Role of T Helper/Inducer Cells as well as Natural Killer Cells in Resistance to Trypanosoma cruzi Infection

T lymphocytes provide a major line of defence against many protozoan parasites. The aim of this work was to determine the role of T-cell helper/inducer subset (T h/i) in the resistance to Trypanosoma cruzi in a murine model. The importance of natural killer (NK) cells in the resistance to the parasite was also evaluated. BALB/c and C57BL/6 mice were injected with either monoclonal antibodies against L3T4, Thy 1.2, NK1.1, or with a polyclonal rabbit antiserum against NK cells (anti-asialo GM-1). The effect of in vivo administration of these antibodies was tested in separate functional assays. After antibody treatment, mice were infected with a low dose of T. cruzi in the bloodstream form. Mice depleted of, or reduced in T, T h/i, or NK cell activity all developed higher parasitaemia and had higher mortality than their control counterparts. Mice injected with anti-L3T4 monoclonal antibodies were unable to generate a specific antibody response to the parasite. Treatment of mice with alpha/beta interferon, which is known to boost NK cell activity, resulted in an enhanced resistance to the parasite. Our data indicate that T h/i cells as well as NK cells are of vital importance in controlling parasitaemia and reducing mortality in T. cruzi-infected mice. Finally, we also demonstrate that the production of antibodies specific for T. cruzi is strictly T helper cell-dependent.     

PD-1 Expression on Natural Killer Cells and CD8(+) T Cells During Chronic HIV-1 Infection

Abstract Programmed death receptor 1 (PD-1) is an important marker of T-cell exhaustion during HIV-1 infection. Natural killer (NK) cells lose their functional capacity during HIV-1 infection, and PD-1 is expressed on NK cells during other chronic viral and bacterial infections. Here, PD-1 expression was increased on NK cells from both viremic and aviremic HIV-1-seropositive individuals, compared to seronegative controls. However, PD-1 was expressed on a small subset of NK cells and at lower frequency than that observed for CD8(+) T cells. PD-1 was also induced on a minor fraction of NK cells and CD8(+) T cells after long-term culture with IL-15. Raised levels of PD-1 were associated with limited NK cell proliferation, which may have consequences for their maintenance during chronic HIV-1 infection.     

Transient Deficiency of Dendritic Cells Results in Lack of a Merozoite Surface Protein 1-Specific CD4 T Cell Response during Peak Plasmodium chabaudi Blood-Stage Infection

Splenic dendritic cells are crucial for controlling the immune response to malaria by initiating a CD4 gamma interferon (IFN-γ) response early in a blood-stage infection, which contributes to parasite clearance as well as to acute-stage immunopathology. CD8⁻ CD11c^high dendritic cells have been described previously to be important antigen-presenting cells for induction of these CD4 T cell responses in the spleens of Plasmodium chabaudi-infected mice. However, when isolated during the period of maximum parasitemia and shortly thereafter, the dendritic cells transiently lose their ability to stimulate T cells, recovering only as the parasitemia is controlled. This loss of a CD4 T cell response is also observed in vivo during this part of the infection. CD4 T cells from a T cell receptor-transgenic mouse recognizing a peptide of merozoite surface protein 1 (MSP1) injected into BALB/c mice during peak parasitemia proliferate poorly, and very few cells produce IFN-γ and interleukin-2 (IL-2), compared with transgenic T cells injected earlier in the blood-stage infection. CD8⁻ dendritic cells at day 10 can process and present peptides on major histocompatibility complex (MHC) class II with an efficiency similar to that of dendritic cells from earlier in infection. The failure of the day 10 dendritic cells to activate MSP1-specific CD4 T cells fully in vitro is associated with reduced expression of CD86 and lower production of IL-12 rather than with induction of inhibitory DC receptors or production of IL-10.     

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.     

