Hepatic immune regulation by stromal cells.

A metabolic organ, the liver also has a central role in tolerance induction. Stromal cells lining the hepatic sinusoids, such as liver sinusoidal endothelial cells (LSECs) and hepatic stellate cells (HSCs), are the first liver cells to encounter gut-derived and systemic antigens, thereby shaping local and systemic tolerance. Recent studies have demonstrated that stromal cells can modulate immune responses by antigen-dependent and independent mechanisms. Stromal cells interfere with the function of other antigen-presenting cells (APCs) and induce non-responsive T cells as well as regulatory T cells and myeloid-derived suppressor cells (MDSCs). The immunosuppressive microenvironment thus created provides a means to protect the liver from tissue damage. Such tolerized surroundings, however, can be exploited by certain pathogens, promoting persistent liver infections.