Portal Vein Endothelium Research Articles

Mechanical stress induced EndoMT in endothelial cells through PPARγ downregulation

Portal hypertension is a group of clinical syndromes induced by increased portal system pressure due to various etiologies including cirrhosis. When portal hypertension develops, the portal vein dilates and endothelial cells (ECs) in the portal vein are subjected to mechanical stretch. In this study, elastic silicone chambers were used to simulate the effects of mechanical stretch on ECs under portal hypertension. We found that mechanical stretch decreased PPARγ expression in ECs by blocking the PI3K/AKT/CREB signaling pathway or increasing NEDD4-mediated ubiquitination and degradation of PPARγ. Moreover, PPARγ downregulation triggered Endothelial-to-mesenchymal transition (EndoMT) in ECs under stretch by promoting Smad3 phosphorylation. The PPARγ agonist rosiglitazone mitigated stretch-induced EndoMT in vitro and alleviated EndoMT of the portal vein endothelium in cirrhotic rats.

SREBF2 triggers endoplasmic reticulum stress and Bax dysregulation to promote lipopolysaccharide-induced endothelial cell injury.

An increased lipopolysaccharide (LPS) level in patients with cirrhosis induced the dysregulation of sterol regulatory element-binding transcription factor 2 (SREBF2), which participated in the modulation of tumor inflammatory microenvironment. However, the role of SREBF2 in the LPS-induced injury of portal vein endothelium was scarcely reported. This study aimed to investigate the effects of SREBF2 on the LPS-induced injury to endothelial cells (ECs) in vitro and in vivo and explore the underlying mechanism. In this study, we found that LPS increased SREBF2 expression through activating the TLR4/JNK/c-Jun pathway and suppressed UBE2I-mediated SREBF2 sumoylation to enhance its transcriptional activity. The dysregulation of SREBF2 induced ER stress by increasing the intracellular cholesterol level and facilitated Bax expression to cause additional damage to LPS-induced ECs. As a potential intervention, miR590-3p negatively regulated SREBF2 expression and upregulated UBE2I expression by targeting TLR4, thus alleviating LPS-induced injury. These results suggest that LPS-induced SREBF2 triggered ER stress and promoted Bax expression to injure ECs, which was reversed by miR590-3p. The mechanisms of SREBF2 mediated LPS-induced endothelial injury of portal vein, which might be the therapeutic target for PVT development in cirrhosis patients. 1. LPS promoted SREBF2 expression by activating the TLR4/JNK/c-Jun pathway and suppressed UBE2I-mediated SREBF2 sumoylation to upregulate SREBF2 transcriptional activity 2. SREBF2-mediated ER stress and Bax expression involved in LPS-induced EC injury 3. miR590-3p decreased SREBF2 expression by targeting TLR4 and mitigated LPS-induced EC injury.

Functionalized cerium oxide nanoparticles mitigate the oxidative stress and pro-inflammatory activity associated to the portal vein endothelium of cirrhotic rats

Background and aimsThe occurrence of endothelial alterations in the liver and in the splanchnic vasculature of cirrhotic patients and experimental models of liver diseases has been demonstrated. However, the pathological role of the portal vein endothelium in this clinical context is scarcely studied and, therefore, deserves attention. In this context, we aimed to investigate whether pathological endothelial activation occurs in the portal vein of cirrhotic rats.MethodsCirrhosis was induced in wistar rats by CCl4 inhalation. We generated immortalized endothelial cells from the portal vein of control (CT-iPVEC) and cirrhotic rats (CH-iPVEC) by retroviral transduction of the SV40 T antigen. We assessed differential gene expression and intracellular reactive oxygen species (ROS) levels in iPVECs and in portal veins of control and cirrhotic rats. Finally, we assessed the therapeutic effectiveness of cerium oxide nanoparticles (CeO2NP) on reversing PVEC activation and macrophage polarization.ResultsCH-iPVECs overexpressed collagen-I, endothelin-1, TIMP-1, TIMP-2, IL-6 and PlGF genes. These results were consistent with the differential expression showed by whole portal veins from cirrhotic rats. In addition, CH-iPVECs showed a significant increase in intracellular ROS and the capacity of potentiating M1 polarization in macrophages. The treatment of CH-iPVECs with CeO2NPs blocked intracellular ROS formation and IL-6 and TIMP-2 gene overexpression. In agreement with the in vitro results, the chronic treatment of cirrhotic rats with CeO2NPs also resulted in the blockade of both ROS formation and IL-6 gene overexpression in whole portal veins.ConclusionsEndothelial cells from portal vein of cirrhotic rats depicted an abnormal phenotype characterized by a differential gene expression and the induction of M1 polarization in macrophages. We identified the excess of intracellular reactive oxygen species (ROS) as a major contributor to this altered phenotype. In addition, we demonstrated the utility of the nanomaterial cerium oxide as an effective antioxidant capable of reverse some of these pathological features associated with the portal vein in the cirrhosis condition.

