CD8 +

MHC-restricted CD8(+) T cells are important during infection with the intracellular protozoan parasite Trypanosoma cruzi, the causative agent of Chagas disease. Experimental studies performed in the past 25 years have elucidated a number of features related to the immune response mediated by these T cells, which are important for establishing the parasite/host equilibrium leading to chronic infection. CD8(+) T cells are specific for highly immunodominant antigens expressed by members of the trans-sialidase family. After infection, their activation is delayed, and the cells display a high proliferative activity associated with high apoptotic rates. Although they participate in parasite control and elimination, they are unable to clear the infection due to their low fitness, allowing the parasite to establish the chronic phase when these cells then play an active role in the induction of heart immunopathology. Vaccination with a number of subunit recombinant vaccines aimed at eliciting specific CD8(+) T cells can reverse this path, thereby generating a productive immune response that will lead to the control of infection, reduction of symptoms, and reduction of disease transmission. Due to these attributes, activation of CD8(+) T lymphocytes may constitute a path for the development of a veterinarian or human vaccine.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)UNIFESP Escola Paulista Med, Ctr Terapia Celular & Mol CTCMol, BR-04044010 São Paulo, BrazilUniversidade Federal de São Paulo, Escola Paulista Med, Dept Microbiol Imunol & Parasitol, BR-04044010 São Paulo, BrazilUNIFESP, Inst Saude & Sociedade, Dept Biociencias, BR-11015020 Santos, SP, BrazilUNIFESP Escola Paulista Med, Ctr Terapia Celular & Mol CTCMol, BR-04044010 São Paulo, BrazilUniversidade Federal de São Paulo, Escola Paulista Med, Dept Microbiol Imunol & Parasitol, BR-04044010 São Paulo, BrazilUNIFESP, Inst Saude & Sociedade, Dept Biociencias, BR-11015020 Santos, SP, BrazilFAPESP: 2009/06820-4FAPESP: 2013/13668-0FAPESP: 2012/22514-3Web of Scienc

TLR3 Is a Negative Regulator of Immune Responses Against Paracoccidioides brasiliensis

Toll-like receptors (TLRs) comprise the best-characterized pattern-recognition receptor (PRR) family able to activate distinct immune responses depending on the receptor/adaptor set assembled. TLRs, such as TLR2, TLR4 and TLR9, and their signaling were shown to be important in Paracoccidioides brasiliensis infections. However, the role of the endosomal TLR3 in experimental paracoccidioidomycosys remains obscure. In vitro assays, macrophages of the bone marrow of WT or TLR3−/− mice were differentiated for evaluation of their microbicidal activity. In vivo assays, WT or TLR3−/− mice were infected intratracheally with Paracoccidioides brasiliensis yeasts for investigation of the lung response type induced. The cytotoxic activity of CD8+ T cells was assessed by cytotoxicity assay. To confirm the importance of CD8+ T cells in the control of infection in the absence of tlr3, a depletion assay of these cells was performed. Here, we show for the first time that TLR3 modulate the infection against Paracoccidioides brasiliensis by dampening pro-inflammatory response, NO production, IFN+CD8+T, and IL-17+CD8+T cell activation and cytotoxic function, associated with granzyme B and perforin down regulation. As conclusion, we suggest that TLR3 could be used as an escape mechanism of the fungus in an experimental paracoccidioidomycosis

Subdominant/Cryptic CD8 T Cell Epitopes Contribute to Resistance against Experimental Infection with a Human Protozoan Parasite

During adaptive immune response, pathogen-specific CD8+ T cells recognize preferentially a small number of epitopes, a phenomenon known as immunodominance. Its biological implications during natural or vaccine-induced immune responses are still unclear. Earlier, we have shown that during experimental infection, the human intracellular pathogen Trypanosoma cruzi restricts the repertoire of CD8+ T cells generating strong immunodominance. We hypothesized that this phenomenon could be a mechanism used by the parasite to reduce the breath and magnitude of the immune response, favoring parasitism, and thus that artificially broadening the T cell repertoire could favor the host. Here, we confirmed our previous observation by showing that CD8+ T cells of H-2a infected mice recognized a single epitope of an immunodominant antigen of the trans-sialidase super-family. In sharp contrast, CD8+ T cells from mice immunized with recombinant genetic vaccines (plasmid DNA and adenovirus) expressing this same T. cruzi antigen recognized, in addition to the immunodominant epitope, two other subdominant epitopes. This unexpected observation allowed us to test the protective role of the immune response to subdominant epitopes. This was accomplished by genetic vaccination of mice with mutated genes that did not express a functional immunodominant epitope. We found that these mice developed immune responses directed solely to the subdominant/cryptic CD8 T cell epitopes and a significant degree of protective immunity against infection mediated by CD8+ T cells. We concluded that artificially broadening the T cell repertoire contributes to host resistance against infection, a finding that has implications for the host-parasite relationship and vaccine development

