**4.4 Stellate cells**

Hepatic Stellate cells (HSCs) are another subset with immune function. This relatively small population (5–10% of liver parenchymal cells) resides in the space of Disse and is primarily involved in the storage of retinoid droplets and vitamin A and regulation of blood flow in the sinusoids [32, 46, 47]. In the intact liver, they are quiescent cells. Once activated, they differentiate to myofibroblast and participate in hepatic fibrosis pathogenesis [48]. The second direction of their function is the immunosuppression. Study in animals and humans show that they are effective antigen presenting cells with tolerogenic capacity because of the expression of PD-L1, B7-H7 and Fas/Fas-L pathways [49–51]. When activated, HSCs induce myeloid derived suppressor cells and Foxp3+ regulatory T cells by production of retinoic acid [52] In addition, they produce a broad range of cytokines, like TGF-b, IL-6 etc., and are able to respond to them, thus actively participate in the immunemediated network in the liver [48].
