CD8+ T Lymphocytes Are the Major Cell Population Involved in the Early Gamma Interferon Response and Resistance to Acute Primary Toxoplasma gondii Infection in Mice

Gamma interferon (IFN-γ) is known to be a major mediator influencing host defense against Toxoplasma (T.) gondii. To evaluate lymphocyte populations involved in this cytokine-mediated early resistance to T. gondii, the effects of in vivo administration of monoclonal antibodies (MAbs) against T-cell subsets and anti-asialo GM1 antibody on the course of infection and IFN-γ response were investigated in mice infected acutely with this parasitic protozoan. A single injection of anti-CD8 MAb on day ?1 or day 4 severely exacerbated the infection, in accordance with a marked suppression of endogenous IFN-γ production. Moreover, the administration of anti-IFN-γ MAb on day 0 but not later than day 4 resulted in a total abrogation of resistance to T. gondii, suggesting that endogenous IFN-γ produced during the first several days of infection is critical for the generation of antitoxoplasmal resistance in mice. In contrast, no significant increase in mortality was observed when injected with either anti-CD4 MAb or anti-asialo GM1 antibody on day ? 1, while these antibodies reduced significantly the ability of mice to produce IFN-γ. Indeed, simultaneous depletion of CD4⁺ and CD8⁺ cells had no greater suppressive effect on host defense and endogenous IFN-γ production than depletion of CD8⁺ cells alone. Together, these results suggest that CD8⁺ T cells play a central role for resolution of acute toxoplasmosis by participating in endogenous IFN-γ production. The possible role of early produced IFN-γ in the development of protective immune response to T. gondii is also discussed.     

Reduced naïve CD8+ T‐cell priming efficacy in elderly adults

Aging is associated with impaired vaccine efficacy and increased susceptibility to infectious and malignant diseases. CD8⁺ T‐cells are key players in the immune response against pathogens and tumors. In aged mice, the dwindling naïve CD8⁺ T‐cell compartment is thought to compromise the induction of de novo immune responses, but no experimental evidence is yet available in humans. Here, we used an original in vitro assay based on an accelerated dendritic cell coculture system in unfractioned peripheral blood mononuclear cells to examine CD8⁺ T‐cell priming efficacy in human volunteers. Using this approach, we report that old individuals consistently mount quantitatively and qualitatively impaired de novo CD8⁺ T‐cell responses specific for a model antigen. Reduced CD8⁺ T‐cell priming capacity in vitro was further associated with poor primary immune responsiveness in vivo. This immune deficit likely arises as a consequence of intrinsic cellular defects and a reduction in the size of the naïve CD8⁺ T‐cell pool. Collectively, these findings provide new insights into the cellular immune insufficiencies that accompany human aging.     

Parasite Fate and Involvement of Infected Cells in the Induction of CD4+ and CD8+ T Cell Responses to Toxoplasma gondii

During infection with the intracellular parasite Toxoplasma gondii, the presentation of parasite-derived antigens to CD4⁺ and CD8⁺ T cells is essential for long-term resistance to this pathogen. Fundamental questions remain regarding the roles of phagocytosis and active invasion in the events that lead to the processing and presentation of parasite antigens. To understand the most proximal events in this process, an attenuated non-replicating strain of T. gondii (the cpsII strain) was combined with a cytometry-based approach to distinguish active invasion from phagocytic uptake. In vivo studies revealed that T. gondii disproportionately infected dendritic cells and macrophages, and that infected dendritic cells and macrophages displayed an activated phenotype characterized by enhanced levels of CD86 compared to cells that had phagocytosed the parasite, thus suggesting a role for these cells in priming naïve T cells. Indeed, dendritic cells were required for optimal CD4⁺ and CD8⁺ T cell responses, and the phagocytosis of heat-killed or invasion-blocked parasites was not sufficient to induce T cell responses. Rather, the selective transfer of cpsII-infected dendritic cells or macrophages (but not those that had phagocytosed the parasite) to naïve mice potently induced CD4⁺ and CD8⁺ T cell responses, and conferred protection against challenge with virulent T. gondii. Collectively, these results point toward a critical role for actively infected host cells in initiating T. gondii-specific CD4⁺ and CD8⁺ T cell responses.     

