"The overall goal of this project is to test, in the human system, several hypotheses related to the role of T helper (Th) subsets in immunity and immunopathology. Using an experimental approach that takes advantage of high throughput culture methods and combines the ex vivo analysis of memory T cells with the in vitro priming of naïve T cells, we will dissect the Th cell response to pathogens, allergens, and self-antigens, in terms of antigen-specificity, tissue tropism, and cytokine production. We will identify signals and pathways triggered by microbes and allergens that prime polarized Th1, Th2, Th17 and Th22 cells as well as T cells with hybrid phenotypes producing, for instance, IFN-γ and IL-17 or IL-4 and IL-22. We will also address fundamental questions related to tolerance and autoimmunity by measuring frequency and distribution of self-reactive T cells in healthy donors and patients. The analysis of the response to microbes and allergens will address the possibility that different antigens, depending on abundance or location, may drive divergent Th cell responses, thus shedding light on the mechanisms of polarization and immunodominance in vivo. In pilot studies the project will also translate basic findings to the clinical setting, linking polarized Th responses to disease state and severity. Finally, using lentiviral-based approaches for gene silencing and overexpression, we will perform mechanistic studies to understand how environmental factors modulate in Th cells the production of pro- and anti-inflammatory cytokines. The hypotheses tested are strongly supported by preliminary observations from our own laboratory as well as from the biomedical literature. We expect that these studies will significantly expand our basic understanding of T cell biology and will have translational implications for the definition of correlates of protection or disease activity and for the design of improved vaccination and therapeutic strategies."