

It has previously been reported that inhibition of delayed-type hypersensitivity-mediating functions of T cells during mycobacterial infection in mice is haplotype dependent. In the present study, we show that Mycobacterium bovis BCG infection induced, in susceptible C57BL/6 and BALB/c mice but not in resistant C3H/HeJ and DBA/2 mice, an important splenomegaly. An in vitro defect in T-cell proliferation in response to T-cell receptor (TCR) stimulation with mitogens or anti-CD3 antibodies was associated with enhanced levels of CD4(+) and CD8(+) T-cell apoptosis in susceptible but not in resistant mice 2 weeks after infection. Further investigations of C57BL/6 and C3H/HeJ mice revealed that in vivo splenomegaly was associated with destruction of the lymphoid tissue architecture, liver cellular infiltrates, and increased numbers of apoptotic cells in both spleen and liver tissue sections. Infection of C57BL/6 mice but not of C3H/HeJ mice induced massive production of tumor necrosis factor alpha (TNF-alpha) in serum, as well as an increase in Fas and Fas ligand (FasL) expression in T cells. In vitro addition of neutralizing anti-TNF-alpha antibodies led to a significant reduction in CD3-induced T-cell apoptosis of both CD4(+) and CD8(+) T cells of C57BL/6 mice, while the blockade of Fas-FasL interactions reduced apoptosis only in CD4(+) but not in CD8(+) T cells. Together, these results suggest that TNF-alpha and Fas-FasL interactions play a role in the activation-induced cell death (AICD) process associated with a defect in T-cell proliferation of the susceptible C57BL/6 mice. T-cell death by apoptosis may represent one of the important components of the ineffective immune response against mycobacterium-induced immunopathology in susceptible hosts.     

T-cell-mediated immune response in murine malaria: differential effects of antigen-specific Lyt T-cell subsets in recovery from Plasmodium yoelii infection in normal and T-cell-deficient mice.

For analysis of the role of immune T cells in protective immunity against murine malaria, Plasmodium yoelii-immune Lyt T-cell subsets were functionally characterized in vitro and in vivo. Selected Lyt2- and Lyt2+ T cells from P. yoelii-immune C57BL/10 mice differed in their capability to proliferate in response to P. yoelii antigen in vitro. Only the Lyt2- T-cell population produced T-cell growth factor upon restimulation, and none of the selected T-cell subsets produced detectable amounts of macrophage activating factor. Lyt2- but not Lyt2+ lymphocytes were capable of transferring protection to normal C57BL/10 mice. When transferred into T-cell-deficient C57BL/6-nu/nu mice, adoptive resistance to P. yoelii by Lyt2- lymphocytes was only demonstrable after prior reconstitution of recipients with normal T cells. These results suggest an interaction between P. yoelii-immune Lyt2- T cells and normal T lymphocytes via T-cell growth factor in the development of protective immunity to malaria.     

Identification of murine H2-Dd- and H2-Ab-restricted T-cell epitopes on a novel protective antigen, MPT51, of Mycobacterium tuberculosis

Both CD4(+) type 1 helper T (Th1) cells and CD8(+) cytotoxic T lymphocytes (CTL) play pivotal roles in protection against Mycobacterium tuberculosis infection. Here, we identified Th1 and CTL epitopes on a novel protective antigen, MPT51, in BALB/c and C57BL/6 mice. Mice were immunized with plasmid DNA encoding MPT51 by using a gene gun, and gamma interferon (IFN-gamma) production from the immune spleen cells was analyzed in response to a synthetic overlapping peptide library covering the mature MPT51 sequence. In BALB/c mice, only one peptide, p21-40, appeared to stimulate the immune splenocytes to produce IFN-gamma. Flow cytometric analysis with intracellular IFN-gamma and the T-cell phenotype revealed that the p21-40 peptide contains an immunodominant CD8(+) T-cell epitope. Further analysis with a computer-assisted algorithm permitted identification of a T-cell epitope, p24-32. In addition, a major histocompatibility complex class I stabilization assay with TAP2-deficient RMA-S cells transfected with K(d), D(d), or L(d) indicated that the epitope is presented by D(d). Finally, we proved that the p24-32/D(d) complex is recognized by IFN-gamma-producing CTL. In C57BL/6 mice, we observed H2-A(b)-restricted dominant and subdominant Th1 epitopes by using T-cell subset depletion analysis and three-color flow cytometry. The data obtained are useful for analyzing the role of MPT51-specific T cells in protective immunity and for designing a vaccine against M. tuberculosis infection.     