Predominance of CD4 Th1 and CD8 Tc1 Cells Revealed by Characterization of the Cellular Immune Response Generated by Immunization with a DNA Vaccine Containing a Trypanosoma cruzi Gene

Immunization with a plasmid DNA containing the gene encoding the catalytic domain of trans-sialidase (TS) elicits protective immune responses against experimental Trypanosoma cruzi infection. As several studies provided strong evidence that during infection CD4 Th1 and CD8 T cytotoxic type 1 (Tc1) cells are important factors in host resistance, the present study was designed to evaluate which T-cell types were activated in DNA-vaccinated BALB/c mice. We found that bulk cells from DNA-immunized mice had CD4 and CD8 T cells that produced gamma interferon (IFN-gamma) but not interleukin-4 (IL-4) or IL-10. To characterize the TS-specific T cells at the clonal level, we generated CD4 and CD8 clones. We obtained cytotoxic CD4 clones of the Th1 type that secreted large amounts of IFN-gamma but not IL-4 or IL-10. Unexpectedly, we obtained other CD4 clones with a Th2 phenotype, secreting IL-4 and IL-10 but not IFN-gamma. All CD8 clones were cytotoxic and produced IFN-gamma. IL-4 and IL-10 were not secreted by these cells. Using synthetic peptides, we determined a CD8 epitope recognized by several clones as being represented by amino acids IYNVGQVSI. The antiparasitic activity of a CD4 Th1 and a CD8 Tc1 clone was assessed in vitro. CD4 or CD8 T cells significantly inhibited T. cruzi development in infected macrophages or fibroblasts, respectively. We concluded that DNA vaccine efficiently generates potentially protective CD4 Th1 and CD8 Tc1 cells specific for a T. cruzi antigen, therefore reinforcing the possibility of using this strategy for developing a preventive or therapeutic vaccine against Chagas' disease.     

Adhesion of Escherichia coli to HeLa Cells Mediated by Trypanosoma cruzi Surface Glycoprotein-Derived Peptides Inserted in the Outer Membrane Protein LamB

Peptides derived from the surface glycoprotein gp82 of Trypanosoma cruzi, previously implicated in the parasite's invasion of host cells, were expressed as fusions to the protein LamB of Escherichia coli in a region known to be exposed on the cell surface. Bacteria expressing these proteins adhered to HeLa cells in a manner that mimics the pattern of parasite invasion of mammalian cells. Purified LamB fusion proteins were shown to bind to HeLa cells and to inhibit infection by T. cruzi, supporting the notion that these gp82-derived peptides can mediate interaction of the parasite with its host.     

Contribution of NK, NK T, gamma delta T, and alpha beta T cells to the gamma interferon response required for liver protection against Trypanosoma cruzi

In the present work, we show that intracellular Trypanosoma cruzi is rarely found in the livers of acutely infected mice, but inflammation is commonly observed. The presence of numerous intrahepatic amastigotes in infected gamma interferon (IFN-gamma)-deficient mice corroborates the notion that the liver is protected by an efficient local immunity. The contribution of different cell populations was suggested by data showing that CD4- and CD8-deficient mice were able to restrain liver parasite growth. Therefore, we have characterized the liver-infiltrating lymphocytes and determined the sources of IFN-gamma during acute T. cruzi infection. We observed that natural killer (NK) cells increased by day 7, while T and B cells increased by day 14. Among CD3+ cells, CD4+, CD8+, and CD4- CD8- cell populations were greatly expanded. A large fraction of CD3+ cells were positive for PanNK, a beta1 integrin expressed by NK and NK T cells. However, these lymphocytes were not classic NK T cells because they did not express NK1.1 and showed no preferential usage of Vbeta8. Otherwise, liver NK T (CD3+ NK1.1+) cells were not increased in acutely infected mice. The majority of PanNK+ CD4+ and PanNK+ CD8+ cells expressed T-cell receptor alphabeta (TCRalphabeta), whereas PanNK+ CD4- CD8- cells were positive for TCRgammadelta. In fact, gammadelta T cells showed the most remarkable increase (40- to 100-fold) among liver lymphocytes. Most importantly, intracellular analysis revealed high levels of IFN-gamma production at day 7 by NK cells and at day 14 by CD4+, CD8+, and CD4- CD8- TCRgammadelta+ cells. We concluded that NK cells are a precocious source of IFN-gamma in the livers of acutely infected mice, and, as the disease progresses, conventional CD4+ and CD8+ T cells and gammadelta T cells, but not classic NK-T cells, may provide the IFN-gamma required for liver protection against T. cruzi.     