Portal endothelial damage in cirrhosis

Introduction: Cirrhotic patients show a systemic heparin-like effect at thromboelastometric tracing during infection or bleeding. Endotoxemia, shear stress and inflammation may lead to endothelial damage and subsequent release of endogenous heparinoids by disruption of glycocalyx. The endothelium of portal vein could be persistently damaged by portal hypertension, and this could correlate with the high incidence of portal vein thrombosis in cirrhosis. Data regarding heparin-like effect in the portal venous system are lacking.

Ethnic variation in the incidence of biliary atresia correlates with the frequency of the most prevalent haplotype in its population

The cause of biliary atresia (BA) remains an enigma. However, an ethnic diversity in the incidence of BA is so unique that anthropological approach may provide some etiopathogenetic implications in the disease mechanism. We previously reported that an association of maternal microchimerism (MMc) in BA and a significant compatibility of HLA-A between the patient with BA and their mother. Across the 10 countries (Japan, South Korea, Taiwan, Philippines, New Zealand (Maori population), UK, France, Germany, Norway, and Sweden), we determined the frequency of the most prevalent HLA haplotypes of each country from Allele Frequency Database and found that it was significantly correlated with the incidence of BA of the respective country (p = 0.0126). This observation better fits the MMc theory as an etiopathogenesis, that is, maternal effector cells are likely to migrate into the fetus in a relatively homogenous population and may damage the developing bile duct structure and portal vein endothelium, depending on materno-fetal tolerance and immunity.

Positive C4d staining of the portal vein endothelium in the liver of patients with biliary atresia: a role of humoral immunity in ongoing liver fibrosis.

This study aimed to clarify the role of complement activation in fibrogenesis in BA. In total, 27 paraffin-embedded liver biopsy samples were immunohistochemically analyzed using C4d polyclonal antibody, vascular cell adhesion molecule-1 (VCAM-1), and CD45. The liver samples were obtained from 25 patients during Kasai operation, and two additional specimens were obtained from 2 patients by needle biopsy later at the time of liver function deterioration. The degree of liver fibrosis was histologically graded 1-3. Among the 25 samples, 9 showed C4d-positive immunostaining localized on the endothelia of a few portal veins in the portal tract. The degree of fibrosis was correlated with C4d staining (p=0.025). The age at Kasai operation correlated with the degree of fibrosis and the C4d positivity. Two needle biopsy samples were positive for C4d. Among 13 samples submitted for VCAM-1 staining, 2 negative samples were C4d negative and all positive C4d samples were VCAM-1 positive with CD45 mononuclear cell infiltration. These findings suggest that ongoing cirrhosis could be a result of progressive "vasculopathy" of the portal vein caused by humoral and cell-mediated immune interaction.

