Integrating Signals from the T-Cell Receptor and the Interleukin-2 Receptor

T cells orchestrate the adaptive immune response, making them targets for immunotherapy. Although immunosuppressive therapies prevent disease progression, they also leave patients susceptible to opportunistic infections. To identify novel drug targets, we established a logical model describing T-cell receptor (TCR) signaling. However, to have a model that is able to predict new therapeutic approaches, the current drug targets must be included. Therefore, as a next step we generated the interleukin-2 receptor (IL-2R) signaling network and developed a tool to merge logical models. For IL-2R signaling, we show that STAT activation is independent of both Src- and PI3-kinases, while ERK activation depends upon both kinases and additionally requires novel PKCs. In addition, our merged model correctly predicted TCR-induced STAT activation. The combined network also allows information transfer from one receptor to add detail to another, thereby predicting that LAT mediates JNK activation in IL-2R signaling. In summary, the merged model not only enables us to unravel potential cross-talk, but it also suggests new experimental designs and provides a critical step towards designing strategies to reprogram T cells

Network model of immune responses reveals key effectors to single and co-infection dynamics by a respiratory bacterium and a gastrointestinal helminth

Co-infections alter the host immune response but how the systemic and local processes at the site of infection interact is still unclear. The majority of studies on co-infections concentrate on one of the infecting species, an immune function or group of cells and often focus on the initial phase of the infection. Here, we used a combination of experiments and mathematical modelling to investigate the network of immune responses against single and co-infections with the respiratory bacterium Bordetella bronchiseptica and the gastrointestinal helminth Trichostrongylus retortaeformis. Our goal was to identify representative mediators and functions that could capture the essence of the host immune response as a whole, and to assess how their relative contribution dynamically changed over time and between single and co-infected individuals. Network-based discrete dynamic models of single infections were built using current knowledge of bacterial and helminth immunology; the two single infection models were combined into a co-infection model that was then verified by our empirical findings. Simulations showed that a T helper cell mediated antibody and neutrophil response led to phagocytosis and clearance of B. bronchiseptica from the lungs. This was consistent in single and co-infection with no significant delay induced by the helminth. In contrast, T. retortaeformis intensity decreased faster when co-infected with the bacterium. Simulations suggested that the robust recruitment of neutrophils in the co-infection, added to the activation of IgG and eosinophil driven reduction of larvae, which also played an important role in single infection, contributed to this fast clearance. Perturbation analysis of the models, through the knockout of individual nodes (immune cells), identified the cells critical to parasite persistence and clearance both in single and co-infections. Our integrated approach captured the within-host immuno-dynamics of bacteria-helminth infection and identified key components that can be crucial for explaining individual variability between single and co-infections in natural populations

A mathematical model of combined CD8 T cell costimulation by 4-1BB (CD137) and OX40 (CD134) receptors.

Combined agonist stimulation of the TNFR costimulatory receptors 4-1BB (CD137) and OX40(CD134) has been shown to generate supereffector CD8 T cells that clonally expand to greater levels, survive longer, and produce a greater quantity of cytokines compared to T cells stimulated with an agonist of either costimulatory receptor individually. In order to understand the mechanisms for this effect, we have created a mathematical model for the activation of the CD8 T cell intracellular signaling network by mono- or dual-costimulation. We show that supereffector status is generated via downstream interacting pathways that are activated upon engagement of both receptors, and in silico simulations of the model are supported by published experimental results. The model can thus be used to identify critical molecular targets of T cell dual-costimulation in the context of cancer immunotherapy

GATA3 induces mitochondrial biogenesis in primary human CD4+ T cells during DNA damage

GATA3 is as a lineage-specific transcription factor that drives the differentiation of CD4+ T helper 2 (Th2) cells, but is also involved in a variety of processes such as immune regulation, proliferation and maintenance in other T cell and non-T cell lineages. Here we show a mechanism utilised by CD4+ T cells to increase mitochondrial mass in response to DNA damage through the actions of GATA3 and AMPK. Activated AMPK increases expression of PPARG coactivator 1 alpha (PPARGC1A or PGC1α protein) at the level of transcription and GATA3 at the level of translation, while DNA damage enhances expression of nuclear factor erythroid 2-related factor 2 (NFE2L2 or NRF2). PGC1α, GATA3 and NRF2 complex together with the ATR to promote mitochondrial biogenesis. These findings extend the pleotropic interactions of GATA3 and highlight the potential for GATA3-targeted cell manipulation for intervention in CD4+ T cell viability and function after DNA damage

