Johannes Herkel

Identification of target antigen for SLA/LP autoantibodies in autoimmune hepatitis

BACKGROUND Autoantibodies are a hallmark of autoimmune hepatitis, but most are not disease specific. Autoantibodies to soluble liver antigen (SLA) and to liver and pancreas antigen (LP) have been described as disease specific, occurring in about 30% of all patients with autoimmune hepatitis, but no standardised assays are available. Methods We tested 2000 serum samples from patients with various liver diseases and controls for SLA autoantibodies by inhibition ELISA. Serum samples positive for SLA antibodies were used for immunoscreening of cDNA expression libraries. Identified clones were tested against a panel of serum samples positive for SLA and LP autoantibodies and control serum samples, and the epitope mapped by deletion mutants and exonuclease digestion. FINDINGS SLA and LP autoantibodies were identical. Of 2000 serum samples screened, 35 were positive for SLA autoantibodies. These positive samples came from patients with autoimmune hepatitis; three from patients with an overlap syndrome (primary biliary cirrhosis and secondary autoimmune hepatitis). Expression cloning and absorption experiments identified a 422 aminoacid protein present in two splice variants as the sole target antigen. Aminoacids 371-409 were critical for immune recognition. INTERPRETATION The identified cDNA encodes the primary target antigen of SLA/LP autoantibodies. The SLA/LP antigen has a previously unknown aminoacid sequence, and presumably codes for an unindentified enzyme, suggested to be UGA-suppressor tRNA-associated protein. SLA/LP autoantibodies are disease specific and recognise a dominant epitope, suggesting a specific antigen-driven immune response. Identification of the SLA/LP target antigen will allow establishment of a reliable, widely available diagnostic assay. Furthermore, its role in the pathogenesis of autoimmune hepatitis can now be studied.

Ectopic expression of neural autoantigen in mouse liver suppresses experimental autoimmune neuroinflammation by inducing antigen-specific Tregs

Tregs are important mediators of immune tolerance to self antigens, and it has been suggested that Treg inactivation may cause autoimmune disease. Therefore, immunotherapy approaches that aim to restore or expand autoantigen-specific Treg activity might be beneficial for the treatment of autoimmune disease. Here we report that Treg-mediated suppression of autoimmune disease can be achieved in vivo by taking advantage of the ability of the liver to promote immune tolerance. Expression of the neural autoantigen myelin basic protein (MBP) in the liver was accomplished stably in liver-specific MBP transgenic mice and transiently using gene transfer to liver cells in vivo. Such ectopic MBP expression induced protection from autoimmune neuroinflammation in a mouse model of multiple sclerosis. Protection from autoimmunity was mediated by MBP-specific CD4+CD25+Foxp3+ Tregs, as demonstrated by the ability of these cells to prevent disease when adoptively transferred into nontransgenic mice and to suppress conventional CD4+CD25- T cell proliferation after antigen-specific stimulation with MBP in vitro. The generation of MBP-specific CD4+CD25+Foxp3+ Tregs in vivo depended on expression of MBP in the liver, but not in skin, and occurred by TGF-beta-dependent peripheral conversion from conventional non-Tregs. Our findings indicate that autoantigen expression in the liver may generate autoantigen-specific Tregs. Thus, targeting of autoantigens to hepatocytes may be a novel approach to prevention or treatment of autoimmune diseases.

FOXP3+ regulatory T cells in autoimmune hepatitis are fully functional and not reduced in frequency.

