The role of macrophages in the development of biliary injury in a lipopolysaccharide-aggravated hepatic ischaemia-reperfusion model.

INTRODUCTION: Endotoxins, in the form of lipopolysaccharides (LPS), are potent inducers of biliary injury. However the mechanism by which injury develops remains unclear. We hypothesized that hepatic macrophages are pivotal in the development of endotoxin-induced biliary injury and that no injury would occur in their absence. MATERIAL AND METHODS: Clodronate liposomes were used to deplete macrophages from the liver. Forty-eight rats were equally divided across six study groups: sham operation (sham), liposome treatment and sham operation (liposomes+sham), 1mg/kg LPS i.p. (LPS), liposome treatment and LPS administration (liposomes+LPS), hepatic ischaemia-reperfusion injury with LPS administration (IRI+LPS) and liposome treatment followed by IRI+LPS (liposomes+IRI+LPS). Following 6h of reperfusion, blood, bile, and liver tissue was collected for further analysis. Small bile duct injury was assessed, serum liver tests were performed and bile composition was evaluated. The permeability of the blood-biliary barrier (BBB) was assessed using intravenously administered horseradish peroxidase (HRP). RESULTS: The presence of hepatic macrophages was reduced by 90% in LPS and IRI+LPS groups pre-treated with clodronate liposomes (P<0.001). Severe small bile duct injury was not affected by macrophage depletion, and persisted in the liposomes+IRI+LPS group (50% of animals) and liposomes+LPS group (75% of animals). Likewise, BBB impairment persisted following macrophage depletion. LPS-induced elevation of the chemokine Mcp-1 in bile was not affected by macrophage depletion. CONCLUSIONS: Depletion of hepatic macrophages did not prevent development of biliary injury following LPS or LPS-enhanced IRI. Cholangiocyte activation rather than macrophage activation may underlie this injury. This article is part of a Special Issue entitled: Cholangiocytes in Health and Diseaseedited by Jesus Banales, Marco Marzioni, Nicholas LaRusso and Peter Jansen.

A cohort study in university students: investigation of risk factors for cytomegalovirus infection.

Little is known about the main routes of human cytomegalovirus (HCMV) transmission in young adult populations. This study investigated risk factors for HCMV transmission in young adults attending university over a 3-year period. Blood samples were tested for HCMV specific viral capsid antigen IgG by enzyme immunoassay. Being born in a developing country and having lived in Africa were associated with HCMV seropositivity at study onset. No risk factors were associated with HCMV seroconversion over the 3-year follow-up. In contrast to previous reports, sexual activity was not associated with HCMV seroprevalence or seroconversion.

Epstein-Barr virus, B cell lymphoproliferative disease, and SCID mice: modeling T cell immunotherapy in vivo.

Epstein-Barr virus (EBV)-associated post-transplant lymphoproliferative disease (PTLD) arises in up to 10% of organ transplant recipients and is fatal in ∼50% of cases. PTLD can be modeled in SCID mice using EBV+ve human B lymphoblastoid cell lines (BLCLs), and the current study investigated intraperitoneal (ip) inoculation of such animals in experiments which assessed the effect of EBV-specific cytotoxic T lymphocytes (CTLs) and cytokines on PTLD growth. Ip transfer of one dose of autologous CTLs, or CD8-enriched T cells, into ip BLCL-inoculated animals significantly delayed tumor development (P = 0.001) and prevented tumor formation in a significant proportion (40%) of mice (P = 0.001). A combination of interleukin (IL)2, 7, and 15 conditioning of CTLs prior to ip injection significantly delayed ip BLCL-derived tumor formation in vivo when compared to CTLs expanded in vitro using only IL2 (P = 0.04) and prevented tumor outgrowth in a significant proportion (60%) of mice (P = 0.02). Daily ip IL2 dosing of ip CTL-inoculated mice significantly delayed tumor development in vivo (P = 0.004) and prevented tumor outgrowth in a significant proportion (78%) of mice (P = 0.02) when compared to animals dosed with vehicle only. In SCID mice, autologous CTLs, and CD8-enriched T cells, have significant capacity to hinder development of PTLD-like tumors. Whilst studies are needed to delineate the role of cytokine conditioning and CD4-enriched T cells, the results suggest that IL2 plays a key role in supporting CTL funtion in vivo.

Tumour necrosis factor gene polymorphism: a predictive factor for the development of post-transplant lymphoproliferative disease.

