Mast cells in the liver

Mast Cells in Immune-Mediated Cholangitis and Cholangiocarcinoma

Cholestasis, which is impaired bile flow from the liver into the intestine, can be caused by cholangitis and/or bile duct obstruction. Cholangitis can arise from bacterial infections and cholelithiasis, however, immune-mediated cholangitis in primary biliary cholangitis (PBC) and primary sclerosing cholangitis (PSC) is characterized by a strong immune response targeting the biliary epithelial cells (BECs). Persistent biliary inflammation further represents a risk for biliary neoplasia, cholangiocarcinoma (CCA) by driving chronic cellular stress in the BECs. Currently, immune-mediated cholangitis is considered a Th1-Th17-dominant disease, however, the presence of Th2-related mast cells (MCs) in tissue samples from PBC, PSC and CCA patients has been described, showing that these MCs are active players in these diseases. Here, we reviewed and discussed experimental and clinical data supporting a pro-fibrotic role for MCs in immune-mediated cholangitis as well as their participation in supporting tumor growth acting as angiogenesis promoters. Thus, although MCs have classically been identified as downstream effectors of Th2 responses in allergies and parasitic infections, evidence suggests that these MCs are relevant players in biliary inflammation and neoplasia. The availability of strategies to prevent MCs’ activation represents a therapeutic opportunity in biliary diseases.

The anti-fibrotic role of mast cells in the liver is mediated by HLA-G and interaction with hepatic stellate cells

BACKGROUND & AIMS

We have reported a significant association between HLA-G expression or the number of hepatic mast cells and liver fibrosis. Here, we investigated the role of HLA-G and mast cells in liver fibrosis, focusing, in particular, on interactions between human mast and stellate cells.

METHODS

Human mast cells (HMC cell line, CD34-derived mast cells, or tissue-derived mast cells) were co-cultured with purified human hepatic stellate cells (HSCs), and collagen I production by HSCs was evaluated. Mast cells and HSCs were characterized by immunocytochemistry. Various conditions were tested: different times in direct or indirect contact, presence or absence of cytokines, addition or not of HLA-G, and presence or absence of specific protease inhibitors.

RESULTS

The reciprocal interaction between HSCs and mast cells led to the attraction of mast cells to HSCs in vivo and in vitro, and to a significant decrease in collagen production, at all times of co-culture, following the direct or indirect contact of mast cells with HSCs alone or in the presence of TGF-β, IFN-α or IL-10. We identified the diffusible factors involved in collagen I degradation as mast cell proteases. Moreover, HLA-G expression increased during the co-culture of HSCs and mast cells, with HLA-G acting on both mast cells and HSCs, to enhance collagen I degradation.

CONCLUSIONS

Mast cells play a beneficial, anti-fibrotic role in liver fibrosis, via the HLA-G-mediated decrease of collagen I. These findings are consistent with high levels of cross-communication between mast cells and hepatic stellate cells and the role of HLA-G.

The antifibrogenic effect of etanercept on development of liver cirrhosis induced by thioacetamide in rats

Liver cirrhosis is an elevating cause of morbidity and mortality worldwide. TNF-α/TNF-R1 signal is implicated in progression of many liver diseases. This study provides histological and ultrastructural view that clarifies the effect of etanercept, a TNF-α inhibitor, on development of thioacetamide (TAA)-induced liver cirrhosis and the accompanied hemosiderosis in rats, highlighting the implication and distribution pattern of hepatic TNF-R1. Sixty male albino rats (Rattus norvegicus) were equally randomized into three groups. Group I served as the control. Liver cirrhosis was triggered in the other two groups by intraperitoneal injection of TAA twice a week for five months. Group II received TAA only, while group III subcutaneously injected with etanercept one hour before TAA, along five months. At the end of the experiment, blood was collected for biochemical analysis and livers were excised for histological, immunohistochemical, and electron microscopical preparations. Rats treated with TAA only developed hepatic cirrhosis accompanied by massive deposition of hemosiderin; strong and widespread expression of hepatic TNF-R1 in sinusoidal endothelial cells (SECs), Kupffer cells (KCs), and many hepatocytes; and frequent appearance of fibrogenic, plasma, and mast cells, at the ultrastructural level. By contrast, administration of etanercept diminished the expression of TNF-R1, attenuated the accumulation of collagen and hemosiderin, and preserved the hepatic histoarchitecture. In conclusion, TNF-α signal via TNF-R1 may be implicated in the mechanism of fibrogenesis and the associated hemosiderosis. Etanercept may provide a promising therapeutic approach not only for attenuating the progression of fibrogenesis, but also for hepatic iron overload-associated disorders.

