3F). Activation of hepatic MAIT cells by IL-12 and IL-18 upon bacterial infection We recently demonstrated that overnight bacterial activation of Madecassoside healthy PBMCs activated MAIT cells to produce IFN- directly via MR1 as well while indirectly via IL-12- and IL-18-dependent mechanisms [13]. ssRNA40. Mechanistically, ssRNA40 induced hepatic monocytes to produce IL-12 and IL-18 cytokines, which stimulated IFN- production by liver-resident CD161Bright MAIT and CD56Bright NK cells. We also shown that ssRNA40-mediated activation could happen in pathologic (HBV- or HCV-chronically infected) livers and that a related cytokine-mediated activation of intrahepatic cells could also be induced upon bacterial infection. Thus, we showed the liver immune cells can respond vigorously to specific pathogen-associated molecules. The selective production of IFN- by liver-resident cells could have restorative implications for the treatment of chronic liver infections. Introduction The liver is an essential organ at the center of carbohydrate, lipid and protein metabolisms. It is crucial for clearing toxins and pathogens that reach the circulatory compartment from your gut. The liver is also home to abundant populations of innate immune cells (monocytes, NK and NKT cells) whose local activation needs to be tuned in order to avoid severe liver damage with life-threatening effects [1], [2]. For these reasons, the immunological environment of the liver has been primarily associated with tolerogenic features: large quantity of immunosuppressive cytokines/ligands (e.g., IL-10 or PD-L1), tolerance to LPS activation and production of inhibitory enzymes (e.g., arginase) that can suppress immune reactions [3], [4]. The ability of pathogens like HBV, HCV and spp. Madecassoside to establish prolonged infections in the liver can be facilitated by such immunotolerant features. The hypo-responsiveness of liver-resident immune cells is, however, not complete and selective triggers are known to activate hepatic NK or CD56+ T cells: for example, liver-resident iNKT cells are activated in mice infected with Pie charts depict the average proportion of different subsets of lymphocytes, monocytes and dendritic cells found in the liver (n?=?6) and in the peripheral blood (n?=?7) of healthy donors. MeanSD total concentration of cytokines (IFN-, IFN-, TNF-, IL-1, IL-6, IL-17a and IL-10) in the supernatant after stimulation of purified lymphocytes isolated from the peripheral blood (n?=?5) and liver (n?=?9) with the indicated TLR agonist and anti-CD3/CD28-coupled beads. Unstimulated lymphocytes were used to determine the background levels and the background subtracted values are displayed. Background subtracted MeanSD concentrations of individual cytokines quantified in the Cdh15 supernatant of purified lymphocytes isolated from the peripheral blood (n?=?5) or liver (n?=?9) and stimulated with either TLR8, TLR7 or TLR4 agonist or anti-CD3/CD28-coupled beads. Heatmap shows the background subtracted mean concentrations of IFN- in the supernatants of blood (n?=?5) or liver- derived lymphocytes (n?=?9) stimulated with the indicated TLR agonist. * and ** indicates P 0.05 and P 0.01 respectively. Fig. 1B shows the total production of IFN-, IFN-, IL1, IL-6, IL-10, TNF- obtained in PBMCs of 5 healthy subjects and LDCs from Madecassoside 9 healthy Madecassoside liver donors (matched for age). The tested TLR agonists activated higher production of cytokines in PBMCs than LDCs with the single notable exception of the TLR8 agonist ssRNA40. Analysis of the single cytokines produced in ssRNA40-activated LDCs showed a very high quantity of IFN-, followed by TNF- and IL-1 (Fig. 1C). IFN- quantity produced by ssRNA40-activated LDCs (5000 pg/mL) was higher than the IFN- brought on by anti-CD3/CD28-coupled beads (3000 pg/mL) and by the other TLR agonists ( 500 pg/mL) (Fig. 1C and 1D). ssRNA40-activated LDCs also produced high quantities of IL-1 and TNF-, but the differences between LDCs and PBMCs were not as dramatic as that observed for IFN-: on average 27 occasions higher in LDCs than PBMCs (Fig. 1C and 1D). The TLR4 agonist LPS elicited also a high production of cytokines in LDCs (Fig. 1B). The pro-inflammatory IL-1, IL-6 and Madecassoside TNF- and the immunoregulatory IL-10 cytokines.