Relative importance of CD4+ and CD8+ T cells in the resolution of Chlamydophila abortus primary infection in mice

The role of the specific cellular immune response is well established in Chlamydiaceae infections, but the importance of each T-cell subset seems to be species-dependent. This study was designed to clarify the role of T-cell subsets in the response to Chlamydophila abortus primary infection. C57BL/6 mice were depleted of CD4+ or CD8+, or both, by monoclonal antibody injections and subsequently infected with C. abortus. Mice were killed at intervals and samples were collected for bacteriological and histopathological analysis. Also carried out were spleen cell culture, cytokine quantification, immunolabelling for C. abortus antigen, and a TUNEL assay for apoptosis. CD8+ T cell-depleted mice all died within 12 days of C. abortus infection, while no mortality was observed in the other groups; surprisingly, CD4+ T cell-depleted mice showed lower morbidity (expressed as weight loss) than did a non-depleted (control) group. CD8+ T cell-depleted mice also differed from the other groups in showing a significantly higher chlamydial burden in the liver. CD8+ T cell-depleted mice also had a higher number of apoptotic cells in hepatic inflammatory foci and showed exacerbated IFN-gamma production by spleen cells after specific stimulation. Simultaneous depletion of both T-cell subpopulations led to a chronic infection, but not to early mortality. It is concluded that CD8+ T cells may play a role in the regulatory control of the CD4+ T-cell response and may have a direct cytotoxic or IFN-gamma-mediated effect on infected cells.     

Interleukin-23 (IL-23)-IL-17 cytokine axis in murine Pneumocystis carinii infection

Host defense mechanisms against Pneumocystis carinii are not fully understood. Previous work in the murine model has shown that host defense against infection is critically dependent upon host CD4(+) T cells. The recently described Th17 immune response is predominantly a function of effector CD4(+) T cells stimulated by interleukin-23 (IL-23), but whether these cells are required for defense against P. carinii infection is unknown. We tested the hypothesis that P. carinii stimulates the early release of IL-23, leading to increases in IL-17 production and lung effector CD4(+) T-cell population that mediate clearance of infection. In vitro, stimulation of alveolar macrophages with P. carinii induced IL-23, and IL-23p19 mRNA was expressed in lungs of mice infected with this pathogen. To address the role of IL-23 in resistance to P. carinii, IL-23p19-/- and wild-type control C57BL/6 mice were infected and their fungal burdens and cytokine/chemokine responses were compared. IL-23p19-/- mice displayed transient but impaired clearance of infection, which was most apparent 2 weeks after inoculation. In confirmatory studies, the administration of either anti-IL-23p19 or anti-IL-17 neutralizing antibody to wild-type mice infected with P. carinii also caused increases in fungal burdens. IL-17 and the lymphocyte chemokines IP-10, MIG, MIP-1alpha, MIP-1beta, and RANTES were decreased in the lungs of infected IL-23p19-/- mice in comparison to their levels in the lungs of wild-type mice. In IL-23p19-/- mice infected with P. carinii, there were fewer effector CD4(+) T cells in the lung tissue. Collectively, these studies indicate that the IL-23-IL-17 axis participates in host defense against P. carinii.     

Role of T cells in resistance to Theiler's virus infection.