Spontaneous extracutaneous systemic mastocytosis in a cynomolgus macaque (Macaca fascicularis)

A uniform cell population of proliferating mast cells with poor cytoplasmic granularity and a few eosinophilic infiltrates was observed in hepatic portal tracts and the cecal submucosa of an adult male cynomolgus macaque (Macaca fascicularis) that was part of a drug safety assessment toxicity study. The proliferating mast cells were positive for Giemsa and toluidine blue staining and had strong immunoreactivity for mast cell tryptase and CD68. Considering size, morphology, immunoreactivity, and distribution of the lesions a benign proliferative disorder of connective tissue mast cells was diagnosed comparable to that seen in indolent systemic mastocytosis in humans, but lacking associated skin lesions. The finding of visceral mast cell proliferation has to be included in the spontaneous background pathology spectrum of cynomolgus macaques used in toxicological studies.

Association of mast cells and liver allograft rejection

MCs are important effector cells in a broad range of immune responses. Their role in liver allograft rejection is not clear. Twenty-one liver transplant recipients (mean age +/- s.d.; 10.2 +/- 4.1 yr) who experienced a rejection episode are included in this study. Biopsy specimens from normal livers (allograft biopsy with normal histopathology n = 5 and naive livers n = 6), transplanted livers with CR (n = 5), and transplanted livers with ACR (n = 26) were studied. The total number of PT in each biopsy specimen was documented, and the number of PT that contained MCs was expressed as a percentage of the total number of PT. MCs, percentage of PT containing MCs and the average number of MCs/PT was significantly higher in rejection specimens than in control biopsy samples. All parameters were significantly higher in CR group than AR groups. Increasing grades of rejection was also associated with progressively more MCs and MC/PT (r = 0.68 p = 0.000; r = 0.58 p = 0.002). Only serum bilirubin level was related to the MCs in AR group. Only MC/PT was detected as an independent predictor of graft survival (p = 0.011, RR 2.87 95% CI 1.3-6.5). Despite the fact that the role of MCs in liver allograft rejection is still unknown; they exist in inflammatory infiltrates during pediatric liver allograft rejection. MC-rich portal infiltrates may distinguish chronic liver rejection from other inflammatory states such as AR, hepatitis and biliary obstruction.

The complex functions of mast cells in chronic human liver diseases

Mast cells (MCs) are multifunctional effector cells of the immune system. MCs were originally thought to be involved in IgE-associated immediate hypersensitivity and allergic disorders, but it is now known that they contain or elaborate an array of mediators with a multitude of effects on many other cells. A number of studies have found that MCs are involved in various liver diseases. Although still controversial, they seem to be involved in the liver's fibrotic response to chronic inflammation and parasitic infection. Hepatic fibrosis is the most frequent liver response to toxic, infectious, or metabolic agents. During the establishment of this pathological condition, there is an increase in the components of the basement membrane that leads to continuous basement membrane-like structures being raised within Disse's space and a decrease in the number of sinusoid endothelial fenestrae. This leads to a complex process called "sinusoidal capillarization." At the cellular level, liver fibrogenesis is initiated by hepatocyte necrosis, which induces the recruitment of a large number of inflammatory cells, including MCs, which can be considered the primary effectors of the process changing sinusoidal endothelial cells into capillary-type endothelial cells. We review the roles played by MCs in hepatic chronic diseases and describe a biopsy section of hepatic tissue taken from a patient with chronic C virus-related hepatitis showing diffuse sinusoidal capillarization and a high density of MCs. This observation has led us to hypothesize a relationship between these highly specialized cells and sinusoidal capillarization.

