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Although natural killer (NK) cells are recognized for their modulation of immune responses, the mechanisms by which human NK cells mediate immune regulation are unclear. Here, we report that expression of human leukocyte antigen (HLA)-DP, a ligand for the activating NK cell receptor NKp44, is significantly upregulated on CD8 + effector T cells, in particular in human cytomegalovirus (HCMV) + individuals. HLA-DP + CD8 + T cells expressing NKp44-binding HLA-DP antigens activate NKp44 + NK cells, while HLA-DP + CD8 + T cells not expressing NKp44-binding HLA-DP antigens do not. In line with this, frequencies of HLA-DP + CD8 + T cells are increased in individuals not encoding for NKp44-binding HLA-DP haplotypes, and contain hyper-expanded CD8 + T cell clones, compared to individuals expressing NKp44-binding HLA-DP molecules. These findings identify a molecular interaction facilitating the HLA-DP haplotype-specific editing of HLA-DP + CD8 + T cell effector populations by NKp44 + NK cells and preventing the generation of hyper-expanded T cell clones, which have been suggested to have increased potential for autoimmunity., Competing Interests: Declaration of interests The authors declare no competing interests., (Copyright © 2024 The Authors. Published by Elsevier Inc. All rights reserved.)

Objective: Primary sclerosing cholangitis (PSC) is characterised by bile duct strictures and progressive liver disease, eventually requiring liver transplantation. Although the pathogenesis of PSC remains incompletely understood, strong associations with HLA-class II haplotypes have been described. As specific HLA-DP molecules can bind the activating NK-cell receptor NKp44, we investigated the role of HLA-DP/NKp44-interactions in PSC., Design: Liver tissue, intrahepatic and peripheral blood lymphocytes of individuals with PSC and control individuals were characterised using flow cytometry, immunohistochemical and immunofluorescence analyses. HLA-DPA1 and HLA-DPB1 imputation and association analyses were performed in 3408 individuals with PSC and 34 213 controls. NK cell activation on NKp44/HLA-DP interactions was assessed in vitro using plate-bound HLA-DP molecules and HLA-DPB wildtype versus knock-out human cholangiocyte organoids., Results: NKp44+NK cells were enriched in livers, and intrahepatic bile ducts of individuals with PSC showed higher expression of HLA-DP. HLA-DP haplotype analysis revealed a highly elevated PSC risk for HLA-DPA1*02:01~B1*01:01 (OR 1.99, p=6.7×10 -50 ). Primary NKp44+NK cells exhibited significantly higher degranulation in response to plate-bound HLA-DPA1*02:01-DPB1*01:01 compared with control HLA-DP molecules, which were inhibited by anti-NKp44-blocking. Human cholangiocyte organoids expressing HLA-DPA1*02:01-DPB1*01:01 after IFN-γ-exposure demonstrated significantly increased binding to NKp44-Fc constructs compared with unstimulated controls. Importantly, HLA-DPA1*02:01-DPB1*01:01-expressing organoids increased degranulation of NKp44+NK cells compared with HLA-DPB1-KO organoids., Conclusion: Our studies identify a novel PSC risk haplotype HLA-DP A1*02:01~DPB1*01:01 and provide clinical and functional data implicating NKp44+NK cells that recognise HLA-DPA1*02:01-DPB1*01:01 expressed on cholangiocytes in PSC pathogenesis., Competing Interests: Competing interests: None declared., (© Author(s) (or their employer(s)) 2024. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ.)