Intracerebral infection of C57BL/10SNJ mice with Theiler's virus results in acute encephalitis with subsequent virus clearance and absence of spinal cord demyelination. In contrast, infection of SJL/J mice results in acute encephalitis, virus persistence, and immune-mediated demyelination. These experiments examined the role of T-cell subsets in the in vivo immune response to Theiler's virus in resistant C57BL/10SNJ mice. Depletion of T-cell subsets with monoclonal antibodies (mAbs) directed at CD3 (pan-T-cell marker), CD4+ (class II-restricted) or CD8+ (class I-restricted) T cells resulted in increased frequency of paralysis and death as a result of acute encephalitis. Neuropathologic studies 10 days after infection demonstrated prominent necrosis, primarily in the pyramidal layer of hippocampus and in the thalamus of mice depleted of T-cell subsets. In immunosuppressed and infected C57BL/10SNJ mice, analysis of spinal cord sections 35 days after infection demonstrated small demyelinated lesions relatively devoid of inflammatory cells even though virus antigen could be detected by immunocytochemistry. Both CD4+ and CD8+ T cells are important in the resistance to infection with Theiler's virus in C57BL/10SNJ mice. However, subsequent spinal cord demyelination, to the extent observed in susceptible mice, depends on the presence of virus antigen persistence and a competent cellular immune response.     

Quantitative, not qualitative, differences in CD8(+) T cell responses to Theiler's murine encephalomyelitis virus between resistant C57BL/6 and susceptible SJL/J mice

Theiler's murine encephalomyelitis virus (TMEV) infection of the CNS induces an immune-mediated demyelinating disease in susceptible mouse strains and serves as a relevant infection model for human multiple sclerosis. However, it is not yet clear what immunological parameters determine the susceptibility of SJL/J mice compared to resistant mice. We have here compared the TMEV-specific CD8(+) T cell responses in highly susceptible SJL/J mice with those of highly resistant C57BL/6 mice. Our results clearly indicate that the levels of initial responses of infiltrating CD8(+) T cells to viral capsid proteins are higher in resistant C57BL/6 mice compared to susceptible SJL/J mice. However, the level of virus-specific CD8(+) T cells was much more rapidly reduced in resistant C57BL/6, resulting in a higher CD8(+) T cell level in SJL/J mice later in viral infection. The activation states, cytokine production, as well as the cytolytic function of the CD8(+) T cells were similar to each other in these mice. These results suggest that an initial induction of a vigorous CD8(+) T cell response to TMEV is critically important for the resistance to virally induced demyelinating disease.     

Gamma interferon-induced T-cell loss in virulent Mycobacterium avium infection

Infection by virulent Mycobacterium avium caused progressive severe lymphopenia in C57BL/6 mice due to increased apoptosis rates. T-cell depletion did not occur in gamma interferon (IFN-gamma)-deficient mice which showed increased T-cell numbers and proliferation; in contrast, deficiency in nitric oxide synthase 2 did not prevent T-cell loss. Although T-cell loss was IFN-gamma dependent, expression of the IFN-gamma receptor on T cells was not required for depletion. Similarly, while T-cell loss was optimal if the T cells expressed IFN-gamma, CD8(+) T-cell depletion could occur in the absence of T-cell-derived IFN-gamma. Depletion did not require that the T cells be specific for mycobacterial antigen and was not affected by deficiencies in the tumor necrosis factor receptors p55 or p75, the Fas receptor (CD95), or the respiratory burst enzymes or by forced expression of bcl-2 in hematopoietic cells.     

Central role for B lymphocytes and CD4+ T cells in immunity to infection by the attaching and effacing pathogen Citrobacter rodentium

Citrobacter rodentium, an attaching-effacing bacterial pathogen, establishes an acute infection of the murine colonic epithelium and induces a mild colitis in immunocompetent mice. This study describes the role of T-cell subsets and B lymphocytes in immunity to C. rodentium. C57Bl/6 mice orally infected with C. rodentium resolved infection within 3 to 4 weeks. Conversely, systemic and colonic tissues of RAG1(-/-) mice orally infected with C. rodentium contained high and sustained pathogen loads, and in the colon this resulted in a severe colitis. C57Bl/6 mice depleted of CD4(+) T cells, but not CD8(+) T cells, were highly susceptible to infection and also developed severe colitis. Mice depleted of CD4(+) T cells also had diminished immunoglobulin G (IgG) and IgA antibody responses to two C. rodentium virulence-associated determinants, i.e., EspA and intimin, despite having a massively increased pathogen burden. Mice with an intact T-cell compartment, but lacking B cells ( micro MT mice), were highly susceptible to C. rodentium infection. Systemic immunity, but not mucosal immunity, could be restored by adoptive transfer of convalescent immune sera to infected micro MT mice. Adoptive transfer of immune B cells, but not na?ve B cells, provided highly variable immunity to recipient micro MT mice. The results suggest that B-cell-mediated immune responses are central to resolution of a C. rodentium infection but that the mechanism through which this occurs requires further investigation. These data are relevant to understanding immunity to enteric attaching and effacing bacterial pathogens of humans.     