Superoxid dismutase activity in portal vein endothelium after partial liver resection

To investigate superoxide dismutase (SOD) activity in the portal vein endothelium and malondialdehyde acid (MDA) production in liver tissue of rats submitted to 70% hepatectomy. Twelve rats were distributed in two groups (hepatectomy and sham). Animals were sacrificed on post operative day 1 and portal vein, liver tissue and blood samples were collected. Portal vein SOD production was measured using lucigenin-amplified chemiluminescence assays. MDA measurement was used as an index of oxidative stress through the formation of TBARS (Thiobarbituric Acid Reactive Species). There was no difference in post operative bilirubin, AST, ALT levels between groups. DHL level was higher in the hepatectomy group (p=0.01). MDA production in the remnant liver tissue and endothelial portal vein SOD activity were also significantly (p<0.05) elevated in the hepatectomy group when compared to control group. There was no correlation between MDA and SOD activity. SOD activity, on the other hand, showed a positive correlation with LDH level (p=0.038) and MDA levels showed a positive correlation with AST and ALT levels (p<0.001). There is an increased production of malondialdehyde acid in liver tissue after partial hepatectomy and increased activity of superoxide dismutase in portal vein endothelium as well.

Acute portal vein thrombosis precipitated by indomethacin in a HCV-positive elderly patient

BackgroundAn increased risk of venous thromboembolism has been reported in patients treated with non-steroidal anti-inflammatory drugs (NSAIDs). We describe a case of acute portal vein thrombosis (PVT) in a hepatitis C virus (HCV)-positive elderly patient following administration of indomethacin.Case presentationA 79-year-old HCV-positive man was hospitalized for severe abdominal pain, nausea and vomiting, 15 days after starting indomethacin for back pain. Clinical signs and imaging evaluations disclosed a picture of PVT. Indomethacin was discontinued, and the patient was started on fondaparinux and antithrombin. He was discharged 15 days later due to improvement of his clinical conditions. Thirty days later, a follow-up ultrasound did not show appreciable signs of PVT. The time elapsing between the start of analgesic therapy and PVT onset suggests a role of indomethacin as the triggering agent. Indomethacin could have precipitated PVT by a combination of at least two detrimental mechanisms: 1) direct action on liver vascular endothelium by inhibition of prostacyclin biosynthesis; 2) damage to the intestinal mucosa, followed by inflammatory and pro-coagulant activation of portal endothelium upon exposure to bacterial endotoxins.ConclusionsThis case can be of interest to physicians, who should exert caution when prescribing NSAIDs for inflammatory pain in patients with background inflammatory dysfunctions of the portal vein endothelium.

Sinusoidal C4d deposits in liver allografts indicate an antibody-mediated response: Diagnostic considerations in the evaluation of liver allografts

There is a paucity of data concerning the correlation of complement component 4d (C4d) staining in liver allografts and antibody-mediated rejection. Data about the location and character of C4d deposits in native and allograft liver tissues are inconsistent. We performed C4d immunofluorescence (IF) on 141 fresh-frozen liver allograft biopsy samples and native livers, documented the pattern of C4d IF staining, and correlated the findings with the presence of donor-specific alloantibodies (DSAs). A linear/granular sinusoidal pattern of C4d IF was noted in 18 of 28 biopsy samples obtained after transplantation from patients with positive crossmatch and detectable donor-specific alloantibody (pos-XM/DSA) findings. None of the 59 tested biopsy samples from patients with negative crossmatch and detectable donor-specific alloantibody (neg-XM/DSA) findings were C4d-positive (P < 0.001). No significant association was found between pos-XM/DSA and C4d IF staining in other nonsinusoidal liver compartments. To compare the results of sinusoidal C4d staining with IF and 2 immunohistochemistry (IHC) techniques, C4d IHC was performed on 19 liver allograft biopsy samples in which a sinusoidal pattern of C4d IF had been noted. Sinusoidal C4d IHC findings were negative for 17 of the 19 biopsy samples; 2 showed weak and focal staining, and both patients had pos-XM/DSA findings. Portal vein endothelium staining was present in only 1 IF-stained biopsy sample (pos-XM/DSA) but in 11 IHC-stained biopsy samples (2 of the 11 samples had neg-XM/DSA findings). We conclude that sinusoidal C4d deposits detected by IF in frozen tissue samples from liver allograft recipients correlate with the presence of DSAs and an antibody-mediated alloresponse. These observations are similar to findings reported for other solid organ transplants and can provide relevant information for patient management. Further validation of IHC techniques for C4d detection in liver allograft tissue is required.