Expression of PD‐1/LAG‐3 and cytokine production by CD4+ T cells during infection with Plasmodium parasites

CD4⁺ T cells play critical roles in protection against the blood stage of malarial infection; however, their uncontrolled activation can be harmful to the host. In this study, in which rodent models of Plasmodium parasites were used, the expression of inhibitory receptors on activated CD4⁺ T cells and their cytokine production was compared with their expression in a bacterial and another protozoan infection. CD4⁺ T cells from mice infected with P. yoelii 17XL, P yoelii 17XNL, P. chabaudi, P. vinckei and P. berghei expressed the inhibitory receptors, PD‐1 and LAG‐3, as early as 6 days after infection, whereas those from either Listeria monocytogenes‐ or Leishmania major‐infected mice did not. In response to T‐cell receptor stimulation, CD4⁺ T cells from mice infected with all the pathogens under study produced high concentrations of IFN‐γ. IL‐2 production was reduced in mice infected with Plasmodium species, but not in those infected with Listeria or Leishmania. In vitro blockade of the interaction between PD‐1 and its ligands resulted in increased IFN‐γ production in response to Plasmodium antigens, implying that PD‐1 expressed on activated CD4⁺ T cells actively inhibits T cell immune responses. Studies using Myd88^?/?, Trif^?/? and Irf3^?/? mice showed that induction of these CD4⁺ T cells and their ability to produce cytokines is largely independent of TLR signaling. These studies suggest that expression of the inhibitory receptors PD‐1 and LAG‐3 on CD4⁺ T cells and their reduced IL‐2 production are common characteristic features of Plasmodium infection.

     

Heat Shock Cognate Protein 71-Associated Peptides Function as an Epitope for Toxoplasma gondii-Specific CD4+ CTL

HLA-DR-restricted CD4⁺ cytotoxic T-lymphocyte (CTL) lines specific for Toxoplasma gondii (T. gondii)-infected melanoma cells have been established from peripheral blood lymphocytes (PBLs) of a patient with chronic toxoplasmosis. The role of heat shock cognate protein (HSC) 71 in antigen (Ag) processing and presentation of T. gondii-infected melanoma cells to these CD4⁺ CTL lines was investigated. A human melanoma cell line (P36) pulsed with T. gondii-infected P36 cell-derived HSC71 was lysed by a T. gondii-specific CD4⁺ CTL line (Tx-HSC-1). The Tx-HSC-1 also killed T. gondii-infected P36 cells. The lytic activity of Tx-HSC-1 against P36 cells pulsed with T. gondii-infected P36 cell-derived HSC71 was inhibited by monoclonal antibodies (mAbs) against HSC71. Anti-human leukocyte antigen (HLA)-DR mAb also partially blocked the lytic activity, whereas anti-HLA-A,B,C mAb did not block the lytic activity. In addition, a flow cytometric analysis with these specific mAbs against HSC71 showed HSC71 to be expressed on the cell surface of T. gondii-infected P36 cells as well as uninfected P36 cells. These data indicate that HSC71 molecules are expressed on human melanoma cell line P36, and that HSC71 may play a potential role in Ag presentation and processing of T. gondii-infected P36 cells to CD4⁺ CTL.     

Natural Killer Cell Receptor+ T‐Lymphocytes in Normal and Helicobacter pylori‐Infected Human Gastric Mucosa

