A Transgenic Mouse Model Genetically Tags All Activated CD8 T Cells

There is much evidence that T cells may be activated via mechanisms that act independently of direct TCR ligation. Despite this, the question of whether such forms of bystander T cell activation occur during immune responses is hotly debated. To address some outstanding questions, we set up an in vitro system within which to analyze bystander T cell activation in human T cells, in the absence of the possibility for TCR cross-reactivity. In addition, we have investigated the genetic, phenotypic, and functional characteristics of bystander-activated T cells. In this study, we show that bystander T cell activation is, indeed, observed during a specific immune response, and that it occurs preferentially among CD4؉ memory T cells. Furthermore, bystander-activated T cells display a distinct gene expression profile. The mechanism for bystander T cell activation involves soluble factors, and the outcome is an elevated level of apoptosis. This may provide an explanation for the attrition of T cell memory pools of heterologous specificity during immune responses to pathogens such as viruses.

Section: Discussionmentioning

confidence: 99%

Human CD4+ Memory T Cells Are Preferential Targets for Bystander Activation and Apoptosis

Bangs

Baban²,

Cattan³

et al. 2009

“…However, the number and diversity of Ags that are the targets of these responses is likely to be much greater in protozoal infections than in viral or bacterial infections. Any bystander activation that occurs in this response may not be an inherent property of T. cruzi infection but may be a generalized phenomenon of infection due to cross-reactivity of TCR to different peptides and responses of pre-existing memory T cells that respond to cytokines or chemokines produced during the response to pathogens in the absence of TCR ligation (48,49). Finally, the antiparasite CD8 ϩ T cell pool in persistently infected mice maintains properties of both T CM and T EM cells, bolstering the argument that models of T cell memory derived from sterile viral infections may not be applicable to persistent infections.…”

Section: Discussionmentioning

confidence: 99%

Antigen-Specific T Cells Maintain an Effector Memory Phenotype during Persistent Trypanosoma cruzi Infection

Martin

Tarleton

2005

Infection with the protozoan parasite Trypanosoma cruzi is a major cause of morbidity and mortality in Central and South America. Control of acute experimental infection with T. cruzi is dependent on a robust T cell and type 1 cytokine response. However, little evidence exists demonstrating the development and persistence of a potent antiparasite T cell memory response, and there has been much speculation that the majority of the immune response to T. cruzi infection is not directed against the parasite. In this study, we used an experimental mouse model of T. cruzi infection to test both the Ag specificity and the functional and phenotypic characteristics of the responding T cell population. We observed a vigorous antiparasite response from both CD4+ and CD8+ T cells that was maintained in the face of persistent infection. T cells from infected mice also proliferated in response to re-exposure to Ag, and CD8+ T cells underwent spontaneous proliferation when transferred to naive congenic mice, both characteristic of central memory T cells. Interestingly, T cells from infected mice showed significant down-regulation of CD62L, a characteristic associated with an effector memory phenotype. These results suggest that T cells maintained in mice with chronic T. cruzi infection are fully functional memory cells that cannot be easily categorized in the current central/effector memory paradigm.

“…Each mouse was immunized with four nonoverlapping shots that corresponded to a total of 2 g of plasmid DNA/mouse/immunization. At 2.5 days postimmunization, we harvested the draining superficial inguinal lymph nodes (iLNs), made single-cell suspensions by collagenase treatment, and then hypotonically loaded the bulk iLN cells with 1 mM fluorescein digalactopyranoside (FDG; Molecular Probes, Eugene, OR) to detect the DNA vaccine-encoded ␤-gal (24,25). After FDG loading, the cells were stained …”

Section: Flow Cytometry Assay For ␤-Gal ϩ Dcsmentioning

confidence: 99%

The Hybrid Cytomegalovirus Enhancer/Chicken β-Actin Promoter along with Woodchuck Hepatitis Virus Posttranscriptional Regulatory Element Enhances the Protective Efficacy of DNA Vaccines

Garg

Oran

Hon

et al. 2004

Self Cite

DNA vaccines represent a novel and powerful alternative to conventional vaccine approaches. They are extremely stable and can be produced en masse at low cost; more importantly, DNA vaccines against emerging pathogens or bioterrorism threats can be quickly constructed based solely upon the pathogen’s genetic code. The main drawback of DNA vaccines is that they often induce lower immune responses than traditional vaccines, particularly in nonrodent species. Thus, improving the efficacy of DNA vaccines is a critical issue in vaccine development. In this study we have enhanced the efficacy of DNA vaccines by adopting strategies that increase gene expression. We generated influenza-hemagglutinin (HA)-encoding DNA vaccines that contain the hybrid CMV enhancer/chicken β-actin (CAG) promoter and/or the mRNA-stabilizing post-transcriptional regulatory element from the woodchuck hepatitis virus (WPRE). Mice were immunized with these DNA vaccines, and the influenza-HA-specific cellular and humoral immune responses were compared with a conventional, HA-encoding DNA vaccine whose gene expression was driven by the CMV immediate-early promoter (pCMV-HA). CAG promoter-driven DNA vaccines elicited significantly higher humoral and cellular immune responses compared with the pCMV-HA vaccine. DNA vaccines consisting of both CAG and WPRE elements (pCAG-HA-WPRE) induced the highest level of protective immunity, such that immunization with 10-fold lower DNA doses prevented death in 100% of the mice upon lethal viral challenge, whereas all mice immunized with the conventional pCMV-HA vaccine succumbed to influenza infection.