Mast cell density, hepatic stellate cell activation and TGF-beta1 transcripts in the aging Sprague-Dawley rat during early acute liver injury

Mast cells (MCs) have been indicated as a source of various inflammatory cytokines, chemokines and growth factors. This study evaluates liver tissue MC density as a quantitative marker of acute liver inflammation in 2- and 19-month old rats treated with carbon tetrachloride (CCl4) toassess the relationships between MC density, hepatocellular damage, mRNA encoding TGF-beta1, hepatic stellate cell (HSC) activation and collagen levels. Consecutive histological sections from each age group were stained with toluidine blue to identify granulated MCs, Direct Red 80 to recognize collagen matrix, and by immunohistochemistry to identify activated hepatic stellate cells (HSCs), which were subsequently counted by means of a computer-aided image analysis. Histology showed hepatocellular necrosis with inflammatory cell infiltration and collagen matrix deposition. Two and 24 hours after intoxication, MC density had considerably increased in the younger rats, but less in those aged 19 months. Although the untreated older rats had a larger area occupied by activated HSCs than the untreated younger rats, the increase in the number of HSCs was greater in the younger rats both two and 24 hours after intoxication. The greater MC density in younger rats suggests that older rats have a reduced immune response or recruit fewer MCs. The activated HSCs and TGF-beta1 transcripts did not increase significantly during the study period, thus indicating that these are later events in chemically induced hepatic toxicity. In conclusion. MC density may be an index of acute liver inflammation after CCl4 intoxication.

Regulation of hepatic stellate cell proliferation and collagen synthesis by proteinase-activated receptors

BACKGROUND/AIMS

Thrombin and MC tryptase, which are agonists for proteinase-activated receptors-1 and -2, respectively, are both increased in injured liver. We have examined if rat stellate cells express these receptors and if receptor agonists influence stellate cell activation.

METHODS

Expression of mRNA for proteinase activated receptors-1 and -2 were examined by RT-PCR and Northern blotting in lysates of cultured stellate cells and receptor protein examined by Western blotting. The effects of receptor agonists on cell proliferation and collagen synthesis were examined by 3H-thymidine and 3H-proline incorporation assays, respectively.

RESULTS

Rat stellate cells activated by culture on plastic showed a progressive increase in expression of proteinase-activated receptor-1 and -2 mRNA and proteinase-activated receptor-2 protein as they transformed to a myofibroblastic phenotype. Proteinase-activated receptor-1 agonists thrombin and the peptide SFFLRN, and proteinase-activated receptor-2 agonists tryptase and the peptide SLIGRL induced stellate cell proliferation and the rapid phosphorylation of 44 and 42 kDa mitogen-activated protein kinases. PD98059, an inhibitor of these kinases, inhibited this proliferative response. Both tryptase and SLIGRL increased collagen secretion by stellate cells.

CONCLUSIONS

This study indicates that the natural proteinase-activated receptor agonists thrombin and MC tryptase might sustain liver fibrosis by promoting stellate cell proliferation and collagen synthesis.

Mast cell hyperplasia in chronic rejection after liver transplantation

The pathogenesis of chronic hepatic allograft rejection is poorly understood. Recent studies suggested that hepatic mast cells may be involved in the pathogenesis of chronic cholestatic liver disease. Because chronic rejection after liver transplantation is predominantly a cholestatic process, the aim of this study is to determine whether hepatic mast cells are involved in its pathogenesis. Biopsy specimens from (1) normal livers (n = 5), (2) transplanted livers with end-stage chronic rejection (n = 8), and (3) transplanted livers with acute cellular rejection (mild, n = 7; moderate, n = 5; severe, n = 7) were studied. Biopsy specimens were stained immunohistochemically for mast cells with human antitryptase antibody. Mast cell density was significantly increased in the chronic-rejection group (4.9 +/- 0.6/mm2) compared with controls (2.9 +/- 0.5/mm2; P <.05). The percentage of portal tracts containing mast cells was significantly greater in chronic-rejection (89% +/- 8%) than control biopsy specimens (69% +/- 5%; P <.05), as was the average number of mast cells per portal tract (5.4 +/- 0.9 v 1.9 +/- 0.4 cells; P <.01). In chronic rejection, tissue mast cells frequently were seen surrounding damaged bile ducts in inflamed portal tracts. Neither mast cell density nor distribution was significantly different from controls in posttransplantation biopsy specimens with acute cellular rejection of mild, moderate, or severe degree. The finding of mast cells infiltrating portal tracts and surrounding damaged bile ducts in chronic rejection suggests that hepatic mast cells may be important effector cells in the pathogenesis of chronic rejection.