CX3CR1 modulates the anti-inflammatory activity of hepatic dendritic cells in response to acute liver injury.

The chemokine fractalkine (CX3CL1) and its receptor CX3CR1 are known to mediate leukocyte chemotaxis, adhesion and survival. In the liver, CX3CR1 is expressed on multiple cell types including monocytes and dendritic cells. However, the function of CX3CR1 on hepatic dendritic cells (HDCs) is still poorly understood. In this study, we investigated the role of CX3CR1 on mouse HDCs during homeostasis and following acute liver injury. At homeostasis, CX3CR1-expression was detected among CD11b+/CD103- type 2 myeloid HDCs (mHDCs) and these cells were characterized by the production of IL-10.   Mice treatment with the hepatotoxic agent CCl4 up-regulated liver IL-10 expression and stimulated the expansion of CX3CR1+ mHDCs which also showed a more mature phenotype. The absence of CX3CR1 in naïve CX3CR1gfp/gfp mice specifically reduced the CD11b+/IL-10+ mHDCs as compared to CX3CR1-proficient animals (CX3CR1+/gfp).  Following CCl4 poisoning, the liver recruitment and maturation of CD11b+ mHDCs was significantly attenuated in CX3CR1gfp/gfp mice. Furthermore, these mice suffered more severe hepatic injury and inflammation than CX3CR1+/gfp mice and showed a delated recovery from liver damage. Such a worsening of liver injury in CX3CR1gfp/gfp mice was associated with an impaired up-regulation of hepatic IL-10 expression and a lower number of IL-10 producing CD11b+ mHDCs. Consistently, IL-10 inactivation enhanced hepatic injury and inflammation in CX3CR1+/gfp mice receiving CCl4 Altogether, these data indicate a novel role of the CX3CL1/CX3CR1 axis in liver type 2 mHDC functions, pointing out the importance of CX3CR1 in promoting IL-10-mediated anti-inflammatory actions of HDCs.

Long term intravital multiphoton microscopy imaging of immune cells in healthy and diseased liver using CXCR6.Gfp reporter mice.

Liver inflammation as a response to injury is a highly dynamic process involving the infiltration of distinct subtypes of leukocytes including monocytes, neutrophils, T cell subsets, B cells, natural killer (NK) and NKT cells. Intravital microscopy of the liver for monitoring immune cell migration is particularly challenging due to the high requirements regarding sample preparation and fixation, optical resolution and long-term animal survival. Yet, the dynamics of inflammatory processes as well as cellular interaction studies could provide critical information to better understand the initiation, progression and regression of inflammatory liver disease. Therefore, a highly sensitive and reliable method was established to study migration and cell-cell-interactions of different immune cells in mouse liver over long periods (about 6 hr) by intravital two-photon laser scanning microscopy (TPLSM) in combination with intensive care monitoring. The method provided includes a gentle preparation and stable fixation of the liver with minimal perturbation of the organ; long term intravital imaging using multicolor multiphoton microscopy with virtually no photobleaching or phototoxic effects over a time period of up to 6 hr, allowing tracking of specific leukocyte subsets; and stable imaging conditions due to extensive monitoring of mouse vital parameters and stabilization of circulation, temperature and gas exchange. To investigate lymphocyte migration upon liver inflammation CXCR6.gfp knock-in mice were subjected to intravital liver imaging under baseline conditions and after acute and chronic liver damage induced by intraperitoneal injection(s) of carbon tetrachloride (CCl4). CXCR6 is a chemokine receptor expressed on lymphocytes, mainly on Natural Killer T (NKT)-, Natural Killer (NK)- and subsets of T lymphocytes such as CD4 T cells but also mucosal associated invariant (MAIT) T cells1. Following the migratory pattern and positioning of CXCR6.gfp+ immune cells allowed a detailed insight into their altered behavior upon liver injury and therefore their potential involvement in disease progression.

Liver inflammation abrogates immunological tolerance induced by Kupffer cells.

UNLABELLED: The liver is essential for inducing immunological tolerance toward harmless antigens to maintain immune system homeostasis. However, the precise cellular mechanisms of tolerance induction against particle-bound antigens, the role of the local hepatic microenvironment, and implications for therapeutic targets in immune-mediated diseases are currently unclear. In order to elucidate cellular mechanisms of tolerance induction in healthy and injured liver, we developed a novel in vivo system combining the systemic delivery of low-dose peptide antigens coupled to inert particles, immunological readouts, and sophisticated intravital multiphoton microscopy-based imaging of liver in mice. We show that liver resident macrophages, Kupffer cells (KCs), but not hepatic monocyte-derived macrophages or dendritic cells (DCs), are the central cellular scavenger for circulating particle-associated antigens in homeostasis. KC-associated antigen presentation induces CD4 T-cell arrest, expansion of naturally occurring Foxp3(+) CD25(+) interleukin-10-producing antigen-specific regulatory T cells (Tregs) and tolerogenic immunity. Particle-associated tolerance induction in the liver protected mice from kidney inflammation in T-cell-mediated glomerulonephritis, indicating therapeutic potential of targeting KC for immune-mediated extrahepatic disorders. Liver inflammation in two independent experimental models of chronic liver injury and fibrosis abrogated tolerance induction and led to an immunogenic reprogramming of antigen-specific CD4 T cells. In injured liver, infiltrating monocyte-derived macrophages largely augment the hepatic phagocyte compartment, resulting in antigen redistribution between myeloid cell populations and, simultaneously, KCs lose signature markers of their tolerogenic phenotype. CONCLUSIONS: Hepatic induction of tissue-protective immunological tolerance against particulate antigens is dependent on KCs as well as on a noninflamed liver microenvironment, thereby providing mechanistic explanations for the clinical observation of immune dysfunction and tolerance break in patients with advanced liver diseases.

Differential induction of Ly6G and Ly6C positive myeloid derived suppressor cells in chronic kidney and liver inflammation and fibrosis.

CD11b+Gr1+ myeloid derived suppressor cells (MDSC) are known to be very potent suppressors of T cell immunity and can be further stratified into granulocytic MDSC and monocytic MDSC in mice based on expression of Ly6G or Ly6C, respectively. Here, using these markers and functional assays, we aimed to identify whether MDSC are induced during chronic inflammation leading to fibrosis in both kidney and liver and whether additional markers could more specifically identify these MDSC subsets. In an adenine-induced model of kidney inflammation/fibrosis suppressive Ly6Gpos MDSC were induced. The suppressive function within the Ly6G+ MDSC population was exclusively present in IFNγRß expressing cells. In contrast, in chronic inflammation in the liver induced by bile duct ligation, suppressive capacity was exclusively present in the Ly6Cpos MDSC subset. Gene expression analyses confirmed the differential origins and regulation of those MDSC subsets. Additionally, depletion of MDSC in either kidney or liver fibrosis enhanced fibrosis markers, indicating a protective role for MDSC in organ fibrosis. Thus, our data demonstrate that during liver inflammation and kidney fibrosis MDSC with similar function arise bearing a distinct marker profile and arising from different cell populations.