Functional analysis of the CC chemokine receptor 5 (CCR5) on virus-specific CD8+ T cells following coronavirus infection of the central nervous system

Intracranial infection of C57BL/6 mice with mouse hepatitis virus (MHV) results in an acute encephalomyelitis followed by a demyelinating disease similar in pathology to the human disease multiple sclerosis (MS). T cells participate in both defense and disease progression following MHV infection. Expression of chemokine receptors on activated T cells is important in allowing these cells to traffic into and accumulate within the central nervous system (CNS) of MHV-infected mice. The present study evaluated the contributions of CCR5 to the activation and trafficking of virus-specific CD8(+) T cells into the MHV-infected CNS mice. Comparable numbers of virus-specific CD8(+) T cells derived from immunized CCR5(+/+) or CCR5(-/-) mice were present within the CNS of MHV-infected RAG1(-/-) mice following adoptive transfer, indicating that CCR5 is not required for trafficking of these cells into the CNS. RAG1(-/-) recipients of CCR5(-/-)-derived CD8(+) T cells exhibited a modest, yet significant (P 相似文献   

Enhanced lung injury and delayed clearance of Pneumocystis carinii in surfactant protein A-deficient mice: attenuation of cytokine responses and reactive oxygen-nitrogen species

Surfactant protein A (SP-A), a member of the collectin family, selectively binds to Pneumocystis carinii and mediates interactions between pathogen and host alveolar macrophages in vitro. To test the hypothesis that mice lacking SP-A have delayed clearance of Pneumocystis organisms and enhanced lung injury, wild-type C57BL/6 (WT) and SP-A-deficient mice (SP-A(-/-)) with or without selective CD4(+)-T-cell depletion were intratracheally inoculated with Pneumocystis organisms. Four weeks later, CD4-depleted SP-A-deficient mice had developed a more severe Pneumocystis infection than CD4-depleted WT (P. carinii pneumonia [PCP] scores of 3 versus 2, respectively). Whereas all non-CD4-depleted WT mice were free of PCP, intact SP-A(-/-) mice also had evidence of increased organism burden. Pneumocystis infection in SP-A-deficient mice was associated histologically with enhanced peribronchial and/or perivascular cellularity (score of 4 versus 2, SP-A(-/-) versus C57BL/6 mice, respectively) and a corresponding increase in bronchoalveolar lavage (BAL) cell counts. Increases in SP-D content, gamma interferon, interleukin-4, interleukin-5, and tumor necrosis factor alpha in BAL fluid occurred but were attenuated in PCP-infected SP-A(-/-) mice compared to WT mice. There were increases in total BAL NO levels in both infected groups, but nitrite levels were higher in SP-A(-/-) mice, indicating a reduction in production of higher oxides of nitrogen that was also reflected in lower levels of 3-nitrotyrosine staining in the SP-A(-/-) group. We conclude that despite increases in inflammatory cells, SP-A-deficient mice infected with P. carinii exhibit an enhanced susceptibility to the organism and attenuated production of proinflammatory cytokines and reactive oxygen-nitrogen species. These data support the concept that SP-A is a local effector molecule in the lung host defense against P. carinii in vivo.     

Role for T cell-independent B cell activity in the resolution of primary rotavirus infection in mice.