BACKGROUND: Epstein-Barr virus-positive post-transplant lymphoproliferative disease (PTLD) is a potentially lethal complication of iatrogenic immunosupression after transplantation. Predicting the development of PTLD allowing early and effective intervention is therefore of importance. Polymorphisms within cytokine genes are implicated in susceptibility to, and progression of, disease however the published data are often conflicting. We undertook investigation of polymorphic alleles within cytokine genes in PTLD and non-PTLD transplant cohorts to determine risk factors for disease. METHODS: SSP-PCR was used to analyse single nucleotide polymorphism within tumour necrosis factor (TNF)-alpha, interleukin- 1, -6, -10 and lymphotoxin-alpha genes. The TNF-alpha levels were measured by standard enzyme-linked immuno-absorbant assay. RESULTS: We show an association between variant alleles within the TNF-alpha promoter (-1031C (P=0.005)); -863A (P=0.0001) and TNF receptor I promoter regions (-201T (P=0.02)); -1135C (P=0.03) with the development of PTLD. We also show an association with TNF-alpha promoter haplotypes with haplotype-3 significantly increased (P=0.0001) and haplotype-1 decreased (P=0.02) in PTLD patients compared to transplant controls. Furthermore, we show a significant increase (P=0.02) in the level of TNF-alpha in PTLD patient plasma (range 0-97.97 pg ml(-1)) compared to transplant controls (0-8.147 pg ml(-1)), with the highest levels found in individuals carrying the variant alleles. CONCLUSION: We suggest that genetic variation within TNF-alpha loci and the level of plasma cytokine could be used as a predictive risk factor for the development of PTLD.

Regulatory T cell activity in primary and persistent Epstein-Barr virus infection.

Regulatory T cells (T(reg)) provide a balance to immune T cell activation thereby protecting the body from pathogen-induced immunopathology. Several persistent viruses induce T(reg) that subvert protective immune mechanisms and promote viral persistence. Epstein-Barr virus (EBV) generally infects children subclinically and persists thereafter, but primary infection in early adulthood may cause immunopathological damage manifest as infectious mononucleosis. In this study the role of T(reg) was investigated in acute infectious mononucleosis and healthy EBV seropositive donors. The proportion of CD4(+)CD25(high) T cells in blood from infectious mononucleosis patients was significantly lower than in seropositive donors (P = 0.05). Using the FOXP3 marker for T(reg) the same frequency and extra-follicular distribution of T(reg) was noted in infectious mononucleosis and control tonsils. Regulatory cytokines, interleukin (IL)-10 and transforming growth factor (TGF)-beta, were significantly raised in infectious mononucleosis compared to seropositive donor plasma (P = 0.0001, P = 0.0004 respectively) although levels of IL-10 peaked earlier in infectious mononucleosis than TGF-beta. Previous studies identified EBV latent membrane protein (LMP)-1-induced T(reg) activity [Marshall et al. (2003): J Immunol 170:6183-6189; Marshall et al. (2007): Brit J Haematol 139:81-89], and in this study a significant reduction in interferon-gamma production was found from infectious mononucleosis but not seropositive donor lymphocytes after stimulation with a recall antigen when LMP-1 peptide PRG was added (P = 0.03). It is possible that T(reg) are important in controlling primary EBV infection to a subclinical level in most cases and that infectious mononucleosis represents a failure of this protective mechanism.

Patient-focused outcomes following detection in a hospital-based screening programme for C282Y haemochromatosis.

BACKGROUND: Haemochromatosis is a common genetic disease in populations of a northern European origin. However, there is uncertainty as to whether it is a condition that should be screened for. AIMS: To determine the proportion of persons, in a public hospital setting, who were homozygous for the C282Y mutation for hereditary haemochromatosis and the proportion of these persons who would benefit from therapeutic phlebotomy. METHODS: All persons who had blood submitted for pathology testing, had total iron-binding capacity and iron measured and transferrin saturation calculated, and where this result exceeded 40%, genotyping for the C282Y mutation was carried out. RESULTS: Of 18,779 patients screened, 887 (5.4%) were found to have transferrin saturation greater than 40%. Thirty-five of these were homozygous for the C282Y mutation. Fourteen were previously known to be affected and six of these were non-compliant with venesection. Venesection was commenced in 5 of the 21 newly diagnosed subjects. CONCLUSIONS: The proportion of detected subjects who commenced venesection was significant. Results suggest that clinical penetrance is higher in Australia than other countries and that even in the environment of a large tertiary teaching hospital, phenotypic screening identifies cases of hereditary haemochromatosis, which are likely to benefit from treatment.