Background: Helicobacter pylori infection is associated with development of chronic inflammation and infiltration of immune cells into the gastric mucosa. As unconventional T‐lymphocytes expressing natural killer cell receptors are considered to play central roles in the immune response against infection, a study investigating their frequencies in normal and H. pylori‐infected gastric mucosa was undertaken. Materials and Methods: Flow cytometry was used to quantify T‐cells expressing the natural killer cell markers CD161, CD56, and CD94 in freshly isolated lymphocytes from the epithelial and lamina propria layers of gastric mucosa. Thirteen H. pylori‐positive and 24 H. pylori‐negative individuals were studied. Results: CD94⁺ T‐cells were the most abundant (up to 40%) natural killer receptor‐positive T‐cell population in epithelial and lamina propria layers of H. pylori‐negative gastric mucosa. CD161⁺ T‐cells accounted for about one‐third of all T‐cells in both compartments, but the lowest proportion were of CD56⁺ T‐cells. Compared with H. pylori‐negative mucosa, in H. pylori‐infected mucosa the numbers of CD161⁺ T‐cells were significantly greater (p = .04) in the epithelium, whereas the numbers of CD56⁺ T‐cells were lower (p = .01) in the lamina propria. A minor population (< 2%) of T‐cells in both mucosal layers of H. pylori‐negative subjects were natural killer T‐cells, and whose proportions were not significantly different (p > .05) to those in H. pylori‐infected individuals. Conclusions: The predominance, heterogeneity, and distribution of natural killer cell receptor‐positive T‐cells at different locations within the gastric mucosa reflects a potential functional role during H. pylori infection and warrants further investigation.     

A pathway to cure chronic infection with Toxoplasma gondii through immunological intervention

Toxoplasma gondii, an obligate intracellular protozoan parasite, can establish a chronic infection in the brain by forming tissue cysts. This chronic infection is widespread in humans worldwide including developed countries, with up to one third of the population being estimated to be infected with this parasite. Diagnosis of this chronic infection is usually conducted by serological detection of IgG antibodies against this parasite. Since infected individuals remain positive for these antibodies for years, it has generally been considered that this infection is a lifelong infection. It is also often considered that this chronic infection is “latent” or “quiescent”. However, recent discovery of the capability of perforin-dependent, CD8⁺ T cell-mediated immune responses to eliminate T. gondii cysts in collaboration with phagocytes illustrated dynamic interplays between T. gondii cysts and host immune system during this chronic infection. Importantly, the cytotoxic T cell-mediated protective immunity is able to remove mature cysts of the parasite. It is now clear that chronic T. gondii infection is not “latent” or “quiescent”. Elucidating the mechanisms of the dynamic host-pathogen interactions between the anti-cyst protective immunity and T. gondii cysts and identifying the pathway to appropriately activate anti-cyst CD8⁺ cytotoxic T cells would be able to open a door for eradicating T. gondii cysts and curing chronic infection with this parasite.     

Characterization of age‐associated exhausted CD8+ T cells defined by increased expression of Tim‐3 and PD‐1

Aging is accompanied by altered T‐cell responses that result in susceptibility to various diseases. Previous findings on the increased expression of inhibitory receptors, such as programmed cell death protein 1 (PD‐1), in the T cells of aged mice emphasize the importance of investigations into the relationship between T‐cell exhaustion and aging‐associated immune dysfunction. In this study, we demonstrate that T‐cell immunoglobulin mucin domain‐3 (Tim‐3), another exhaustion marker, is up‐regulated on aged T cells, especially CD8⁺ T cells. Tim‐3‐expressing cells also produced PD‐1, but Tim‐3⁺PD‐1⁺ CD8⁺ T cells had a distinct phenotype that included the expression of CD44 and CD62L, from Tim‐3^?PD‐1⁺ cells. Tim‐3⁺PD‐1⁺ CD8⁺ T cells showed more evident properties associated with exhaustion than Tim‐3^?PD‐1⁺ CD8⁺ T cells: an exhaustion‐related marker expression profile, proliferative defects following homeostatic or TCR stimulation, and altered production of cytokines. Interestingly, these cells produced a high level of IL‐10 and induced normal CD8⁺ T cells to produce IL‐10, which might contribute to immune dysregulation in aged mice. The generation of Tim‐3‐expressing CD8⁺ T cells in aged mice seems to be mediated by encounters with antigens but not by specific infection, based on their high expression of CD49d and their unbiased TCR Vβ usage. In conclusion, we found that a CD8⁺ T‐cell population with age‐associated exhaustion was distinguishable by its expression of Tim‐3. These results provide clues for understanding the alterations that occur in T‐cell populations with age and for improving dysfunctions related to the aging of the immune system.     