We examined the importance of T cell-independent B cell activity in the resolution of primary murine (EDIM) rotavirus infection in adult mice. We showed that Rag 1 (C57BL / 6 background) and Rag 2 (BALB / c background) knockout mice, which lack both T and B cells, chronically shed high levels of rotavirus Ag in stool samples following oral inoculation. However, nude mice (BALB / c and C57BL / 6 backgrounds) and alpha beta TCR knockout mice (C57BL / 6 background) chronically shed 100-fold lower levels of virus in stool samples. Thus, B cells appeared to sharply reduce the level of chronic rotavirus shedding by a T cell-independent mechanism. C57BL / 6 mice depleted of CD4(+) cells or both CD4(+) and CD8(+) cells were also unable to resolve primary rotavirus infection but chronically shed equally low levels of rotavirus Ag in stool samples, whereas mice depleted of only CD8(+) cells resolved infection. Similar results were obtained with a second rotavirus strain (EC(w)) in which virus was shed chronically in stool samples at low levels in alpha beta TCR knockout mice and at high levels in Rag 1 knockout mice. Virus-specific intestinal IgA was readily detected in mice lacking thymic T cells and alpha beta T cells and in mice depleted of CD4(+) cells but levels were 95 % reduced in comparison to immunocompetent control mice. Together, these results show that B cells lacking CD4(+) T cell help have the capacity to substantially reduce rotavirus shedding, possibly through the production of T cell-independent IgA to rotavirus, but full resolution requires alpha beta T cells.     

Importance of CD8(+)Vbeta8(+) T cells in IFN-gamma-mediated prevention of toxoplasmic encephalitis in genetically resistant BALB/c mice.

In our attempt to identify a major T cell population(s) that recognizes protective Toxoplasma gondii antigens and produces interferon-gamma (IFN-gamma) for prevention of toxoplasmic encephalitis (TE), we found T cell receptor Vbeta8(+) cells to be the most frequent IFN-gamma-producing population infiltrated into the brain of T. gondii-infected BALB/c mice genetically resistant to the disease. To examine the role of IFN-gamma production by this T cell population for resistance, we transferred Vbeta8(+) immune T cells purified from spleens of infected BALB/c and IFN-gamma(/) mice into infected, sulfadiazine-treated, athymic nude mice. After discontinuation of sulfadiazine treatment, control nude mice that had not received any T cells and animals that had received Vbeta8(+) T cells from IFN-gamma(/) mice all died because of reactivation of infection (TE). In contrast, animals that had received the cells from BALB/c mice survived. Thus, IFN-gamma production by Vbeta8(+) T cells plays an important role in prevention of TE in these animals. When Vbeta8(+) immune T cells were divided into CD4(+) and CD8(+) subsets, a potent protective activity was observed only in the CD8(+) subset, whereas a combination of both subsets provided greater protection than did the CD8(+)Vbeta8(+) population alone. These results indicate that the CD8(+) subset of Vbeta8(+) T cells is a major afferent limb of IFN-gamma-mediated resistance of BALB/c mice against TE, although the CD4(+) subset of the T cell population works additively or synergistically with the CD8(+)Vbeta8(+) population.     

CD8+-T-Cell Immunity against Toxoplasma gondii Can Be Induced but Not Maintained in Mice Lacking Conventional CD4+ T Cells

T-cell immunity is critical for survival of hosts infected with Toxoplasma gondii. Among the cells in the T-cell population, CD8(+) T cells are considered the major effector cells against this parasite. It is believed that CD4(+) T cells may be crucial for induction of the CD8(+)-T-cell response against T. gondii. In the present study, CD4(-/-) mice were used to evaluate the role of conventional CD4(+) T cells in the immune response against T. gondii infection. CD4(-/-) mice infected with T. gondii exhibited lower gamma interferon (IFN-gamma) messages in the majority of their tissues. As a result, mortality due to a hyperinflammatory response was prevented in these animals. Interestingly, T. gondii infection induced a normal antigen-specific CD8(+)-T-cell immune response in CD4(-/-) mice. No difference in generation of precursor cytotoxic T lymphocytes (pCTL) or in IFN-gamma production by the CD8(+)-T-cell populations from the knockout and wild-type animals was observed. However, the mutant mice were not able to sustain CD8(+)-T-cell immunity. At 180 days after infection, the CD8(+)-T-cell response in the knockout mice was depressed, as determined by pCTL and IFN-gamma assays. Loss of CD8(+)-T-cell immunity at this time was confirmed by adoptive transfer experiments. Purified CD8(+) T cells from CD4(-/-) donors that had been immunized 180 days earlier failed to protect the recipient mice against a lethal infection. Our study demonstrated that although CD8(+)-T-cell immunity can be induced in the absence of conventional CD4(+) T cells, it cannot be maintained without such cells.     