Immunity, homing and efficacy of allogeneic adoptive immunotherapy for posttransplant lymphoproliferative disorders.

Adoptive immunotherapy using autologous Epstein-Barr virus (EBV)-specific cytotoxic T-lymphocytes (auto-CTL) can regress posttransplant lymphoproliferative disorders (PTLD). Widespread applicability of auto-CTL remains constrained. Generation is time-consuming, and auto-CTL cannot be established in patients treated with the B-cell depleting antibody rituximab. By contrast, pregenerated allogeneic CTL (allo-CTL) offers immediate accessibility. Allo-CTL has previously shown efficacy in "early" polyclonal- PTLD. We treated three patients with aggressive, advanced monoclonal-PTLD following solid-organ transplantation. All were refractory to at least three prior therapies. Despite HLA disparity, there was negligible toxicity, with early in vivo antiviral efficacy and reconstitution of EBV peptide-specific immunity. Two patients attained complete remission (CR). One remains in CR 17 months following therapy, coincident with persistence of donor-derived tumor targeted EBV-specific CTL; the other died of non-PTLD related pathology. In the third patient, autopsy demonstrated homing of allo-CTL at the tumor site. Larger prospective studies of EBV-specific allo-CTL in PTLD are warranted.

Duodenal expression of iron transport molecules in untreated haemochromatosis subjects.

BACKGROUND AND AIMS: In HFE associated hereditary haemochromatosis, the duodenal enterocyte behaves as if iron deficient and previous reports have shown increased duodenal expression of divalent metal transporter 1 (DMT1) and iron regulated gene 1 (Ireg1) in affected subjects. In those studies, many patients had undergone venesection, which is a potent stimulus of iron absorption. Our study investigated duodenal expression of DMT1 (IRE and non-IRE), Ireg1, hephaestin, and duodenal cytochrome-b (Dyctb) in untreated C282Y homozygous haemochromatosis patients, iron deficient patients, and iron replete subjects. METHODS: Total RNA was extracted from duodenal biopsies and expression of the iron transport genes was assessed by ribonuclease protection assay. RESULTS: Expression of DMT1 (IRE) and Ireg1 was increased 3-5-fold in iron deficient subjects compared with iron replete subjects. Duodenal expression of DMT1 (IRE) and Ireg1 was similar in haemochromatosis patients and iron replete subjects but in haemochromatosis patients with elevated serum ferritin concentrations, both DMT1 (IRE) and Ireg1 expression were inappropriately increased relative to serum ferritin concentration. Hephaestin and Dcytb levels were not upregulated in haemochromatosis. DMT1 (IRE) and Ireg1 levels showed significant inverse correlations with serum ferritin concentration in each group of patients. CONCLUSIONS: These findings are consistent with DMT1 (IRE) and Ireg1 playing primary roles in the adaptive response to iron deficiency. Untreated haemochromatosis patients showed inappropriate increases in DMT1 (IRE) and Ireg1 expression for a given level of serum ferritin concentration, although the actual level of expression of these iron transport genes was not significantly different from that of normal subjects.

B lymphocytes in the normal brain: contrasts with HIV-associated lymphoid infiltrates and lymphomas.

