The molecular and cellular basis of complement-mediated T helper 1 (TH1) differentiation and regulation

A group of white cells called T lymphocytes forms a major part of our immune system and self-defence against dangerous infections. T lymphocytes seek and destroy pathogen-infected tissue and cells. However, these lymphocytes sometimes wrongly recognise proteins on our own tissues: This can cause destructive conditions such as rheumatoid arthritis and multiple sclerosis. Because T lymphocytes have such potent ability to be either beneficial or dangerous, their function is tightly regulated. To fight infections, these cells produce a cytokine called IFN-gamma. One of the control mechanisms to regulate the production of IFN-gamma is the induction of another cytokine, IL-10, within the same T cell, which then ?shuts down? IFN-gamm; expression. However, how exactly the T cell regulates the appropriate production of IFN-gamma vs. IL-10 is not understood. We have recently discovered that a protein called CD46 (which is present on the surface of T lymphocytes) is an important trigger for the switching of IFN-gamma to IL-10 in human T cells by sending appropriate signals into the cell. In addition, we have made the exciting observation that our finding is important for understanding a major human disease, rheumatoid arthritis (RA): We observed that the CD46 signals transduced do not work properly in T cells from RA patients (they do not shut down IFN-gamma). We now aim at finding out what exactly happens on a molecular level inside the cells when CD46 is activated on the cell surface of a healthy T cell. Understanding these ?signaling events? within healthy T cells will then allow us to compare those to data to signals from RA patients? T cells and define exactly were things ?are going wrong?. The understanding of this induction pathway will then lay the groundwork to understand the pathogenesis of RA and thereby to develop better diagnostics and therapies. The main investigator (CK) of this study is a leading authority in the functions of CD46 and regulatory lymphocytes. She has recently relocated from the US to the MRC Centre for Transplantation at King?s College and will now collaborate with outstanding experts (AC) in the RA field and in cytokine regulation (PL) on this project. Because King?s emphasizes strongly the crosstalk between basic research and clinical/patient work, CK will be in a position to rapidly interpret the findings for patient benefit. The proposed funding will help establish this promising body of work in the UK.

Control of IFN-gamma-secreting CD4+ TH1 effector T cells is vital for the prevention of immunopathologies during and after infection and unwanted responses against self or innocuous antigens. IL-10 is a key cytokine mediating negative control of TH1 responses. Although IL-10 is produced by several cell types and, thus, many cells can ?extrinsically? suppress TH1 responses, a novel concept now suggests that the major TH1 suppression pathway may be represented by ?intrinsic? regulation: A negative feedback loop working via the timely coinduction of IL-10 in addition to IFN-gamma within TH1 cells. Although the importance of IFN-gamma to IL-10 switching is acknowledged, the molecular pathways regulating these two cytokines in TH1 cells are undefined.
We identified the complement regulator CD46 as key receptor in regulating IFN-gamma and IL-10 production in TH1 cells (Cardone et. al, Nature Immunology, 2010). We demonstrated that CD46 not only drives IFN-gamma production and effector function of human TH1 cells but also induces the switch to IL-10 secretion and into the regulatory phase in an IL-2-dependent fashion: In the presence of low IL-2 CD46 induces almost exclusively IFN-gamma+ effector TH1 cells while high environmental IL-2 then switches these cells from an IFN-gamma+/IL-10+ intermediate finally into IL-10+ T cells, with both of the latter populations being suppressive. Importantly, we showed that this CD46-mediated switch is defective in rheumatoid arthritis (RA) patients: T cells from these patients lack the IL-10+ cell subpopulation, produce up to 20 times more IFN-gamma compared to those from healthy individuals and never enter the regulatory phase. Thus, we hypothesize that CD46-transduced signals play a vital role in the induction and resolution of human TH1 responses and that disturbance in CD46 signals is associated with RA. This application aims now at delineating the molecular signals regulating IFN-gamma/IL-10 switching in human TH1 cells. We propose that each of the CD46/IL-2-mediated sequential phases in the TH1 cell ?life cycle? (IFN-gamma+, the IFN-gamma+/IL-10+ and IL-10+) are defined by the expression of specific genes and miRNAs as well as distinct changes in the chromatin environment. We will identify those changes and generate a comprehensive transcriptomic signature of each of the TH1 induction and regulation phases present in T cells from healthy donors (in comparison with T cells from RA patients). This ?molecular landscape? will then provide an experimental framework to identify single proteins and pathways required for IFN-gamma/IL-10 switching, and to uncover the defect(s) in TH1 regulation in RA.