Acute Trypanosoma cruzi infection differentially affects CD3 and Thy-1 mediated T cell activation.

Monoclonal antibodies directed against the Thy-1 molecule or the CD3 complex were used to analyze the activation of T cells from mice acutely infected with Trypanosoma cruzi. When stimulated with G7, a mitogenic anti-Thy-1 monoclonal antibody, spleen cells from infected mice showed a markedly reduced or absent response that could not be restored by varying the culture time or the antibody concentration. However, cells from acutely infected animals proliferated to 145-2C11, an anti-CD3 monoclonal antibody. Flow cytometric analysis showed that the impaired response to G7 could not be attributed to a lack of expression of Thy-1 or CD3. Indeed, G7 seemed to deliver a positive signal to the cells since the proliferative response was completely restored by the addition of PMA. Moreover, purified T cells from infected mice responded to G7 in the presence of accessory cells from uninfected animals. These results suggest that a defective co-stimulatory cell function could be involved in the immunosuppression. In addition, our data present evidence against a generalized T cell anergy in the acute phase of the disease, since CD3-mediated activation was normal.     

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

1. Download : Download high-res image (158KB)
2. Download : Download full-size image

     

SARS-CoV-2-Specific and Functional Cytotoxic CD8 Cells in Primary Antibody Deficiency: Natural Infection and Response to Vaccine

Journal of Clinical Immunology - CD8 cytotoxic T cells (CTLs) play a critical role in the clearance of virally infected cells. SARS-CoV-2-specific CD8 T cells and functional CTLs in natural...     

Immunization of Mice with a TolA-Like Surface Protein of Trypanosoma cruzi Generates CD4+ T-Cell-Dependent Parasiticidal Activity

The gene family encoding a trypomastigote-specific protein restricted to the part of the flagellum in contact with the cell body of the trypomastigote form of Trypanosoma cruzi has been isolated, characterized, and expressed in a baculovirus expression system. The gene family contains three tandemly repeated members that have 97 to 100% sequence identity. The predicted protein encoded by the gene family has both significant amino acid sequence identity and other physical and biological features in common with the TolA proteins of Escherichia coli and Pseudomonas aeruginosa. Based on these similarities, we have designated this gene family tolT. Immunization of mice with recombinant TolT generates a population of CD4(+) T lymphocytes that recognize T. cruzi-infected macrophages, resulting in the production of gamma interferon (IFN-gamma), which leads to NO production and a 50 to 60% reduction in parasite numbers compared to that seen with infected macrophages incubated with naive T cells. This population of T cells also produces both IFN-gamma and interleukin 2 (IL-2) but not IL-4 or IL-5 when incubated with spleen cells stimulated with TolT antigen, indicating that they are of the T-helper 1 type. T cells from mice chronically infected with T. cruzi also produce significant levels of IFN-gamma when cocultured with macrophages and either TolT protein or paraflagellar rod protein, indicating that both of these flagellar proteins produce positive T-cell responses in mice chronically infected with T. cruzi.     