In recent years evidence has accumulated which suggests that the brain may not be the immunologically privileged site it was once considered to be. It is now widely accepted that T lymphocytes perform surveillance functions in normal brain parenchyma. However, as yet there are no reports of B lymphocytes entering brain parenchyma in the healthy state. This study aimed to determine first the prevalence of B lymphocytes in normal brain, and subsequently whether advancing HIV infection led to changes in the brain B lymphocyte population, which might contribute to the increased risk of lymphoma seen in AIDS. Our results show that B lymphocytes do enter all parts of the normal human brain in very low numbers and that the B lymphocytes within the brain parenchyma display an activated (CD23 positive) phenotype. In contrast, intravascular B lymphocytes have a much lower expression of activation markers. B lymphocytes were found in increased numbers in both the brain parenchyma and perivascular spaces of pre-AIDS brains. However, brains from the majority of AIDS subjects, including those with primary CNS lymphoma (PCNSL) (outside the area of neoplastic involvement) contained fewer B lymphocytes than normal or pre-symptomatic HIV-infected brains. A subset of AIDS brains, previously shown to have pleomorphic lymphoid infiltrates in the perivascular spaces, had significantly increased numbers of B lymphocytes in both the brain parenchyma and perivascular spaces. Virtually all AIDS-related PCNSL are known to be Epstein-Barr Virus (EBV) positive, in contrast to non-HIV PCNSL and non-CNS AIDS-related lymphomas. We examined the EBV status of brain parenchymal B lymphocytes to investigate whether EBV-positive B lymphocytes are more frequent in HIV-infected brains than normal, thus explaining the propensity for CNS lymphomas in AIDS. In situ hybridization studies showed EBV positivity only in AIDS-related PCNSL cases within the lymphoma deposits. PCR-based studies detected high EBV copy numbers in PCNSL tumour tissue, and low copy numbers in AIDS cases with pleomorphic lymphoid infiltrates. As none of the B lymphocytes in this latter group were EBV positive on in situ hybridization, bearing in mind that this appears to be a prerequisite for PCNSL development, we find no evidence that pleomorphic infiltrates represent a pre-malignant PCNSL state.

Liver transplantation for HCV-associated liver cirrhosis: predictors of outcomes in a population with significant genotype 3 and 4 distribution.

End-stage liver disease associated with hepatitis C virus (HCV) infection is now the leading indication for liver transplantation in adults. However, reinfection of the graft is universal. We aimed to determine predictors of outcome of HCV-liver transplant recipients in the Australian and New Zealand communities. The following variables were analysed: demographic factors, coexistent pathology at the time of transplantation, HCV genotype, and donor age. Outcomes measures were: 1. mortality; 2. development of HCV-related complications, which were stage 3 or 4 fibrosis, or mortality from HCV-related graft failure, or both. Between January 1989 and December 30, 1999, 182 patients were transplanted for HCV-associated cirrhosis. The median follow-up period was 4 years (range, 0 to 13 years). Genotype data were available on 157 patients. The distribution of genotypes among the 157 patients was as follows: 36 (23%) genotype 1a, 30 (19%) genotype 1b, 4 (9%) genotype 1, 17 (11%) genotype 2, 41 (26%) genotype 3a, and 16 (10%) genotype 4. Eight (5%) patients were HCV-polymerase chain reaction (PCR)-negative (but HCV-antibody-positive). Donor age and genotype 4 were associated with an increased risk of retransplantation or death (P <.001 and.05, respectively). Meanwhile, donor age, genotype 4, and pretransplant excess alcohol were risk factors for the development of HCV-related complications (P =.004,.008, and.02, respectively). In contrast, patients with genotype 3a were less likely to develop HCV-related complications (P =.05). In a population of HCV liver transplant recipients with a heterogeneous genotype distribution, donor age, and genotype 4, were predictors of a worse outcome, whereas genotype 3 was associated with a more favorable outcome.

Predictions and associations of fatigue syndromes and mood disorders that occur after infectious mononucleosis.

BACKGROUND: Certain infections can trigger chronic fatigue syndromes (CFS) in a minority of people infected, but the reason is unknown. We describe some factors that predict or are associated with prolonged fatigue after infectious mononucleosis and contrast these factors with those that predicted mood disorders after the same infection. METHODS: We prospectively studied a cohort of 250 primary-care patients with infectious mononucleosis or ordinary upper-respiratory-tract infections until 6 months after clinical onset. We sought predictors of both acute and chronic fatigue syndromes and mood disorders from clinical, laboratory, and psychosocial measures. FINDINGS: An empirically defined fatigue syndrome 6 months after onset, which excluded comorbid psychiatric disorders, was most reliably predicted by a positive Monospot test at onset (odds ratio 2.1 [95% CI 1.4-3.3]) and lower physical fitness (0.35 [0.15-0.8]). Cervical lymphadenopathy and initial bed rest were associated with, or predicted, a fatigue syndrome up to 2 months after onset. By contrast, mood disorders were predicted by a premorbid psychiatric history (2.3 [1.4-3.9]), an emotional personality score (1.21 [1.11-1.35]), and social adversity (1.7 [1.0-2.9]). Definitions of CFS that included comorbid mood disorders were predicted by a mixture of those factors that predicted either the empirically defined fatigue syndrome or mood disorders. INTERPRETATION: The predictors of a prolonged fatigue syndrome after an infection differ with both definition and time, depending particularly on the presence or absence of comorbid mood disorders. The particular infection and its consequent immune reaction may have an early role, but physical deconditioning may also be important. By contrast, mood disorders are predicted by factors that predict mood disorders in general.