Acute Myeloid Leukemia Cells Generate Leukemic Endothelial Cells with Leukemogenic Potential: Blood Vessels As Sanctuaries for Leukemia Relapse

Abstract 241Human hematopoietic stem cells (HSCs) possess hemangioblast activity, which is defined as the ability to generate both blood and endothelium. Whether malignant HSC counterparts such as acute myeloid leukemia (AML) also display this bipotentiality remains to be defined. To test the hemangioblast potential of AML cells we first cultured primary human AML bone marrow in conditions established by Yoder and colleagues that support the growth of functional endothelial cell (EC) progenitors. AML cultured in endothelial colony forming cell (ECFC) media generated endothelial progenitor cell colonies that showed uptake of acetylated LDL and expressed several EC surface proteins, including CD105, CD146, UEA-1 and CD144. Importantly, ECFCs derived from AML bone marrow no longer expressed CD45 or myeloid surface proteins such as CD14. When placed in Matrigel, these AML derived ECFC generated capillary-like, tubular structures. Moreover, these ECFCs contained cytogenetic mutations associated with their parental leukemias. Thus, under the appropriate conditions, AML bone marrow cells can generate cells with an endothelial-like phenotype and harboring leukemia specific mutations that will be referred to as ‘L-ECFC.’ To functionally define leukemia hemangioblast activity, a xenograft model of AML was employed. Sublethally irradiated NOD/scid/IL2Rγ−/− (NSG) mice were transplanted with primary human AML cells and then sacrificed at 8–36 weeks after transplant. Significant accumulations of human AML cells were found in perivascular regions of the liver. Both tight coupling and bona fide cell fusion between AML and ECs was observed. AML derived EC that were integrated into portal vein endothelium showed induction of CD105 expression Follow-up AML xenotransplant experiments with BrdU labeling revealed almost four-fold fewer (6%) of the AML cells incorporated within blood vessels were BrdU+, as compared to AML cells not integrated in blood vessels (22%) (P=0.01). These results suggest that AML cell incorporation within the endovascular lining induces cell quiescence. Thus, leukemia-integrated ECs may be less susceptible to cell cycle active agents like cytarabine. Results from these experiments also raised the possibility that AML cells adopting an endothelial-like phenotype may serve as a reservoir for leukemic relapse. To test this hypothesis, we injected CD105+CD45- L-ECFC derived from AML patients into NSG mice. These L-ECFC generated colonies of human CD105+CD45- within spleens and bone marrow of recipient mice. We also found a distinct population of human CD45+CD19- cells comprising 5–10% of bone marrow cells. Leukemia-derived cells were confirmed by detection of cytogenetically mutant cells consistent with the parent leukemia (e.g., MLL duplications). In conclusion, this study demonstrates that AML cells can functionally generate leukemic ECs that become quiescent after incorporation in blood vessel networks and can re-emerge with a leukemogenic phenotype. Together, our results raise the strong possibility that AML cells exhibit functional hemangioblast activity and that vascular endothelium may serve as a clinically important sanctuary for occult leukemia. Our data also support endothelial cell targeting strategies as a means to eradicate AML. Disclosures:No relevant conflicts of interest to declare.

Pathology and pathogenesis of portal venopathy in idiopathic portal hypertension: Hints from systemic sclerosis