Localization and Developmental Regulation of a Dispersed Gene Family 1 Protein in Trypanosoma cruzi

The dispersed gene family 1 (DGF-1) is the fifth largest gene family in the Trypanosoma cruzi genome, with over 500 members (11). Many of the predicted DGF-1 protein products have several transmembrane domains and N-glycosylation and phosphorylation sites and were thought to localize in the plasma membrane. Here, we report that affinity-purified antibodies against a region of one of these proteins (DGF-1.2) localized it intracellularly in different stages of the parasite. DGF-1.2 is more abundant in the amastigote stage than in trypomastigotes and epimastigotes, as detected by immunofluorescence and Western blot analyses. The protein changed localization during intracellular or extracellular differentiation from the trypomastigote to the amastigote stage, where it finally localized to small bodies in close contact with the inner side of the amastigote plasma membrane. DGF-1.2 did not colocalize with markers of other subcellular organelles, such as acidocalcisomes, glycosomes, reservosomes, lipid droplets, or endocytic vesicles. During extracellular differentiation, the protein was detected in the culture medium from 0 to 22 h, peaking at 14 h. The presence of DGF-1.2 in the differentiation culture medium was confirmed by mass spectrometry analysis. Finally, when epimastigotes were subjected to starvation, there was a decrease in the labeling of the cells and, in Western blots, the appearance of bands of lower molecular mass, suggesting its cleavage. These results represent the first report of direct immunodetection and developmental expression and secretion of a DGF-1 protein.Trypanosoma cruzi is the causative agent of Chagas disease, an endemic illness affecting between 16 and 18 million people in North, Central, and South America for which no vaccine or satisfactory treatment is available (22). During its life cycle, the parasite goes through different stages in the vector (epimastigotes and metacyclic trypomastigotes) and in the mammalian host (amastigotes and bloodstream trypomastigotes). As part of its survival strategy in these varying environments, the parasite has developed a large repertoire of multigene families (9, 11, 12, 16). Among these families, the dispersed gene family 1 (DGF-1) has approximately 565 copies, ranging from 6 to 10 kbp, dispersed throughout the parasite genome (11). The members of the DGF-1 family encode proteins that share 85 to 95% sequence identity (11). Wincker and colleagues first identified clones bearing a common repeated sequence from a T. cruzi genome library (24) and later described the nucleotide sequence of a representative gene (DGF-1.1) (23). They concluded, from in silico studies, that DGF-1 genes encoded putative cell surface proteins (23). In 2005, Kim and colleagues (16) described a new member of this family (DGF-1.2) located in the subtelomeric region of a T. cruzi chromosome surrounded by mainly two kinds of sequences: genes encoding the trans-sialidase (TS) and retrotransposon hot spot (RHS) protein families. The sizes of the open reading frames (ORFs) of DGF-1 genes and their abundance in the T. cruzi genome suggested that they are essential sequences for parasite survival. Furthermore, the existence of some telomeric DGF-1 copies that were always flanked by pseudogenes suggested that these genes have been subjected to strong selective pressure and, as a consequence, that they should be expressed at some life cycle stage of the parasite (16).A glycopeptide shared by several members of the DGF-1 family was recently detected in a glycoproteomic study of T. cruzi trypomastigotes, demonstrating that at least a DGF-1 family member protein is actually expressed and N-glycosylated (3). We also detected a number of peptides corresponding to several DGF-1 family member proteins in a proteomic study of acidocalcisome fractions of epimastigotes of T. cruzi (R. Docampo, J. A. Atwood, R. Tarleton, and R. Orlando, unpublished data). However, this family of proteins has no known orthologs in other species, even in trypanosomatids, and little is known about their localization, expression patterns, and functions in T. cruzi.In the present work, we prepared affinity-purified antibodies against a peptide of the DGF-1.2 protein and investigated its subcellular localization by immunofluorescence microscopy. We also used mass spectrometry (MS) to identify specific peptides recognized by anti-DGF-1.2 antibodies by using fingerprinting analysis.We found that the antibodies preferentially labeled amastigotes. The localization of the protein was in intracellular bodies and not on the cell surface and changed during amastigote development. During the in vitro trypomastigote-to-amastigote transition, we detected continuous secretion of DGF-1.2 into the medium, peaking at 14 h. Anti DGF-1 antibodies that recognized the intracellular protein in both differentiation forms also recognized the secreted protein from trypomastigotes and amastigotes. Finally, when epimastigotes were subjected to starvation, there was a decrease in labeling of the cells and the appearance of defined bands of smaller molecular mass in Western blots, suggesting its cleavage.     