Gamma interferon responses of CD4 and CD8 T-cell subsets are quantitatively different and independent of each other during pulmonary Mycobacterium bovis BCG infection

Gamma interferon (IFN-gamma) is a key cytokine in host defense against intracellular mycobacterial infection. It has been believed that both CD4 and CD8 T cells are the primary sources of IFN-gamma. However, the relative contributions of CD4 and CD8 T-cell subsets to IFN-gamma production and the relationship between CD4 and CD8 T-cell activation have not been examined. By using a model of pulmonary mycobacterial infection and various immunodetection assays, we found that CD4 T cells mounted a much stronger IFN-gamma response than CD8 T cells at various times after mycobacterial infection, and this pronounced IFN-gamma production by CD4 T cells was attributed to both greater numbers of antigen-specific CD4 T cells and a greater IFN-gamma secretion capacity of these cells. By using major histocompatibility complex class II-deficient or CD4-deficient mice, we found that the lack of CD4 T cells did not negatively affect primary or secondary CD8 T-cell IFN-gamma responses. The CD8 T cells activated in the absence of CD4 T cells were capable of immune protection against secondary mycobacterial challenge. Our results suggest that, whereas both CD4 and CD8 T cells are capable of IFN-gamma production, the former represent a much greater cellular source of IFN-gamma. Moreover, during mycobacterial infection, CD8 T-cell IFN-gamma responses and activation are independent of CD4 T-cell activation.     

AsialoGM1+CD8+ central memory-type T cells in unimmunized mice as novel immunomodulator of IFN-gamma-dependent type 1 immunity

In unimmunized specific pathogen-free mice, there are unique memory-type CD8(+) T cell populations expressing asialoGM1 (ASGM1). These cells were classified into central memory-type T cells (T(CMT)) judging from their expression profile of CD44, IL-2Rbeta, CD62L and CCR7 cell-surface molecules. Among CD44(high)CD8(+) so-called memory CD8(+) T cell population, ASGM1(+)CD44(high)CD8(+) T(CMT), but not ASGM1(-)CD44(high)CD8(+) memory T cells, produced IFN-gamma by stimulation with anti-CD3 mAb. The physiological significance of ASGM1(+)CD8(+) T(CMT) as early source of IFN-gamma was also demonstrated in vivo. Namely, intravenous injection of anti-CD3 mAb (2 microg) resulted in early activation of IFN-gamma-producing ASGM1(+)CD8(+) T(CMT) cells as well as NKT and NK cells. Unexpectedly, however, few IFN-gamma-producing CD4(+) T cells were detected until 4 h after anti-CD3 mAb administration. Thus, ASGM1(+)CD8(+) T(CMT) were demonstrated to be early IFN-gamma producer, which may be crucial for T(h)1-dependent cellular immunity. Indeed, co-culture of naive CD4(+) T cells with ASGM1(+)CD8(+) T(CMT) but not ASGM1(-)CD8(+) T cells caused a great acceleration of IFN-gamma-producing T(h)1 cells in vitro. Finally, we found that T(h)1-prone C57BL/6 mice possessed higher percentage (10%) of ASGM1(+)CD8(+) T(CMT) in CD8(+) T cells compared with that (3%) of T(h)2-prone BALB/c mice. Moreover, ASGM1(+)CD8(+) T(CMT) derived from C57BL/6 mice produced higher levels of IFN-gamma compared with those from BALB/c mice. Thus, ASGM1(+)CD8(+) T(CMT), whose differentiation in vivo is genetically controlled, appear to play a critical role in the control of type 1 immunity, which is essential for therapy of tumors and infectious diseases.