T cell-derived interferon-γ is required for host defense to Toxoplasma gondii

Interferon-γ (IFN-γ) is important for host defense against various intracellular organisms including a protozoan pathogen Toxoplasma gondii. Various immune cells are recently shown to produce IFN-γ in T. gondii infection, however, it remains elusive which cell types are important for anti-T. gondii host defense so far. Here we generate a new IFN-γ reporter "GREVEN" mouse line in which a fusion protein of Venus and NanoLuc to analyze IFN-γ producing cells during T. gondii infection and find that CD4⁺, CD8⁺, γδ T cells and natural killer cells express Venus in a time dependent manner. Furthermore, Lck-Cre/Ifng^fl/fl mice are highly susceptible to T. gondii infection. Taken together, our results demonstrate that T cell-derived IFN-γ plays an important role in anti-T. gondii host defense.     

Induction of IL-10-producing regulatory B cells following Toxoplasma gondii infection is important to the cyst formation

Toxoplasma gondii is a protozoan parasite that infects humans and animals via congenital or postnatal routes. During parasite infection, IL-10-producing Bregs are stimulated as part of the parasite-induced host immune responses that favor infection. In this study, we investigated whether T. gondii infection induces immune regulatory cells including IL-10-producing CD1d^highCD5⁺ regulatory B cells (Bregs) and whether Breg induction is critical for the development of chronic infection of T. gondii. Furthermore, B cell-deficient (μMT) mice revealed that the IL-10-producing B cells might be associated with the development of chronic T. gondii infection. To better understand the mechanism underlying the accumulation of IL-10-producing B cells upon T. gondii infection, we determined the effect of products released by T. gondii on the induction and differentiation of IL-10-producing B cells during the acute stage of infection using transgenic green fluorescent protein (GFP)-expressing T. gondii strain. We demonstrated that products secreted at the stage of cell lysis by fully replicated tachyzoites induced the differentiation of naive B cells to IL-10-producing Bregs. Our results indicated that the downregulation of the immune response via Bregs during T. gondii infection is related to cyst formation in the host brain and to the establishment of chronic infection.     

Intranasal immunization with Mycobacterium tuberculosis Rv3615c induces sustained adaptive CD4+ T‐cell and antibody responses in the respiratory tract

Sustained adaptive immunity to pathogens provides effective protection against infections, and effector cells located at the site of infection ensure rapid response to the challenge. Both are essential for the success of vaccine development. To explore new vaccination approach against Mycobacterium tuberculosis (M.tb) infection, we have shown that Rv3615c, identified as ESX‐1 substrate protein C of M.tb but not expressed in BCG, induced a dominant Th1‐type response of CD4⁺ T cells from patients with tuberculosis pleurisy, which suggests a potential candidate for vaccine development. But subcutaneous immunization with Rv3615c induced modest T‐cell responses systemically, and showed suboptimal protection against virulent M.tb challenge at the site of infection. Here, we use a mouse model to demonstrate that intranasal immunization with Rv3615c induces sustained capability of adaptive CD4⁺ T‐ and B‐cell responses in lung parenchyma and airway. Rv3615c contains a dominant epitope of mouse CD4⁺ T cells, Rv3615c_41‐50, and elicits CD4⁺ T‐cell response with an effector–memory phenotype and multi‐Th1‐type cytokine coexpressions. Since T cells resident at mucosal tissue are potent at control of infection at early stage, our data show that intranasal immunization with Rv3615c promotes a sustained regional immunity to M.tb, and suggests a potency in control of M.tb infection. Our study warranties a further investigation of Rv3615c as a candidate for development of effective vaccination against M.tb infection.     

The Dysfunction of CD4+CD25+ Regulatory T Cells Contributes to the Abortion of Mice Caused by Toxoplasma gondii Excreted-Secreted Antigens in Early Pregnancy