Regulatory T Cells in the Antibody Response to Haemophilus influenzae Type b Polysaccharide

An in vitro culture system for the induction of an antipolysaccharide response was used to study the cellular interactions which determine the magnitude and nature of this B-lymphocyte response. Healthy adult volunteers were vaccinated with the Haemophilus influenzae type b polysaccharide (PRP)-tetanus toxoid (TT) conjugate vaccine. Optimal in vitro anti-PRP and anti-TT antibody responses were obtained when B cells were cultured with equal amounts of T cells. The in vitro response is antigen dependent and antigen specific. Culturing with PRP mixed with TT in the presence of T cells induces the highest number of anti-PRP antibody-secreting cells (ASC) (128.4 ×/÷ 15.9 [geometric mean ×/÷ standard deviation] immunoglobulin M [IgM] anti-PRP ASC/10⁶ cells; 9.3 ×/÷ 7.6 IgG anti-PRP ASC/10⁶ cells). Culturing without T cells induced no anti-PRP ASC; culturing with only PRP, in the presence of T cells, yielded low numbers of anti-PRP ASC (3.7 ×/÷ 5.2 IgM anti-PRP ASC/10⁶ cells and 1.2 ×/÷ 2.2 IgG anti-PRP ASC/10⁶ cells). Transwell studies showed that the requirements for the antibody response against the polysaccharide are different from those of an antiprotein response. Cytokines formed as a consequence of contact between protein-specific B and T cells were on their own not sufficient to activate TT-specific B cells (8.4 ×/÷ 1.4 anti-TT ASC/10⁶ cells); direct contact between T and B cells appeared to be an absolute requirement. However, physical contact between B and T cells in one compartment of the Transwell system resulted in the release of soluble factors able to stimulate B cells in the other compartment to secrete antipolysaccharide antibodies (164 ×/÷ 1.6 anti-PRP ASC/10⁶ cells).     

Both CD1d antigen presentation and interleukin-12 are required to activate natural killer T cells during Trypanosoma cruzi infection

Mechanisms of natural killer T (NKT)-cell activation remain unclear. Here, we report that during Trypanosoma cruzi infection, interleukin-12 (IL-12) deficiency or anti-CD1d antibody treatment prevents normal activation. The required IL-12 arises independently of MyD88. The data support a model of normal NKT-cell activation that requires IL-12 and TCR stimulation.     

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.     

B cells modulate T cells so as to favour T helper type 1 and CD8+ T-cell responses in the acute phase of Trypanosoma cruzi infection

In this study, we have evaluated the production of pro- and anti-inflammatory cytokines and the formation of central and effector memory T cells in mice lacking mature B cells (mu MT KO). The results show that Trypanosoma cruzi infection in C57Bl/6m mu MT KO mice is intensified in relation to control mice and this exacerbation is related to low levels of inflammatory cytokines produced during the acute infection and the lower numbers of central and effector memory CD4(+) and CD8(+) T cells generated during the acute phase of the infection. In addition, a marked reduction in the CD8(+) T-cell subpopulation was observed in mu MT KO infected mice. In agreement to this, the degree of tissue parasitism was increased in mu MT mice and the tissue inflammatory response was much less intense in the acute phase of the infection, consistent with a deficit in the generation of effector T cells. Flow cytometry analysis of the skeletal muscle inflammatory infiltrate showed a predominance of CD8(+) CD45Rb low in B-cell-sufficient C57Bl/6 mice, whereas the preponderant cell type in mu MT KO skeletal muscle inflammatory infiltrate was CD4(+) T cells. In addition, CD8(+) T cells found in skeletal muscle from mu MT KO infected mice were less activated than in control B-cell sufficient infected mice. These results suggest that B cells may participate in the generation of effector/memory T cells. In addition and more importantly, B cells were crucial in the maintenance of central and effector memory CD8(+) T cell, as well as the determination of the T cell cytokine functional pattern, and they may therefore account for critical aspects of the resistance to intracellular pathogens, such as T. cruzi.     