Idiopathic portal hypertension (IPH) is a non-cirrhotic presinuosidal portal hypertension of unknown etiology. Stenosis of smaller portal veins with portal fibrosis is a pathologic hallmark of IPH. Association of systemic sclerosis (SSc) with IPH is recognized, and similar pathologic features are reported in small portal tracts and skin of IPH and SSc, respectively. In addition, levels of transforming growth factor-beta (TGF-beta) and connective tissue growth factor are elevated in serum and in affected skin and portal tracts of these two diseases, suggesting that IPH share fibrogenetic mechanisms with SSc. Endothelial to mesenchymal transition (EndMT) of microvasculatures of skin could be responsible for dermal fibrosis in SSc. In IPH, EndMT of portal vein endothelium via TGF-beta/Smad activation may also be involved in small portal venpathy. In IPH, enhanced expression of pSmad2 in venous endothelium of smaller portal veins was associated with reduced CD34 expression. CD34 and S100A4, and CD34 and type I collagen were colocalized to portal vein endothelium in IPH. Such myofibroblastic phenotypes may be responsible for periportal-venous deposition of collagen and compressive portal venous obliteration. These small portal venous lesions may in turn lead to portal venous insufficiency followed by subcapsular atrophy in IPH.

Endothelial to Mesenchymal Transition via Transforming Growth Factor-β1/Smad Activation Is Associated with Portal Venous Stenosis in Idiopathic Portal Hypertension

Idiopathic portal hypertension (IPH) represents noncirrhotic portal hypertension of unknown etiology, mainly due to stenosis of peripheral portal veins. This study was performed to clarify the mechanism of portal venous stenosis in IPH from the viewpoint of the contribution of the endothelial to mesenchymal transition of the portal vein endothelium via transforming growth factor-beta1 (TGF-beta1)/Smad activation. In vitro experiments using human dermal microvascular endothelial cells demonstrated that TGF-beta1 induced myofibroblastic features in human dermal microvascular endothelial cells, including spindle cell morphology, reduction of CD34 expression, and induction of S100A4, alpha-smooth muscle actin, and COL1A1 expression, as well as the increased nuclear expression of phospho-Smad2. Bone morphogenic protein-7 preserved the endothelial phenotype of human dermal microvascular endothelial cells. Immunohistochemical analysis showed that endothelial cells of the peripheral portal veins in IPH were characterized by the decreased expression of CD34 and the enhanced nuclear expression of phospho-Smad2; these results also confirmed the expression of S100A4 and COL1A1 in the portal vein endothelium. Serum TGF-beta1 levels in patients with IPH were significantly higher than those of healthy volunteers and patients with chronic viral hepatitis/liver cirrhosis, while an elevation of serum bone morphogenic protein-7 levels was not observed. These results suggest that the endothelial to mesenchymal transition of the portal venous endothelium via TGF-beta1/Smad activation is associated with portal venous stenosis in IPH, and bone morphogenic protein-7 may therefore be a suitable therapeutic candidate for IPH.

Progenitor Cell Characterization and Location in the Developing Human Liver

Tissue-derived stem cells may offer future liver disease therapies. The developing human liver provides an excellent model to examine normal hepatic progenitor cell maturation, but candidate populations are poorly characterized. We sought to identify putative progenitor phenotypes in first-trimester human liver, by characterizing the architectural relationship between developing epithelial, mesenchymal, and hematopoietic lineages. Bipotential hepatoblasts were identified by co-expression of hepatocytic (cytokeratin 18, albumin) and biliary(cytokeratin 19) specific markers and epithelial-specific E-cadherin. Restriction of dlk/pref-1 expression to hepatoblasts identifies this as a novel human marker allowing for hepatoblast sorting for in vitro analysis. Furthermore, the liver stem cell and haematopoietic marker Thy-1 was co-expressed with markers of hematopoietic (CD34) and mesenchymal (vimentin) lineage restriction on portal vein endothelium. Therefore, this structure may constitute a novel progenitor compartment with hemangioblast-like properties.