Pathogen-Induced Proapoptotic Phenotype and High CD95 (Fas) Expression Accompany a Suboptimal CD8+ T-Cell Response: Reversal by Adenoviral Vaccine

MHC class Ia-restricted CD8+ T cells are important mediators of the adaptive immune response against infections caused by intracellular microorganisms. Whereas antigen-specific effector CD8+ T cells can clear infection caused by intracellular pathogens, in some circumstances, the immune response is suboptimal and the microorganisms survive, causing host death or chronic infection. Here, we explored the cellular and molecular mechanisms that could explain why CD8+ T cell-mediated immunity during infection with the human protozoan parasite Trypanosoma cruzi is not optimal. For that purpose, we compared the CD8+ T-cell mediated immune responses in mice infected with T. cruzi or vaccinated with a recombinant adenovirus expressing an immunodominant parasite antigen. Several functional and phenotypic characteristics of specific CD8+ T cells overlapped. Among few exceptions was an accelerated expansion of the immune response in adenoviral vaccinated mice when compared to infected ones. Also, there was an upregulated expression of the apoptotic-signaling receptor CD95 on the surface of specific T cells from infected mice, which was not observed in the case of adenoviral-vaccinated mice. Most importantly, adenoviral vaccine provided at the time of infection significantly reduced the upregulation of CD95 expression and the proapoptotic phenotype of pathogen-specific CD8+ cells expanded during infection. In parallel, infected adenovirus-vaccinated mice had a stronger CD8 T-cell mediated immune response and survived an otherwise lethal infection. We concluded that a suboptimal CD8+ T-cell response is associated with an upregulation of CD95 expression and a proapoptotic phenotype. Both can be blocked by adenoviral vaccination

CD8+ T Cell-Mediated Immunity during Trypanosoma cruzi Infection: A Path for Vaccine Development?

MHC-restricted CD8+ T cells are important during infection with the intracellular protozoan parasite Trypanosoma cruzi, the causative agent of Chagas disease. Experimental studies performed in the past 25 years have elucidated a number of features related to the immune response mediated by these T cells, which are important for establishing the parasite/host equilibrium leading to chronic infection. CD8+ T cells are specific for highly immunodominant antigens expressed by members of the trans-sialidase family. After infection, their activation is delayed, and the cells display a high proliferative activity associated with high apoptotic rates. Although they participate in parasite control and elimination, they are unable to clear the infection due to their low fitness, allowing the parasite to establish the chronic phase when these cells then play an active role in the induction of heart immunopathology. Vaccination with a number of subunit recombinant vaccines aimed at eliciting specific CD8+ T cells can reverse this path, thereby generating a productive immune response that will lead to the control of infection, reduction of symptoms, and reduction of disease transmission. Due to these attributes, activation of CD8+ T lymphocytes may constitute a path for the development of a veterinarian or human vaccine

Relevance of long-lived CD8+ T effector memory (TEM) cells for protective immunity elicited by heterologous prime-boost vaccination.

Owing to the importance of major histocompatibility complex class Ia–restricted CD8+ T cells for host survival following viral, bacterial, fungal, or parasitic infection, it has become largely accepted that these cells should be considered in the design of a new generation of vaccines. For the past 20 years, solid evidence has been provided that the heterologous prime-boost regimen achieves the best results in terms of induction of long-lived protective CD8+ T cells against a variety of experimental infections. Although this regimen has often been used experimentally, as is the case for many vaccines, the mechanism behind the efficacy of this vaccination regimen is still largely unknown. The main purpose of this review is to examine the characteristics of the protective CD8+ T cells generated by this vaccination regimen. Part of its efficacy certainly relies on the generation and maintenance of large numbers of specific lymphocytes. Other specific characteristics may also be important, and studies on this direction have only recently been initiated. So far, the characterization of these protective, long-lived T cell populations suggests that there is a high frequency of polyfunctional T cells; these cells cover a large breadth and display a T effector memory (TEM) phenotype. These TEM cells are capable of proliferating after an infectious challenge and are highly refractory to apoptosis due to a control of the expression of pro-apoptotic receptors such as CD95. Also, they do not undergo significant long-term immunological erosion. Understanding the mechanisms that control the generation and maintenance of the protective activity of these long-lived TEM cells will certainly provide important insights into the physiology of CD8+ T cells and pave the way for the design of new or improved vaccines.