Complete regression of posttransplant lymphoproliferative disease using partially HLA-matched Epstein Barr virus-specific cytotoxic T cells.

BACKGROUND: Adoptive immunotherapy with autologous and donor-derived cytotoxic T lymphocytes (CTL) has recently been used to treat Epstein Barr virus (EBV)-positive posttransplant lymphoproliferative disease (PTLD). METHODS AND RESULTS: We report complete regression of EBV-positive PTLD in an 18-month-old small bowel and liver transplant recipient after one infusion of partially human leukocyte antigen (HLA)-matched EBV-specific CTL grown ex vivo from an EBV seropositive unrelated blood donor. No infusion-related toxicity or evidence of graft-versus-host disease was observed. The tumor showed signs of regression within 1 week and EBV load in peripheral blood dropped to undetectable levels. Limiting dilution analyses (LDA) detected no EBV-specific CTL precursor (CTLp) cells before the infusion, and high numbers of CTLp at 4 hr and 24 hr post-CTL infusion. There was a reversal of the CD4/8 ratio in peripheral blood and an increase in HLA-DR positive CD8 cells. The patient has been in complete remission for 24 months. CONCLUSION: If this success is repeated in more PTLD patients, then stored CTL could be used for antiviral and antitumor therapies in immunocompromised patients.

Lipid peroxidation in hepatic steatosis in humans is associated with hepatic fibrosis and occurs predominately in acinar zone 3.

BACKGROUND AND AIMS: Hepatic steatosis has been shown to be associated with lipid peroxidation and hepatic fibrosis in a variety of liver diseases including non-alcoholic fatty liver disease. However, the lobular distribution of lipid peroxidation associated with hepatic steatosis, and the influence of hepatic iron stores on this are unknown. The aim of this study was to assess the distribution of lipid peroxidation in association with these factors, and the relationship of this to the fibrogenic cascade. METHODS: Liver biopsies from 39 patients with varying degrees of hepatic steatosis were assessed for evidence of lipid peroxidation (malondialdehyde adducts), hepatic iron, inflammation, fibrosis, hepatic stellate cell activation (alpha-smooth muscle actin and TGF-beta expression) and collagen type I synthesis (procollagen alpha1 (I) mRNA). RESULTS: Lipid peroxidation occurred in and adjacent to fat-laden hepatocytes and was maximal in acinar zone 3. Fibrosis was associated with steatosis (P < 0.04), lipid peroxidation (P < 0.05) and hepatic iron stores (P < 0.02). Multivariate logistic regression analysis confirmed the association between steatosis and lipid peroxidation within zone 3 hepatocytes (P < 0.05), while for hepatic iron, lipid peroxidation was seen within sinusoidal cells (P < 0.05), particularly in zone 1 (P < 0.02). Steatosis was also associated with acinar inflammation (P < 0.005). alpha-Smooth muscle actin expression was present in association with both lipid peroxidation and fibrosis. Although the effects of steatosis and iron on lipid peroxidation and fibrosis were additive, there was no evidence of a specific synergistic interaction between them. CONCLUSIONS: These observations support a model where steatosis exerts an effect on fibrosis through lipid peroxidation, particularly in zone 3 hepatocytes.

Alcohol and the pancreas.

This article represents the proceedings of a workshop at the 2000 ISBRA Meeting in Yokohama, Japan. The presentations were (1) Phenotypic alteration of myofibroblast during ethanol-induced pancreatic injury: its relation to bFGF, by Masahiko Nakamura, Kanji Tsuchimoto, and Hiromasa Ishii; (2) Activation of pancreatic stellate cells in pancreatic fibrosis, by Paul S. Haber, Gregory W. Keogh, Minoti V. Apte, Corey S. Moran, Nancy L. Stewart, Darrell H.G. Crawford, Romano C. Pirola, Geoffrey W. McCaughan, Grant A. Ramm, and Jeremy S. Wilson; (3) Pancreatic blood flow and pancreatic enzyme secretion on acute ethanol infusion in anesthetized RAT, by H. Nishino, M. Kohno, R. Aizawa, and N. Tajima; (4) Genotype difference of alcohol-metabolizing enzymes in relation to chronic alcoholic pancreatitis between the alcoholic in the National Institute on Alcoholism and patients in other general hospitals in Japan, by K. Maruyama, H. Takahashi, S. Matsushita, K. Okuyama, A. Yokoyama, Y. Nakamura, K. Shirakura, and H. Ishii; and (5) Alcohol consumption and incidence of type 2 diabetes, by Katherine M. Conigrave, B. Frank Hu, Carlos A. Camargo Jr, Meir J. Stampfer, Walter C. Willett, and Eric B. Rimm.