Background & Aims: Ulcerative colitis (UC) is characterized by severe inflammation and destruction of the intestinal epithelium, and is associated with specific risk single nucleotide polymorphisms in HLA class II. Given the recently discovered interactions between subsets of HLA-DP molecules and the activating natural killer (NK) cell receptor NKp44, genetic associations of UC and HLA-DP haplotypes and their functional implications were investigated., Methods: HLA-DP haplotype and UC risk association analyses were performed (UC: n = 13,927; control: n = 26,764). Expression levels of HLA-DP on intestinal epithelial cells (IECs) in individuals with and without UC were quantified. Human intestinal 3-dimensional (3D) organoid cocultures with human NK cells were used to determine functional consequences of interactions between HLA-DP and NKp44., Results: These studies identified HLA-DPA1∗01:03-DPB1∗04:01 (HLA-DP401) as a risk haplotype and HLA-DPA1∗01:03-DPB1∗03:01 (HLA-DP301) as a protective haplotype for UC in European populations. HLA-DP expression was significantly higher on IECs of individuals with UC compared with controls. IECs in human intestinal 3D organoids derived from HLA-DP401 pos individuals showed significantly stronger binding of NKp44 compared with HLA-DP301 pos IECs. HLA-DP401 pos IECs in organoids triggered increased degranulation and tumor necrosis factor production by NKp44 + NK cells in cocultures, resulting in enhanced epithelial cell death compared with HLA-DP301 pos organoids. Blocking of HLA-DP401-NKp44 interactions (anti-NKp44) abrogated NK cell activity in cocultures., Conclusions: We identified an UC risk HLA-DP haplotype that engages NKp44 and activates NKp44 + NK cells, mediating damage to intestinal epithelial cells in an HLA-DP haplotype-dependent manner. The molecular interaction between NKp44 and HLA-DP401 in UC can be targeted by therapeutic interventions to reduce NKp44 + NK cell-mediated destruction of the intestinal epithelium in UC., (Copyright © 2023 The Authors. Published by Elsevier Inc. All rights reserved.)

Acute liver failure (ALF) is rare but life-threatening. Common causes include intoxications, infections, and metabolic disorders. Indeterminate etiology is still frequent. No systematic data on incidence, causes, and outcome of ALF across Europe are available. Via an online survey we reached out to European Reference Network Centers on rare liver diseases. Numbers and etiology of ALF cases during 2020 were retrieved and diagnostic and treatment availabilities assessed. In total, 455 cases (306 adult, 149 pediatric) were reported from 36 centers from 20 countries. Intoxication was the most common cause in adult and pediatric care. The number of cases with indeterminate etiology is low. Diagnostic tools and specific treatment options are broadly available within this network. This is the first approach to report on etiology and outcome of ALF in the pediatric and adult population in Europe. High diagnostic yield and standard of care reflects the expert status of involved centers., Competing Interests: The authors report no conflicts of interest., (Copyright © 2023 by European Society for European Society for Pediatric Gastroenterology, Hepatology, and Nutrition and North American Society for Pediatric Gastroenterology, Hepatology, and Nutrition.)

Background & Aims: Primary sclerosing cholangitis (PSC) is characterized by chronic inflammation of the biliary mucosa. Bile ducts in PSC are often colonized with bacteria. Although accumulating evidence demonstrates the importance of microbiota for mucosal immunity, little is known about the impact of bile duct colonization with bacteria on the clinical course of PSC., Methods: Bile samples were sent to culture during endoscopic retrograde cholangio-pancreatography before the administration of peri-interventional antibiotics. Procedures during overt bacterial cholangitis or with prior antibiotic treatment were excluded. The primary endpoint was defined as a composite clinical endpoint of decompensated cirrhosis and/or liver transplantation or death., Results: A cohort of 189 patients with 591 bile fluid cultures was included. In multivariable Cox regression analysis, the presence of Enterococci (present in 28% of the patients), but not of other bacterial species, conferred risk of disease progression with a hazard ratio of 3.61 (95% confidence interval, 1.6-8.11; P = .002) to reach the composite clinical endpoint. Fungobilia, present in 19.6% of patients, was confirmed to associate with disease progression with a hazard ratio of 3.25 (95% confidence interval, 1.87-5.66; P < .001) to reach the composite clinical endpoint., Conclusions: The novel association of biliary colonization by Enterococci with disease progression underlines the importance of microbiota-mucosal interplay for the pathogenesis of PSC. These results should stimulate further mechanistic studies on the role of microbiota in PSC and highlight potential new therapeutic targets for a disease without effective treatment options., (Copyright © 2023 The Author(s). Published by Elsevier Inc. All rights reserved.)

Langerhans cell histiocytosis (LCH) is a very rare cause of secondary sclerosing cholangitis. We report the case of a 42-year-old male patient with sclerosing cholangitis and histological evidence of LCH from a bile duct biopsy. Due to rapid disease progression and exhaustion of conservative therapeutic approaches the patient received a liver transplantation. Nearly 2 years after transplantation the patient has a good graft function and no signs of recurrence of the underlying LCH., (© 2021. Springer Medizin Verlag GmbH, ein Teil von Springer Nature.)