Swimming Against the Current: Genetic Vaccination Against Trypanosoma Cruzi Infection in Mice

Vaccines have had an unquestionable impact on public health during the last century. The most likely reason for the success of vaccines is the robust protective properties of specific antibodies. However, antibodies exert a strong selective pressure and many microorganisms, such as the obligatory intracellular parasite Trypanosoma Cruzi , have been selected to survive in their presence. Although the host develops a strong immune response to T. cruzi, they do not clear the infection and instead progress to the chronic phase of the disease. Parasite persistence during the chronic phase of infection is now considered the main factor contributing to the chronic symptoms of the disease. Based on this finding, containment of parasite growth and survival may be one method to avoid the immunopathology of the chronic phase. In this context, vaccinologists have looked over the past 20 years for other immune effector mechanisms that could eliminate these antibody-resistant pathogens. We and others have tested the hypothesis that non-antibody-mediated cellular immune responses (CD4+ Th1 and CD8+ Tc1 cells) to specific parasite antigens/genes expressed by T. cruzi could indeed be used for the purpose of vaccination. This hypothesis was confirmed in different mouse models, indicating a possible path for vaccine development

LFA-1 Mediates Cytotoxicity and Tissue Migration of Specific CD8+ T Cells after Heterologous Prime-Boost Vaccination against Trypanosoma cruzi Infection

Integrins mediate the lymphocyte migration into an infected tissue, and these cells are essential for controlling the multiplication of many intracellular parasites such as Trypanosoma cruzi, the causative agent of Chagas disease. Here, we explore LFA-1 and VLA-4 roles in the migration of specific CD8+ T cells generated by heterologous prime-boost immunization during experimental infection with T. cruzi. To this end, vaccinated mice were treated with monoclonal anti-LFA-1 and/or anti-VLA-4 to block these molecules. After anti-LFA-1, but not anti-VLA-4 treatment, all vaccinated mice displayed increased blood and tissue parasitemia, and quickly succumbed to infection. In addition, there was an accumulation of specific CD8+ T cells in the spleen and lymph nodes and a decrease in the number of those cells, especially in the heart, suggesting that LFA-1 is important for the output of specific CD8+ T cells from secondary lymphoid organs into infected organs such as the heart. The treatment did not alter CD8+ T cell effector functions such as the production of pro-inflammatory cytokines and granzyme B, and maintained the proliferative capacity after treatment. However, the specific CD8+ T cell direct cytotoxicity was impaired after LFA-1 blockade. Also, these cells expressed higher levels of Fas/CD95 on the surface, suggesting that they are susceptible to programmed cell death by the extrinsic pathway. We conclude that LFA-1 plays an important role in the migration of specific CD8+ T cells and in the direct cytotoxicity of these cells

Supplementation of Juçara Berry (<i>Euterpe edulis</i> Mart.) Modulates Epigenetic Markers in Monocytes from Obese Adults: A Double-Blind Randomized Trial

Nutrigenomics is an emerging field in obesity since epigenetic markers can be modified by environmental factors including diet. Considering ju&#231;ara composition&#8212;rich in anthocyanins, monounsaturated fatty acids (MUFAs) and fibers&#8212;it has the potential for epigenetic modulation. We evaluated the ju&#231;ara supplementation modulating the serum fatty acids profile and epigenetic markers in monocytes of adult obese humans. It was a randomized double-blind, controlled trial with 27 obese (Body mass index between 30.0 and 39.9 kg/m2) participants of both genders aged from 31 to 59 years, divided into ju&#231;ara group (5 g ju&#231;ara freeze-dried pulp) or placebo group (5 g of maltodextrin) for 6 weeks. Before and after supplementation, blood samples were collected. The serum and monocytes cells obtained were cultured and stimulated with lipopolysaccharides as proinflammatory stimulus. After 24 h of incubation, the cells and supernatants were collected and analyzed. Ju&#231;ara improved the serum fatty acids profile on unsaturated fatty acids levels. The epigenetic markers evaluated were improved post-treatment. Also, the methylated DNA level was increased after treatment. We find that ju&#231;ara supplementation is a predictor of methyl CpG binding proteins 2 (MeCP2) in monocytes. Concluding, ju&#231;ara supplementation improved the serum fatty acids profile, modulating the epigenetic markers in monocytes from obese individuals