Human Liver Mononuclear Cells

Expression of KIRs in PB and Liver NK, NKT and T Cells

The immune response to pathogens, alloantigens, and tumors is typically studied in peripheral blood, with limited information on the mechanisms in peripheral tissues such as the liver. Liver-specific immune responses involve various non-parenchymal cells and liver-associated lymphocytes, which differ phenotypically and functionally from peripheral blood mononuclear cells (PBMCs). Podhorzer et al. leverages liver perfusion methodologies to obtain LMCs, aiming for an in-depth analysis of natural killer (NK) and T cells (NKT) subsets to advance researchers understanding of liver-specific immune responses and their roles in liver diseases.

They compared the expression of KIR genes across peripheral blood, liver eluates, and a few mononuclear cell samples from liver biopsies, focusing on different KIRs due to limited sample sizes. In PB, KIR gene expression followed the order: CD56^dim > NKT > CD56^bright > T cells. In the liver, the order was: CD56^dim > NKT > T > CD56^bright cells. In PB, CD56^bright NK cells had less than 10% KIR expression. However, CD56^bright NK cells from the liver showed increased KIR3DL2 and KIR2DL3. CD56^dim cells had higher KIR expression, with PB CD56^dim cells showing significant levels of KIR2DS4. Comparative analysis revealed higher KIR2DL3 and KIR2DS1 expression in liver NKT cells compared to PB. For T cells, liver T cells exhibited significantly increased KIR expression: KIR2DL3, KIR3DL2, KIR2DS1, KIR2DS3, and KIR2DS4. Trends toward significance were also observed for KIR2DL2/2DS2, highlighting that three of the elevated KIR genes in liver T cells are activators, with KIR2DS4 and the weaker inhibitor KIR2DL3 showing the highest expression levels.

Fig. 1. Gating strategy for analyzing KIR expression in peripheral blood and liver CD45+ cells: comparison of CD56^bright, CD56^dim, NKT, and T Cell populations (Podhorzer A, Machicote A, et al., 2018).

Innate Immunity Gene RNA Expression in Various Primary Liver Cells

The multifaceted liver not only processes metabolic information, detoxifies and digests food, it is also an important immune system. It contains the cell types that allow for sensing and targeting pathogens through a network of pattern recognition receptors (PRRs), including Toll-like receptors (TLRs) and RIG-I-like receptors. Faure-Dupuy et al. aimed to quantify expression and function of innate immune pathways in primary human liver cells for a better understanding of liver immune responses.

Primitive human liver hepatocytes (PHH), liver sinusoidal endothelial cells (LSEC), hepatic stellate cells (HSC) and Kupffer cells (KC) were isolated from several liver resections. On these unstimulated cells, baseline levels of 53 mRNAs involved in pathogen recognition and immune surveillance were identified via microfluidic high-throughput quantitative RT-qPCR. As controls, they used total peripheral blood mononuclear cells (PBMCs) and total nonparenchymal liver mononuclear cells (LMNCs) from different donors free of HBV, HCV and HIV. Comparatively, resident LMNCs exhibited higher gene expression levels at the basal state than PBMCs, highlighting the liver's crucial role in host immunity. Specifically, liver cells demonstrated elevated expression of several cytosolic DNA (DDX3, Ku70, DHX9, DHX36) and RNA sensors (RLR, RIG-I, MDA-5). TLR2 and TLR4 were notably elevated in KCs, while other TLRs had lower expression. Adaptors for TLR signaling (MyD88, TRIF, TRAM) and transcription factors (IRF1, 3, 7) had high basal expression. NOD1 and NOD2 were minimally detected, but their adaptor RIP2 was present. Inflammasome receptor mRNAs were low, though ASC and caspase 1 proteins were detectable.

Fig. 2. Liver cells expression of innate sensors and related molecules in PHH, LSEC, HSC, KC, LMNC, and PBMC (Faure-Dupuy S, Vegna S, et al., 2018).