Toxoplasma gondii is an opportunistic intracellular parasite that is highly prevalent in human and warm-blooded animals throughout the world, leading to potentially severe congenital infections. Although the abortion caused by T. gondii is believed to be dependent on the timing of maternal infection during pregnancy, the mechanism remains unclear. This study was focused on the effects of T. gondii excreted-secreted antigens on pregnant outcomes and CD4⁺CD25⁺ Foxp3⁺ regulatory T cells at different stages of pregnancy. The results showed that in mice the frequency and suppressive function of CD4⁺CD25⁺ regulatory cells were diminished after injection of T. gondii excreted-secreted antigens at early and intermediate stages of pregnancy. The abortion caused by T. gondii excreted-secreted antigens at early pregnancy could be partly prevented by adoptively transferring of CD4⁺CD25⁺ cells from the mice injected with T. gondii excreted-secreted antigens at late pregnancy, but not from the mice with the same treatment at early pregnancy. Furthermore, T. gondii excreted-secreted antigens induced apoptosis of CD4⁺CD25⁺ regulatory cells of mice in early and intermediate stages of pregnancy by down-regulating their Bcl-2 expressions and Bcl-2/Bax ratio. This study provides new insights into the mechanism that T. gondii infection is the high risk factor for abortion in early pregnancy.     

α2-3 Sialic acid glycoconjugate loss and its effect on infection with Toxoplasma parasites

Recognition of sialylated glycoconjugates is important for host cell invasion by Apicomplexan parasites. Toxoplasma gondii parasites penetrate host cells via interactions between their microneme proteins and sialylated glycoconjugates on the surface of host cells. However, the role played by sialic acids during infection with T. gondii is not well understood. Here, we focused on the role of α2-3 sialic acid linkages as they appear to be widely expressed in vertebrates. Removal of α2-3 sialic acid linkages on macrophages by neuraminidase treatment did not influence the rate of infection or growth of T. gondii, nor did it affect phagocytosis in vitro. Sialyltransferase ST3Gal-I deficient mice (ST3Gal-I^−/− mice) lost α2-3 sialic acid linkages in macrophages and spleen cells. The numbers of T. gondii-infected CD11b⁺ cells in peritoneal cavities of the infected ST3Gal-I^−/− mice were relatively lower than those of the infected wild type animals. In addition, CD8⁺ T cell populations and numbers in the spleens and peritoneal cavities of the ST3Gal-I^−/− mice were significantly lower than those in the wild type animals before and after the T. gondii infection. ST3Gal-I^−/− mice had severe liver damage and reduced survival rates following peritoneal infection with T. gondii. Furthermore, adoptive transfer of immune CD8⁺ cells from wild type mice to ST3Gal-I^−/− mice increased their survival during infection with T. gondii. Our data show that parasite invasion via α2-3 sialic acid linkages might not contribute on host survival and indicate the impact that loss of α2-3 sialic acid linkages has on CD8⁺ T cell populations, which are necessary for effective immune responses against infection with T. gondii.     

Immunoregulation by Toxoplasma gondii infection prevents allergic immune responses in mice

Toxoplasma gondii is a ubiquitous intracellular parasite affecting most mammals including humans. In epidemiological studies, infection with T. gondii and allergy development have been postulated to be inversely related. Using a mouse model of birch pollen allergy we investigated whether infection with T. gondii influences allergic immune responses to birch pollen. BALB/c mice were infected with T. gondii oocysts either before or at the end of sensitisation with the major birch pollen allergen Bet v 1 and thereafter aerosol challenged with birch pollen extract. During the acute phase of infection, clinical signs correlated with increased levels of serum TNF-α, IL-6, IFN-γ and anti-Toxoplasma-IgM. In the chronic phase, Toxoplasma-specific serum IgG, brain tissue cysts and high IFN-γ production in spleen cell cultures were detected. Mice infected prior to allergic sensitisation produced significantly less allergen-specific IgE and IgG1, while IgG2a levels were markedly increased. IL-5 levels in spleen cell cultures and bronchoalveolar lavage fluid were significantly reduced, and airway inflammation was prevented in these mice. Notably, in mice infected at the end of the allergic sensitisation process, systemic and local immune responses to the allergen were markedly reduced. T.gondii infection was associated with up-regulation of Toll-like receptor 2 (TLR2), 4, 9 and 11, as well as T-bet (a differentiation factor for Th1 cells) mRNA expression in splenocytes; moreover, enhanced TGF-β, IL-10 and Foxp3 mRNA expression in these cells suggested that regulatory mechanisms were involved in suppression of the allergic immune response. Kinetic studies confirmed the induction of Foxp3⁺CD4⁺CD25⁺ regulatory T cells preferentially during the chronic phase of T. gondii infection. Our data demonstrate that T. gondii exhibits strong immunomodulating properties which lead to prevention of allergic immune responses and thereby support the hygiene hypothesis.     

