Peripheral tolerance of T lymphocytes
The immune system needs to react efficiently against invading microorganisms and malignant transformation, while at the same time autoimmune reactions against constituents of the host must be avoided. Mechanisms that ensure tissue integrity and functionality against immune reactivity are collectively called immune tolerance.
In the case of T cell tolerance, T cell clones that potentially recognize self antigens with high affinity do not elicit any autoimmune pathology.
Peripheral T cell tolerance is establshed and maintained through different mechanisms. These include clonal deletion (death of autospecific T cell clones), anergy (hyporeactivity against antigens), ignorance for the antigen, and function of regulatory T cells (T regs).
In recent years, it has become clear that deregulation of T cell tolerance contributes to the pathophysiology of autoimmune disease. This led to the development of therapeutic strategies that target specific molecules involved in T cell tolerance (CD40, TNF, B7). Elucidation of basic mechanisms of tolerance induction is the subject of intensive research internationally, since it can reveal novel targets for therapeutic immune intervention
We are studying peripheral CD8 T tolerance against a specific self-antigen that has been introduced to mice by transgenesis. Specifically, we are interested to characterize aspects of CD8 T tolerance both in cellular and molecular level.

Survival and homeostasis of mature T lymphocytes
After completion of their development, mature T lymphocyte exit thymus and seed peripheral lympoid organs, such as lymph nodes, spleen, gut associated lymphoid tissue etc. Various homeostatic mechanisms act in concert to maintain a relative stable number of T cells after different stimuli. Factors that can expand T cell numbers include infection and autoimmunity whereas decrease of T cells is induced by activation-induced cell death, ionizing radiation and some viruses including HIV.
Mechanisms that promote T cell survival and replenishment (homeostatic proliferation) are mainly cytokines (especially IL-7) and weak interactions with self-antigens. On the other hand, contraction of T cell numbers is promoted by death receptors engagement and cytokine deprivation.
Our lab focuses in molecules and pathways mediating survival and homeostatic proliferation of naïve CD8 (cytotoxic) T cells using conventional and T cell receptor (TCR) transgenic mice.

Research projects

The role of TNF in CD8 T cell tolerance
Tumor Necrosis Factor (TNF) is a pleiotropic cytokine that plays a central role in inflammation and many autoimmune disorders. Recently we showed that TNF can have a direct effect on T cell responses to antigen. As a consequence,TNF ablation led to impaired CD8 T cell tolerance, at least in the cellular level. The genetic tools we used were mice transgenic for a specific TCR (F5 TCR) and mice expressing antigen recognized by F5 TCR (NP antigen). The impact of TNF was monitored by using TNF-deficient mice (TNF-/-).

Currently, we investigate the role of TNF in the pathophysiology of CD8 Tcell-mediated autoimmune diabetes in a mouse model. For that, we have recently generated a mouse model of autoimmune diabetes by directing expression of the antigen (NP) in ß pancreatic islets. The organ-specific expression of the antigen allows us to monitor events during encounter T cells with self-antigen and to better understand the contribution TNF:TNFR pathway in the autoimmune response.

The role of PD-1 in CD8 T cell tolerance
PD-1 (Programmed Death 1) has been identified as a homologue of CD28 and CTLA-4, and it is a receptor expressed on activated T cells containing an immunoreceptor tyrosine-based inhibitory motif and it functions as a negative regulator of immune responses. Initial studies in patients and experimental mouse models suggest an important role of the PD-1:PD-1L pathway in the pathogenesis of several autoimmune diseases.

We are proposing to introduce our autoimmune diabetes mouse model in a PD-1 deficient background. This will allow us to investigate the role of the negative costimulatory pathway PD-1: PD-1L on the establishment of peripheral T cell tolerance. This type of studies is necessary in order to investigate the possibility of engagement of this negative costimulatory pathway on T cells as a therapeutic intervention in transplant rejection and autoimmune disease.

The role of PD- 1 in T cell memory
T cell memory is an important component of the immune system. Defective differentiation and responses of memory T cells are related to decreased resistance to infections, cancer and coreelated to autoimmune disorders

We aim to decipher the role of negative costimulatory molecule PD- 1 in the differentiation of naïve to memory T cells and specifically the mechanisms underlying perturbed ratios of T cell memory subsets in the absence of PD-1 . We use protocols for inducing and monitoring T cell memory in wild- type and PD-1 deficient T cells. After characterization of these memory T cells we will identify specific molecules, pathways and cells responsible for the observed phenotype.

The role of TNF in homeostasis of naïve CD8 T cells
Recently, we have demonstrated that endogenous TNF plays a positive role in the survival of mature CD8 T cells, as well as in their homeostatic expansion under lymphopenic conditions.

We aim to investigate how TNF mutation affects the representation of T cell clones in the T cell pool. Moreover, we are interested in deciphering pathways downstream of TNF that affect T cell survival, by expression profile analysis.

Development of in vivo imaging technologies
To develop novel tools for monitoring T cells in vivo we are participating in the FP6 funded Integrated Project ”Integrated Technologies for In-Vivo Molecular Imaging”. In collaboration with the Institute of Electronic Structure and Laser –FORTH we are applying Fluorescent-mediated Molecular Imaging techniques to follow in-vivo fluorescently labeled cells. This will allow the study of interactions and preferential migration and distribution of cells within the immune system and their behavior during the immune response.

Thymus monitor in GFP-expressing neonates

Monitoring the Lymph node colonization