Biology and disease associations of Epstein-Barr virus.

Epstein-Barr virus (EBV) is a human herpesvirus which infects almost all of the world's population subclinically during childhood and thereafter remains in the body for life. The virus colonizes antibody-producing (B) cells, which, as relatively long-lived resting cells, are an ideal site for long-term residence. Here EBV evades recognition and destruction by cytotoxic T cells. EBV is passed to naive hosts in saliva, but how the virus gains access to this route of transmission is not entirely clear. EBV carries a set of latent genes that, when expressed in resting B cells, induce cell proliferation and thereby increase the chances of successful virus colonization of the B-cell system during primary infection and the establishment of persistence. However, if this cell proliferation is not controlled, or if it is accompanied by additional genetic events within the infected cell, it can lead to malignancy. Thus EBV acts as a step in the evolution of an ever-increasing list of malignancies which are broadly of lymphoid or epithelial cell origin. In some of these, such as B-lymphoproliferative disease in the immunocompromised host, the role of the virus is central and well defined; in others, such as Burkitt's lymphoma, essential cofactors have been identified which act in concert with EBV in the evolution of the malignant clone. However, in several diseases in which the presence of EBV has more recently been discovered, the role of the virus is unclear. This review describes recent views on the EBV life cycle and its interlinks with normal B-cell biology, and discusses how this interrelationship may be upset and result in EBV-associated disease.

Role of myofibroblasts in tumour encapsulation of hepatocellular carcinoma in haemochromatosis.

BACKGROUND/AIMS: Hepatocellular carcinoma is a common malignancy and a major complication of untreated haemochromatosis. Encapsulation of liver tumours has been associated with a better prognosis and longer disease-free periods following resection. This study investigated the source of the tumour capsule in patients with haemochromatosis and coexisting hepatocellular carcinoma and examined potential factors influencing development. METHODS: Five haemochromatosis patients with encapsulated hepatocellular carcinoma were studied. Myofibroblasts were identified using combined immunohistochemistry and in situ hybridisation for alpha-smooth muscle actin and procollagen alpha1(I) mRNA, respectively. Immunohistochemistry was also performed for transforming growth factor (TGF)-beta1, platelet-derived growth factor (PDGF)-beta receptor and malondialdehyde. RESULTS: Procollagen alpha1(I) mRNA co-localised to alpha-smooth muscle actin positive myofibroblasts. The number of myofibroblasts was maximal within the capsule and decreased away from the tumour. TGF-beta1 protein was expressed in iron-loaded cells in non-tumour liver at the interface of tumour capsule. PDGF-beta receptor expression was observed in mesenchymal cells in the tumour capsule and in portal tracts. Malondialdehyde adducts were observed in the tumour, non-tumour tissue and in the capsule. CONCLUSIONS: This study provides evidence that myofibroblasts are the cell type responsible for collagen production within the tumour capsule surrounding hepatocellular carcinoma in haemochromatosis. The production of TGF-beta1 by iron-loaded hepatic cells at the tumour capsule interface may perpetuate the myofibroblastic phenotype, resulting in the formation of the tumour capsule.

Vitamin B12 and hepatitis C: molecular biology and human pathology.

Cobalamins are stored in high concentrations in the human liver and thus are available to participate in the regulation of hepatotropic virus functions. We show that cyanocobalamin (vitamin B12) inhibited the HCV internal ribosome entry site (IRES)-dependent translation of a reporter gene in vitro in a dose-dependent manner without significantly affecting the cap-dependent mechanism. Vitamin B12 failed to inhibit translation by IRES elements from encephalomyocarditis virus (EMCV) or classical swine fever virus (CSFV). We also demonstrate a relationship between the total cobalamin concentration in human sera and HCV viral load (a measure of viral replication in the host). The mean viral load was two orders of magnitude greater when the serum cobalamin concentration was above 200 pM (P < 0.003), suggesting that the total cobalamin concentration in an HCV-infected liver is biologically significant in HCV replication.