Naturally occurring T regulatory cells control airway hyperresponsiveness

National Jewish Health, Denver CO

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Abstract

ABSTRACT In susceptible individuals, asthma is a complex disease characterized by heightened responses to relatively innocuous antigens encountered via the respiratory tract. In a shift in thinking away from simple imbalances in Th2 and Th1 responses, there is increasing evidence for a protective role for regulatory T cells in allergic disease where they exhibit control over effector Th1 and Th2 cells. Naturally-occurring CD4+CD25+Foxp3+ regulatory cells (nTregs) isolated from the lungs of naive mice and transferred intratracheally into sensitized recipients prior to challenge suppress all aspects of lung allergic responses including airway hyperresponsiveness (AHR), airway eosinophilia, Th2 cytokine production, and goblet cell metaplasia. Conversely, depletion of these cells with anti-CD25 enhanced all of these responses. Our data indicate that the suppressive phenotype of nTregs is dependent on CD8-MHC I interactions and their production of IL-10 and TGF[unreadable]. We will define the role of these nTregs in regulating mast cell-dependent and -independent AHR and whether they are responsible for the tolerant state induced by repeated allergen challenge. Using biochemical tools, genetic manipulation and in vitro and in vivo approaches, we will define the underlying mechanisms whereby CD8-MHC I interactions signal and maintain Foxp3 expression and the suppressive phenotype. We will also define how, in the absence of interaction with CD8 in recipient mice, the nTregs demonstrate plasticity, converting to an enhancing phenotype through production of Th2 cytokines. Since signaling through the glucocorticoid inducible tumor necrosis factor receptor (GITR) attenuates the suppressive phenotype, we will delineate the counter-regulatory signals provided through Foxp3 and GITR and the interplay between these two defining events that appear to govern the fate (suppressive or enhancing phenotype) of nTregs. For the first time, these studies will identify the indispensable role and mechanism whereby Foxp3+nTreg control the development of lung allergic responses in sensitized hosts exposed to allergen challenge. Elucidation of the molecular basis for the functional activation of nTregs and the underlying mechanisms dictating nTreg-mediated suppression or nTreg conversion to an enhancing phenotype will form the basis for the control of their function in diseases such as asthma.