BACKGROUND & AIMS The pathogenesis of autoimmune hepatitis (AIH) is not understood, but it was suggested that AIH may be related to a numerical or functional impairment of CD4+CD25+FOXP3+ regulatory T cells (Treg), which are important mediators of immune tolerance to self-antigens. However, the role of Treg in AIH is not clear, since earlier studies reporting Treg impairment had used only CD25 as marker that cannot unambiguously distinguish Treg from activated effector T cells. METHODS We assessed the frequency and suppressor function of Treg using current staining protocols that can distinguish Treg from activated effector T cells. RESULTS The frequency of CD4+CD25(high)CD127(low)FOXP3+ Treg cells in blood of AIH patients was not reduced compared to healthy subjects, as shown by flow cytometry and confirmed by quantifying Treg-specific demethylation of the FOXP3 gene. Moreover, the suppressor function of Treg isolated from AIH patients was similar to that of Treg isolated from healthy subjects, indicating that Treg function was not impaired in AIH patients. However, we observed that the Treg frequency was significantly higher in those AIH patients with active disease than in those who were in a state of remission, suggesting that the Treg frequency may increase with the degree of inflammation. Indeed, analysis of FOXP3+ Treg in liver histology revealed that the intrahepatic Treg frequency was higher in AIH patients than in NASH patients and correlated with the inflammatory activity of the liver. CONCLUSIONS The frequency and function of circulating Treg cells is not impaired in AIH.

Murine liver antigen presenting cells control suppressor activity of CD4+CD25+ regulatory T cells

CD4+CD25+ regulatory T cells (Treg) are important mediators of peripheral immune tolerance; however, whether Treg participate also in hepatic immune tolerance is not clear. Therefore, we tested the potential of Treg to suppress stimulation of CD4+ T cells by liver sinusoidal endothelial cells (LSEC), Kupffer cells (KC), or hepatocytes. In the absence of Treg, all 3 types of liver cells could stimulate CD4+ T cell proliferation; in the presence of Treg, however, CD4+ T cell proliferation was suppressed. Interaction with KC even stimulated the expansion of the Treg population; LSEC or hepatocytes, in contrast, could not induce proliferation of Treg. Because liver inflammation can be induced by infection, we tested the potential of liver cells to modify Treg suppressor activity in the presence of microbial signals. In the presence of immune‐stimulatory CpG‐oligonucleotides, LSEC, KC, and hepatocytes could indeed overcome Treg‐mediated suppression; in the presence of lipopolysaccharide (LPS), however, only KC and hepatocytes, but not LSEC, could overcome Treg suppressor activity. Hepatocytes from mice with deficient toll‐like receptor‐4 signaling failed to abrogate Treg suppression in response to LPS, indicating that overcoming Treg suppressor activity was indeed a response of the liver cell and not of the Treg. In conclusion, Treg can suppress CD4+ T cell stimulation by liver cells. However, in response to microbial signals, the liver cells can overcome the suppressive activity of Treg. Thus, liver cells may facilitate the transition from hepatic immune tolerance to hepatic inflammation by controlling Treg suppressor activity. (HEPATOLOGY 2005;42:193–199.)

Serologic markers compared with liver biopsy for monitoring disease activity in autoimmune hepatitis.

Goals/Background Disease activity and response to treatment in autoimmune hepatitis is assessed best by liver biopsy, which does not suit for regular disease monitoring. It is frequent clinical practice to follow disease by assessment of serologic markers. Here, we assessed the diagnostic fidelity of this clinical practice. Study One hundred thirty-one biopsies from 82 patients with autoimmune hepatitis were analyzed for histologic activity. Serum samples, taken at the time of biopsy, were analyzed for aminotransferases [alanine aminotransferase (ALT), aspartate aminotransferase], IgG, and γ-globulin levels and compared with histology. Results All serum parameters were significantly associated with histologic activity (P<0.0075); ALT and IgG were most complementary. Presence of both elevated ALT and IgG were associated with high inflammatory activity (histologic activity scores ≥6) with 99% sensitivity. Elevation of either IgG or ALT was associated with residual inflammatory activity in almost all patients. Histologic remission is reliably indicated by normalization of both serum parameters, but about half of the patients with normal serum parameters still showed residual histologic activity of histologic activity index (HAI) 4 or 5. However, our patients with HAI scores 4 or 5 were at significantly lower risk of fibrosis progression than patients with scores ≥6 (P<0.02; odds ratio 14.2). Conclusions Histologic activity seems to be reliably indicated by elevated serum parameters. Normalization of serum parameters is not a reliable marker for complete histologic remission (HAI 1 to 3); however, normalized serum parameters identified patients at low risk of fibrosis progression. Thus, the common clinical practice of disease monitoring by serum markers seems to be suitable for regular follow-up.

