The molecular basis of regulatory T cell recruitment to the inflamed liver

Immune system of body recognise and attack invading non-self antigen at the same time recongnize the self antigen. Most chronic liver diseases occur as a consequence of the recruitment from blood of white blood cells called T cells which are designed to fight infection but as a side-effect also cause tissue damage. In recent years a subset of T cells called regulatory cells (Treg) has been described which suppresses tissue damage caused by other T cells. These cells evolved to prevent collateral damage during immune responses to infections but recent evidence suggests they are important in chronic inflammation, transplant rejection, autoimmune diseases and tumor immune response. Consistent with this, I have detected increased numbers of Treg in patients with chronic inflammatory liver diseases. I hypothesise that particular Treg will be recruited to the liver during inflammation and that specific molecules will control this process. I plan to test this hypothesis using a combined approach in which the homing behaviour of these cells in studied in human systems in vitro as well as by transferring cells in vivo. These studies will be among the first to investigate how Treg are recruited form the blood into sites of liver inflammation and may suggest new treatments for inflammatory liver diseases in which the number of local Treg within the tissue is manipulated in favour of resolution of inflammation.

Autoimmune liver diseases develop due to breakdown in immunological tolerance of self-antigens. Suppression of self-reactive T cells by CD4+CD25+ regulatory T cells (Treg) is essential for self-tolerance but little is known about how these cells enter tissues. I have detected intrahepatic Treg in autoimmune liver disease and shown they express high levels of the chemokine receptor CXCR3 which we have shown to be involved in lymphocyte recruitment to the liver. I hypothesise that activation of Treg in hepatic lymphoid tissues results in the loss of lymph node homing receptors and the acquisition of CXCR3 and other receptors that promote entry to inflamed liver where they suppress inflammation. To test this hypothesis I will carry out the following studies
Study 1 The expression of homing receptors on intrahepatic Treg will be determined using confocal microscopy of liver tissue and detailed flow cytometry of Treg isolated from normal and inflamed liver tissue. Intrahepatic Treg will be compared with those isolated from lymph node and skin and regulatory function confirmed using allogeneic suppression assays.
Study 2 To determine how Treg enter liver tissue during recruitment from blood I will use tissue and cell-based adhesion assays to study Treg adhesion to human hepatic endothelium. I will inhibit the homing receptors defined in study 1 to determine which molecules are involved.
Study 3. Do different populations of Treg undergo tissue-specific homing in vivo? Although in vitro models will provide unique information about Treg recruitment via human hepatic endothelium I also need to investigate these processes in vivo. Adoptive transfer experiments in a murine hepatitis model will be used to compare tissue-specific homing of CD4+CD25- (non-regulatory) T cells with CD4+CD25high Treg. In addition by sorting Treg based on expression of CXCR3 and other homing receptors I will be able to determine which receptors specifically promote Treg recruitment to inflamed liver. Finally I will use intravital microscopy to determine the molecular interactions involved in Treg recruitment via the hepatic vasculature.
These studies will be the first to define the molecular regulation of Treg recruitment to the liver. In addition they may suggest strategies in which therapeutic Treg are generated with a tissue-homing phenotype for specific delivery to the liver in patients with autoimmune liver disease.