Cellular Response to Basic Protein and T Suppressor Cells in Multiple Sclerosis

Peripheral blood lymphocytes from patients with multiple sclerosis (MS) and two control groups, patients with neurologic diseases other than MS and healthy individuals, were examined for their cellular response to basic protein (BP), suppressor cell activity elicited by concanavalin A (ConA) and enumeration of Ty cells. Lymphocytes from patients with active and chronic progressive MS showed the highest blastogenic stimulation in response to BP, the lowest ConA-induced suppression and the lowest absolute and relative number of Tγ cells. Lymphocytes from patients with non-active or slowly progressive MS showed BP blastogenic stimulation similar to or slightly higher than that of the control groups. The ConA suppressor activity and the absolute and relative number of Tγ cells in the nonactive MS group were within normal ranges. The results indicate that although hypersensitivity to BP may be accompanied by deficient immunoregulatory activity, there is no pattern in the sequence of events. In addition, in some instances, changes in the immunoregulatory cells occurred with little or no effect on the cellular response to the neural antigen.     

Cellular Response to Basic Protein and T Suppressor Cells in Multiple Sclerosis

Peripheral blood lymphocytes from patients with multiple sclerosis (MS) and two control groups, patients with neurologic diseases other than MS and healthy individuals, were examined for their cellular response to basic protein (BP), suppressor cell activity elicited by concanavalin A (ConA) and enumeration of Ty cells. Lymphocytes from patients with active and chronic progressive MS showed the highest blastogenic stimulation in response to BP, the lowest ConA-induced suppression and the lowest absolute and relative number of Tγ cells. Lymphocytes from patients with non-active or slowly progressive MS showed BP blastogenic stimulation similar to or slightly higher than that of the control groups. The ConA suppressor activity and the absolute and relative number of Tγ cells in the nonactive MS group were within normal ranges. The results indicate that although hypersensitivity to BP may be accompanied by deficient immunoregulatory activity, there is no pattern in the sequence of events. In addition, in some instances, changes in the immunoregulatory cells occurred with little or no effect on the cellular response to the neural antigen.     

The Fas death pathway controls coordinated expansions of type 1 CD8 and type 2 CD4 T cells in Trypanosoma cruzi infection

We investigated the role of the Fas ligand (FasL)/Fas death pathway on apoptosis and cytokine production by T cells in Trypanosoma cruzi infection. Anti-FasL, but not anti-TNF-alpha or anti-TRAIL, blocked activation-induced cell death of CD8 T cells and increased secretion of IL-10 and IL-4 by CD4 T cells from T. cruzi-infected mice. CD4 and CD8 T cells up-regulated Fas/FasL expression during T. cruzi infection. However, Fas expression increased earlier in CD8 T cells, and a higher proportion of CD8 T cells was activated and expressed IFN-gamma compared with CD4 T cells. Injection of anti-FasL in infected mice reduced parasitemia and CD8 T cell apoptosis and increased the ratio of CD8:CD4 T cells recovered from spleen and peritoneum. FasL blockade increased the number of activated T cells, enhanced NO production, and reduced parasite loads in peritoneal macrophages. Injection of anti-FasL increased IFN-gamma secretion by splenocytes responding to T. cruzi antigens but also exacerbated production of type 2 cytokines IL-10 and IL-4 at a late stage of acute infection. These results indicate that the FasL/Fas death pathway regulates apoptosis and coordinated cytokine responses by type 1 CD8 and type 2 CD4 T cells in T. cruzi infection.