Activin A Promotes the TGF-β-Induced Conversion of CD4+CD25-T Cells into Foxp3+ Induced Regulatory T Cells

TGF-β induces the conversion of CD4+CD25− T cells into CD4+CD25+Foxp3+ regulatory T cells (Treg). Activin A is a pleiotropic TGF-β family member and is expressed in response to inflammatory signals. In this study, we report on the effects of activin A on the conversion of CD4+CD25− T cells into Foxp3-expressing induced Treg (iTreg). Activin A was able to promote the conversion of CD4+CD25− T cells into iTreg in a dose-dependent manner in vitro. Activin A together with TGF-β1 had synergistic effects on the rate of iTreg conversion in vitro. Intact TGF-β1 signaling seemed to be essential for the effects of activin A on iTreg generation because cells overexpressing a dominant negative TGF-β type II receptor could not be converted by activin A in vitro. In vivo, the frequency of peripheral, but not central, Treg was increased in transgenic mice with elevated activin A serum levels and the in vivo conversion rate of CD4+CD25− T cells into Foxp3-expressing iTreg was increased as compared with wild type mice. These data suggest a role for activin A as a promoter of the TGF-β dependent conversion of CD4+CD25− T cells into iTreg in vitro and in vivo. Therefore, besides promoting inflammation, activin A may contribute to the regulation of inflammation via the expansion of peripheral Treg.

CXCR3 Deficiency Exacerbates Liver Disease and Abrogates Tolerance in a Mouse Model of Immune-Mediated Hepatitis

The chemokine receptor CXCR3 is preferentially expressed by Th1 cells and critically involved in their recruitment to inflamed tissue. In a mouse model of immune-mediated liver injury inducible by Con A, we investigated the role of CXCR3 in acute IFN-γ–mediated hepatitis as well as in tolerance induction, which has been shown to depend on IL-10–producing CD4+CD25+Foxp3+ regulatory T cells (Tregs). Induction of Con A hepatitis resulted in increased intrahepatic expression of the CXCR3 ligands CXCL9, CXCL10, and CXCL11. CXCR3−/− mice developed a more severe liver injury with higher plasma transaminase activities and a more pronounced Th1/Th17 response compared with wild-type (wt) animals upon Con A injection. Moreover, CXCR3−/− mice did not establish tolerance upon Con A restimulation, although Tregs from CXCR3−/− mice were still suppressive in an in vitro suppression assay. Instead, Tregs failed to accumulate in livers of CXCR3−/− mice upon Con A restimulation in contrast to those from wt animals. Con A-tolerant wt mice harbored significantly increased numbers of intrahepatic CXCR3+T-bet+ Tregs that produced IL-10 compared with nontolerant animals. IFN-γ deficiency or anti–IFN-γ Ab treatment demonstrated that conversion to CXCR3+T-bet+ Tregs depended on a Th1 response. Accordingly, in an immunotherapeutic approach, CD4+CD25+Foxp3+ Tregs from Con A-pretreated CXCR3-deficient mice failed to protect against Con A-induced hepatitis, whereas Tregs from Con A-tolerant wt mice allowed CXCR3-deficient mice to recover from Con A hepatitis. In summary, CXCR3+T-bet+IL-10+ Tregs are generated in the liver in dependence of IFN-γ, then disseminated into the organism and specifically migrate into the liver, where they limit immune-mediated liver damage.

TGF-β-dependent induction of CD4+CD25+Foxp3 + Tregs by liver sinusoidal endothelial cells