Akt and STAT5 mediate naïve human CD4+ T-cell early metabolic response to TCR stimulation

Metabolic pathways that regulate T-cell function show promise as therapeutic targets in diverse diseases. Here, we show that at rest cultured human effector memory and central memory CD4+ T-cells have elevated levels of glycolysis and oxidative phosphorylation (OXPHOS), in comparison to naïve T-cells. Despite having low resting metabolic rates, naive T-cells respond to TCR stimulation with robust and rapid increases in glycolysis and OXPHOS. This early metabolic switch requires Akt activity to support increased rates of glycolysis and STAT5 activity for amino acid biosynthesis and TCA cycle anaplerosis. Importantly, both STAT5 inhibition and disruption of TCA cycle anaplerosis are associated with reduced IL-2 production, demonstrating the functional importance of this early metabolic program. Our results define STAT5 as a key node in modulating the early metabolic program following activation in naive CD4+ T-cells and in turn provide greater understanding of how cellular metabolism shapes T-cell responses

Analysis of the TCR-mediated signaling dynamics

Magdeburg, Univ., Fak. für Naturwiss., Diss., 2014von Mateusz Pawel Poltora

The role of metabolism during T cell senescence

PhD ThesisThe impact of T cell senescence during ageing is well established. However, T cell senescence is now recognised to play a role in a variety of age-related and metabolic diseases, such as rheumatoid arthritis and cardiovascular disease. It is therefore crucial to gain a better understanding of the mechanisms that control T cell senescence. The loss of mitochondria has been linked to both cellular senescence and ageing; however, it is still unclear whether mitochondria play a causal role in T cell senescence. Data presented here provides evidence that the differing susceptibilities to senescence that exist between CD8+ and CD4+ T cells is due to the inherent differences in mitochondrial content and cellular metabolism. Notably CD4+ T cells displayed a higher mitochondrial mass, shown to be the result of a GATA3-PGC1a complex, which is recruited as a consequence of DNA damage. Additionally, this thesis demonstrates the existence of a novel naïve-like senescent T cell subset, highlighting the heterogeneity of senescent T cells. This subset was found to arise because of inflammation; therefore, senescent T cells isolated from people living with type 2 diabetes (T2D) were used as a model to examine the characteristics of this subset further. Inflammatory-derived senescent T cells were phenotypically distinct to those examined from healthy age-matched control donors. With T2D senescent T cells expressing fewer of the traditional senescent-associated T cell markers and retaining more proliferative capacity, indicating they were derived from a less differentiated T cell subset. Despite this, inflammatory-derived senescent T 4 cells exhibited more severe mitochondrial dysfunction and dysregulated nutrient uptake and usage. Collectively, this thesis highlights the heterogeneity of senescent T cells and supports the ever-growing appreciation that cellular metabolism and senescence are intimately linked. Going forward, mitochondrial health and cellular metabolism should be included to better define the senescence phenotype

Modelling microdomain-mediated protein sorting in immunological signalling

Compartmentalisation is a fundamental feature of biological systems. The organism as a whole can be seen as a single compartment of the wider ecosystem. At lower scales, we observe biological processes compartmentalised into organs, cells, cell subtypes and organelles. In the highly complex discipline of immunology, compartmentalisation is key in order to respond e ciently to foreign antigens and to maintain the balance between immunity and tolerance. Recent studies have raised questions about the role of compartmentalisation in lipid membranes, from the relatively well described immunological synapse, to the smaller, more transient lipid raft or microdomain. This thesis asks whether, and how, microdomains could in uence the formation of small receptor complexes. Speci cally, we approach what appears to be a simple surface reaction-di usion problem from multiple viewpoints: explicitly simulating particle di usion using a probabilistic pixel-based model, and deriving a deterministic relation between spatial parameters and the timecourse of chemical concentrations throughout the model space. We also show the equivalence between the predictions of these two models, further supporting the validity of our approach. We also embed the results of our model output in an existing model of the immunological response in order to determine the downstream consequences of enhanced receptor organisation. The study gives a broader understanding of the mechanisms involved in microdomain-mediated protein sorting, highlights the degree of interdependence on multiple spatial and chemical parameters and suggests numerous avenues for future research