Effects of shear stress on [Ca2+]i and membrane potential of vascular endothelium of intact rat blood vessels

Shear stress is an important modulator of endothelial function which can affect vessel tone, endothelial morphology and gene transcription. However, the mechanism by which the endothelium detects changes in shear stress is the subject of conflicting reports. The possible contributions of changes in the cytosolic Ca2+ concentration ([Ca2+]i) and of membrane hyperpolarisation are disputed. Here we have investigated the effects of shear stress on these variables in native endothelium in situ in rat aorta and hepatic portal vein. Endothelial [Ca2+]i was recorded using the fluorescent indicator fura-2. The [Ca2+]i in unstimulated rat aortic endothelium was 86 ± 12 nM (n = 9). Acetylcholine (ACh) evoked relaxation of the aorta and a biphasic increase in endothelial [Ca2+]i. Shear stress that evoked relaxation comparable to that evoked by ACh did not affect the endothelial [Ca2+]i. Endothelial membrane potential was recorded using the patch clamp technique. The resting membrane potentials of rat aortic and portal vein endothelium were -47 ± 3.8 mV (n = 14) and -68 ± 4.5 mV (n = 9), respectively. Shear stress did not affect the endothelial membrane potential of rat aorta, but evoked a small (-1.6 ± 0.3 mV, n = 9) hyperpolarisation of the endothelium of rat portal vein in all preparations studied. These results suggest that neither changes in [Ca2+]i nor hyperpolarisation are involved in the reception of shear stress by native rat aortic endothelium in situ, but that shear stress induces small hyperpolarisations of endothelium of portal vein, a mechanism that may be present and of greater physiological significance in other parts of vascular system.

Effects of Shear Stress on [Ca2+]I and Membrane Potential of Vascular Endothelium of Intact Rat Blood Vessels

Shear stress is an important modulator of endothelial function which can affect vessel tone, endothelial morphology and gene transcription. However, the mechanism by which the endothelium detects changes in shear stress is the subject of conflicting reports. The possible contributions of changes in the cytosolic Ca2+ concentration ([Ca2+]i) and of membrane hyperpolarisation are disputed. Here we have investigated the effects of shear stress on these variables in native endothelium in situ in rat aorta and hepatic portal vein. Endothelial [Ca2+]i was recorded using the fluorescent indicator fura-2. The [Ca2+]i in unstimulated rat aortic endothelium was 86 +/- 12 nM (n = 9). Acetylcholine (ACh) evoked relaxation of the aorta and a biphasic increase in endothelial [Ca2+]i. Shear stress that evoked relaxation comparable to that evoked by ACh did not affect the endothelial [Ca2+]i. Endothelial membrane potential was recorded using the patch clamp technique. The resting membrane potentials of rat aortic and portal vein endothelium were -47 +/- 3.8 mV (n = 14) and -68 +/- 4.5 mV (n = 9), respectively. Shear stress did not affect the endothelial membrane potential of rat aorta, but evoked a small (-1.6 +/- 0.3 mV, n = 9) hyperpolarisation of the endothelium of rat portal vein in all preparations studied. These results suggest that neither changes in [Ca2+]i nor hyperpolarisation are involved in the reception of shear stress by native rat aortic endothelium in situ, but that shear stress induces small hyperpolarisations of endothelium of portal vein, a mechanism that may be present and of greater physiological significance in other parts of vascular system.

Role of intercellular adhesion molecule-1 and lymphocyte function-associated antigen-1 during nonsuppurative destructive cholangitis in a mouse graft-versus-host disease model.

Intercellular adhesion molecule-1 (ICAM-1) is expressed abnormally on the bile duct epithelium during the course of primary biliary cirrhosis (PBC), but the importance of ICAM-1 and its lymphocyte function-associated antigen-1 (LFA-1) receptor during the course of nonsuppurative destructive cholangitis (NSDC) has not been defined. To address this question, we defined the relationship between ICAM-1 on the intrahepatic bile duct epithelium and the evolution of NSDC lesions in a mouse graft-versus-host disease (GVHD) model. We also determined the effects of anti-ICAM-1 and anti-LFA-1 treatments on NSDC, intrahepatic lymphokine production, and the homing of lymphocytes to the livers of GVHD mice. ICAM-1 was initially detected on the bile duct epithelium and portal vein endothelium on day 7 of GVHD. There was a significant positive correlation between the intensity of ICAM-1 staining and histological bile duct damage (r =.58, P <.05) between day 3 and 28. Treatment with anti-ICAM-1 (but not anti-LFA-1) decreased both the mean grades of portal inflammation (P =.003) and NSDC (P =.002) lesions compared with control immunoglobulin G (IgG) treatments. Combined treatment with anti-ICAM-1 and anti-LFA-1 caused a further decrease in the amount of portal inflammation and bile duct damage compared with anti-ICAM-1, alone (P =.02). Anti-ICAM-1 treatment also decreased both the percentage of T cells and the production of interleukin-2 (IL-2) and IL-12 in the liver (P <.01), but had no effect on IL-4, IL-10, and interferon gamma. Neither anti-ICAM-1 nor anti-LFA-1 prevented lymphocytes from homing to the liver. These results indicate that both ICAM-1 and LFA-1 are important to the pathogenesis of NSDC.