BACKGROUND & AIMS CD4(+) CD25(+) Foxp3(+) regulatory T cells (Tregs) have a profound ability to control immune responses. We have previously shown that the liver is a major source of peripherally induced Tregs. Here, we investigate the liver cell types and molecular mechanisms responsible for hepatic Treg induction. METHODS To assess the Treg-inducing potential of liver resident antigen-presenting cell types, we studied the conversion of Foxp3(-) non-Tregs into Foxp3(+) Tregs induced by liver dendritic cells (DCs), liver sinusoidal endothelial cells (LSECs), or Kupffer cells (KCs). The dependency of Treg induction on TGF-β was tested in Treg conversion assays using T cells with reduced TGF-β sensitivity. The suppressive potential of liver cell-induced Tregs was assessed by an in vitro suppression assay and in vivo, in the model of experimental autoimmune encephalomyelitis (EAE). RESULTS All tested liver cell types were capable of inducing Foxp3(+) Tregs; however, LSECs were most efficient in inducing Tregs. Treg-induction was antigen-specific and depended on TGF-β. LSECs featured membrane-bound LAP/TGF-β and the anchor molecule GARP, which is required for tethering LAP/TGF-β to the cell membrane. LSEC-induced Tregs suppressed proliferation and cytokine secretion of effector T cells in vitro. LSEC-induced Tregs were also functional suppressors in vivo, as neuroantigen-specific Tregs induced by LSECs were able to suppress EAE. CONCLUSIONS We demonstrate that LSECs are the major liver cell type responsible for TGF-β dependent hepatic Treg induction. The extraordinary capacity of LSECs to induce Tregs was associated with their unique ability to tether TGF-β to their membrane.

Characteristics and long-term prognosis of the autoimmune hepatitis/primary sclerosing cholangitis overlap syndrome.

Goals/Background Diagnosis, treatment, and prognosis of the overlap syndrome of autoimmune hepatitis (AIH) and primary sclerosing cholangitis (PSC) are controversial. Our aim was to assess the clinical characteristics and long-term prognosis of the AIH/PSC overlap syndrome. Study We reviewed the data of 16 patients seen in our center who fulfilled the diagnostic criteria of both diseases at some stage of their medical history. Results All patients had initially presented with laboratory markers of both, cholestasis and definite AIH. Histologic reexamination of initial biopsies, available from 11 of 16 patients, revealed features of both AIH and PSC in all biopsies. Cholangiography was performed at initial presentation in 9 of 16 patients and appeared normal in 6 of 9 patients. During follow-up cholangiography, an additional 11 patients developed pathologic characteristics of PSC. The age and sex distribution was typical for PSC. Immunosuppressive therapy improved biochemical markers; however, fibrosis was observed to progress in all patients during a median observation period of 12 years. Three patients initially presented with cirrhosis, 12 of 16 patients developed cirrhosis at the end of the observation period, and 3 developed complications of cirrhosis. Conclusions Overlap of AIH and PSC was detected most reliably on grounds of serologic markers and histology; early bile duct changes were often missed by endoscopic retrograde cholangiography. Immunosuppression combined with ursodeoxycholic acid seems to be beneficial, but cannot prevent long-term progression toward cirrhosis in the majority of patients.

Evaluation of F-Actin ELISA for the Diagnosis of Autoimmune Hepatitis

OBJECTIVE:Antibodies to F-actin have been proposed to increase specificity in the diagnosis of autoimmune hepatitis (AIH). We compared the diagnostic value of a new F-actin enzyme-linked immunosorbent assay (ELISA) with the current gold standard of detection of smooth muscle antibodies by indirect immunofluorescence (SMA-IFT).METHODS:Archived sera of 47 patients with SMA positive AIH were tested with the F-actin ELISA and SMA-IFT. Prospectively collected sera of 123 patients with various liver diseases, 35 of whom had AIH, were analyzed by both assays. Different cutoff limits were considered for the F-actin ELISA (increments between 20 and 60 ELISA units) and SMA-IFT (titers of 1:40, 1:80, and 1:160).RESULTS:The F-actin ELISA had a sensitivity of 100% to detect all of 47 SMA positive AIH sera and the value of the ELISA units correlated with that of SMA titers (p < 0.0001). In prospective analysis, F-actin ELISA showed a superior sensitivity (74% vs 34%) and a similar specificity (98% vs 99%) and positive predictive value (88% vs 92%), compared with SMA-IFT. Combining both assays improved neither sensitivity nor specificity.CONCLUSIONS:The new F-actin ELISA seems to be a useful diagnostic tool with similar specificity and superior sensitivity for the diagnosis of AIH, compared with standard SMA-IFT. Due to its simplicity and operator independency, the F-actin ELISA may become a preferred screening technique for detection of autoantibodies in patients with suspected AIH.