Brucella abortus induces intracellular retention of MHC‐I molecules in human macrophages down‐modulating cytotoxic CD8+ T cell responses

Brucella abortus elicits a vigorous Th1 immune response which activates cytotoxic T lymphocytes. However, B. abortus persists in its hosts in the presence of CD8⁺ T cells, establishing a chronic infection. Here, we report that B. abortus infection of human monocytes/macrophages inhibited the IFN‐γ‐induced MHC‐I cell surface expression. This phenomenon was dependent on metabolically active viable bacteria. MHC‐I down‐modulation correlated with the development of diminished CD8⁺ cytotoxic T cell response as evidenced by the reduced expression of the activation marker CD107a on CD8⁺ T lymphocytes and a diminished percentage of IFN‐γ‐producing CD8⁺ T cells. Inhibition of MHC‐I expression was not due to changes in protein synthesis. Rather, we observed that upon B. abortus infection MHC‐I molecules were retained within the Golgi apparatus. Overall, these results describe a novel mechanism based on the intracellular sequestration of MHC‐I molecules whereby B. abortus would avoid CD8⁺ cytotoxic T cell responses, evading their immunological surveillance.     

Human CD8+ T cells transduced with an additional receptor bispecific for both Mycobacterium tuberculosis and HIV‐1 recognize both epitopes

Tuberculosis (TB) and human immunodeficiency virus type 1 (HIV‐1) infection are closely intertwined, with one‐quarter of TB/HIV coinfected deaths among people died of TB. Effector CD8⁺ T cells play a crucial role in the control of Mycobacterium tuberculosis (MTB) and HIV‐1 infection in coinfected patients. Adoptive transfer of a multitude of effector CD8⁺ T cells is an appealing strategy to impose improved anti‐MTB/HIV‐1 activity onto coinfected individuals. Due to extensive existence of heterologous immunity, that is, T cells cross‐reactive with peptides encoded by related or even very dissimilar pathogens, it is reasonable to find a single T cell receptor (TCR) recognizing both MTB and HIV‐1 antigenic peptides. In this study, a single TCR specific for both MTB Ag85B_199‐207 peptide and HIV‐1 Env_120‐128 peptide was screened out from peripheral blood mononuclear cells of a HLA‐A*0201⁺ healthy individual using complementarity determining region 3 spectratype analysis and transferred to primary CD8⁺ T cells using a recombinant retroviral vector. The bispecificity of the TCR gene‐modified CD8⁺ T cells was demonstrated by elevated secretion of interferon‐γ, tumour necrosis factor‐α, granzyme B and specific cytolytic activity after antigen presentation of either Ag85B_199‐207 or Env_120‐128 by autologous dendritic cells. To the best of our knowledge, this study is the first report proposing to produce responses against two dissimilar antigenic peptides of MTB and HIV‐1 simultaneously by transfecting CD8⁺ T cells with a single TCR. Taken together, T cells transduced with the additional bispecific TCR might be a useful strategy in immunotherapy for MTB/HIV‐1 coinfected individuals.     

Induction of protective immunity by primed B-1 cells in Toxoplasma gondii -infected B cell-deficient mice

We examined the role of B‐1 cells in protection against Toxoplasma gondii infection using B cell‐deficient mice (μMT mice). We found that primed but not naïve B‐1 cells from wild‐type C57BL/6 mice protected B cell‐deficient recipients from challenge infection. All μMT mice transferred with primed B‐1 cells survived more than 5 months after T. gondii infection, whereas 100% of μMT mice transferred with naïve B‐1 cells succumbed by 18 days after infection. Additionally, high expression of both T help (Th) 1‐ and Th2‐type cytokines and a high level of nitric oxide production were observed in T. gondii‐infected μMT mice transferred with primed B‐1 cells. Thus, it was clearly demonstrated that B‐1 cells play an important role in host protection against T. gondii infection in μMT mice.     