Immunocytochemical analysis of HLA class II (DR) antigens in liver disease in man.

The in situ distribution of the major histocompatibility (HLA) class II (DR) antigens was studied in 113 liver biopsy specimens and five livers obtained at necropsy, using monoclonal antibody CR3/43. In 20 normal livers HLA-DR antigens were not detected in bile duct epithelium, hepatocytes, or portal vein endothelium. Normal arteriolar, sinusoidal and central venous endothelium often expressed HLA-DR. Kupffer cells always expressed these antigens. HLA-DR positive spindle cells were identified in the connective tissue of portal tracts, large hepatic veins, and liver capsule: most shared antigens common to all leucocytes and reacted with the histiocytic maker EBM11. Bile duct epithelium expresses HLA-DR in primary biliary cirrhosis, large duct obstruction, and drug induced cholestasis, indicating that HLA-DR positive spindle cells are phenotypically similar to histiocytes.

Mapping of the rat liver endothelial membrane with lectins and glycosylated ferritins.

We explored the luminal surface of liver sinus endothelium for the presence of lectin receptors and lectinlike substances capable of interacting with specific sugars. We used ferritin-conjugated lectins and glycosylated ferritins as probes. Incubation of small blocks of rat liver with these probes led to the binding of concanavalin A (on A), Ricinus communis (RCA), wheat germ agglutinin (WGA), phytohemagglutinin (PHA) and mannosyl ferritins to the luminal surface of endothelium. Ulex europaeus agglutinin I (UEA), fucosyl, galactosyl, and chitobiosyl-ferritins did not bind. The binding was patchy and sparse in the case of Con A and mannosyl-ferritins but uniform for others. Binding density did not correlate with hemagglutinability of lectins, suggesting that the difference in the hemagglutinability of these lectins did not account for the difference in their binding densities. Bindings were all completely inhibited in the presence of excess specific sugar inhibitors, indicating the specificity of binding. The distribution of binding was segregated on the endothelial membrane, being heaviest on luminal pits. To define the functional significance of this segregated distribution, sinus endothelium was compared to portal-vein endothelium in which endothelial fenestrations are also seen; and these fenestrations as well as pits may be covered by a thin diaphragm. Of interest was the total absence of binding to the diaphragm. The significance of these findings is discussed.

Induction of DR/IA antigens in human liver allografts. An immunocytochemical and clinicopathologic analysis of twenty failed grafts.

Twenty failed human liver allograft specimens obtained at the time of retransplantation procedures were studied using a panel of monoclonal antibodies (T11, T4, T8, NK, B1, OKM1, OKM5, Ia, DR). A clinicopathologic analysis was used to distinguish between graft failures secondary to rejection (n = 10) and those due, at least in part, to other causes (n = 10). T lymphocytes constituted the major infiltrating cellular population in the liver in rejection cases, but significant numbers of B cells and monocytes/macrophages were present also. Following transplantation, but not before, the bile duct epithelium, as well as portal and central vein and hepatic artery endothelium expressed DR/Ia antigens. These structures are preferential targets of the rejection reaction. The selective destruction of bile ducts in livers undergoing rejection was manifested in these patients by striking elevations of serum gamma glutamyl transpeptidase (GGTP) activity, a marker of biliary epithelial damage. The induced expression of DR/Ia antigens on structures targeted for immune destruction may be an important event in the pathogenesis of liver allograft rejection.