Characterization of a novel organelle in Toxoplasma gondii with similar composition and function to the plant vacuole

Toxoplasma gondii belongs to the phylum Apicomplexa and is an important cause of congenital disease and infection in immunocompromised patients. Like most apicomplexans, T. gondii possesses several plant‐like features, such as the chloroplast‐like organelle, the apicoplast. We describe and characterize a novel organelle in T. gondii tachyzoites, which is visible by light microscopy and possesses a broad similarity to the plant vacuole. Electron tomography shows the interaction of this vacuole with other organelles. The presence of a plant‐like vacuolar proton pyrophosphatase (TgVP1), a vacuolar proton ATPase, a cathepsin L‐like protease (TgCPL), an aquaporin (TgAQP1), as well as Ca²⁺/H⁺ and Na⁺/H⁺ exchange activities, supports similarity to the plant vacuole. Biochemical characterization of TgVP1 in enriched fractions shows a functional similarity to the respective plant enzyme. The organelle is a Ca²⁺ store and appears to have protective effects against salt stress potentially linked to its sodium transport activity. In intracellular parasites, the organelle fragments, with some markers colocalizing with the late endosomal marker, Rab7, suggesting its involvement with the endocytic pathway. Studies on the characterization of this novel organelle will be relevant to the identification of novel targets for chemotherapy against T. gondii and other apicomplexan parasites as well.     

Tuberculosis patients display a high proportion of CD8+ T cells with a high cytotoxic potential

Tuberculosis (TB) is an infectious disease caused by Mycobacterium tuberculosis (Mtb) and remains a major cause of morbidity and mortality worldwide. In the host's immune response system, T cells play a critical role in mediating protection against Mtb infection, but the role of CD8⁺ T cells is still controversial. We evaluated the phenotypical characterization and cytotoxic ability of CD8⁺ T cells by flow cytometry‐based assay. Cytokine levels in serum were measured by multiplex cytokine assay. Our data show that cells from TB patients have an increased percentage of peripheral blood CD8⁺αβ⁺ T (p = 0.02) and CD56⁺CD8⁺ T (p = 0.02) and a decreased frequency of NKG2D⁺CD8⁺ T (p = 0.02) compared with healthy donors. Unlike CD8⁺ T cells from healthy donors, CD8⁺ T cells from TB patients exhibit greater cytotoxicity, mediated by HLA class I molecules, on autologous monocytes in the presence of mycobacterial antigens (p = 0.005). Finally, TB patients have a proinflammatory profile characterized by serum high level of TNF‐α (p = 0.02) and IL‐8 (p = 0.0001), but, interestingly, IL‐4 (p = 0.002) was also increased compared with healthy donors. Our data show evidence regarding the highly cytotoxic status of CD8⁺ T cells in Mtb infection. These cytotoxic cells restricted to HLA‐A, B, and C could be used to optimize strategies for designing new TB vaccines or for identifying markers of disease progression.     

Rab22a controls MHC‐I intracellular trafficking and antigen cross‐presentation by dendritic cells

Cross‐presentation by MHC class I molecules allows the detection of exogenous antigens by CD8⁺ T lymphocytes. This process is crucial to initiate cytotoxic immune responses against many pathogens (i.e., Toxoplasma gondii) and tumors. To achieve efficient cross‐presentation, dendritic cells (DCs) have specialized endocytic pathways; however, the molecular effectors involved are poorly understood. In this work, we identify the small GTPase Rab22a as a key regulator of MHC‐I trafficking and antigen cross‐presentation by DCs. Our results demonstrate that Rab22a is recruited to DC endosomes and phagosomes, as well as to the vacuole containing T. gondii parasites. The silencing of Rab22a expression did not affect the uptake of exogenous antigens or parasite invasion, but it drastically reduced the intracellular pool and the recycling of MHC‐I molecules. The knockdown of Rab22a also hampered the cross‐presentation of soluble, particulate and T. gondii‐associated antigens, but not the endogenous MHC‐I antigen presentation through the classical secretory pathway. Our findings provide compelling evidence that Rab22a plays a central role in the MHC‐I endocytic trafficking, which is crucial for efficient cross‐presentation by DCs.