Background: During the current SARS-CoV-2 pandemic it is important to identify risk factors for COVID-19. Registry studies are providing growing evidence on the elevated risk of mortality from COVID-19 in patients with chronic liver disease, especially in advanced stages. Results may, however, have a selection bias towards severe cases. Limited data is available on COVID-19 in patients with autoimmune liver disease (AILD)., Aim: To perform an online survey to capture the prevalence of COVID-19 and the state of medical care of patients with AILD in Europe during the pandemic., Methods: Data was collected via an anonymous patient-oriented, online survey, which was available on the EUSurvey platform in nine European languages between 24 th June 2020 and 14 th October 2020. Of 1834 contributions, 51 were excluded because participants did not name an underlying AILD, and four were excluded because of duplicate data entry., Results: Of 1,779 participants, 1,752 resided in 20 different countries of the European Union and the United Kingdom (UK). The five countries with the highest numbers of contributions were France (n = 450), Germany (n = 318), the Netherlands (n = 267), Spain (n = 225), and the UK (n = 183). 2.2% of participants (39/1779) had been diagnosed with COVID-19. There were no differences regarding age, sex, AILD, the status of liver cirrhosis, or status post liver transplantation between COVID-19 and non-COVID-19 cases. Of the 39 COVID-19 cases, five patients were admitted to a regular ward, one patient was admitted to ICU and required ventilation., Conclusion: In our Europe-wide, patient-oriented survey on COVID-19 in patients with AILD, we detected a low rate of COVID-19, comparable to the period prevalence of the general population. These results suggest that patients with AILD are not at elevated risk of COVID-19., (© 2021 The Authors. United European Gastroenterology Journal published by Wiley Periodicals LLC. on behalf of United European Gastroenterology.)

Hepatocellular carcinoma (HCC) is a global health burden with increasing incidence, poor prognosis and limited therapeutic options. Natural killer (NK) cells exhibit potent anti-tumoral activity and therefore represent potential targets for immunotherapeutic approaches in HCC treatment. However, the anti-tumoral activity of NK cells in HCC associated with different etiologies, and the impact of the heterogeneous NK cell subset, e.g., adaptive and conventional subsets, are not understood in detail. By comparatively analyzing the NK-cell repertoire in 60 HCC patients, 33 liver cirrhosis patients and 36 healthy donors (HD), we show in this study that the NK-cell repertoire is linked to HCC etiology, with increased frequencies of adaptive NK cells in Hepatitis B virus (HBV)-associated HCC. Adaptive NK cells exhibited limited anti-tumoral activity toward liver cancer cells; however, this was not a result of a specific NK-cell impairment in HCC but rather represented an intrinsic feature, since the characteristics of circulating and intra-tumoral adaptive NK cells were conserved between HD, HCC and liver cirrhosis patients. Hence, the expansion of adaptive NK cells with reduced anti-tumoral activity, detectable in HBV-associated HCC, may have implications for tumor surveillance and therapy.

Background & Aims: Phenotypic and functional natural killer (NK)-cell alterations are well described in chronic hepatitis B virus (cHBV) infection. However, it is largely unknown whether these alterations result from general effects on the overall NK-cell population or the emergence of distinct NK-cell subsets. Human cytomegalovirus (HCMV) is common in cHBV and is associated with the emergence of memory-like NK cells. We aimed to assess the impact of these cells on cHBV infection., Methods: To assess the impact of memory-like NK cells on phenotypic and functional alterations in cHBV infection, we performed in-depth analyses of circulating NK cells in 52 patients with cHBV, 45 with chronic hepatitis C virus infection and 50 healthy donors, with respect to their HCMV serostatus., Results: In patients with cHBV/HCMV+, FcεRIγ- memory-like NK cells were present in higher frequencies and with higher prevalence than in healthy donors with HCMV+. This pronounced HCMV-associated memory-like NK-cell expansion could be identified as key determinant of the NK-cell response in cHBV infection. Furthermore, we observed that memory-like NK cells consist of epigenetically distinct subsets and exhibit key metabolic characteristics of long-living cells. Despite ongoing chronic infection, the phenotype of memory-like NK cells was conserved in patients with cHBV/HCMV+. Functional characteristics of memory-like NK cells also remained largely unaffected by cHBV infection with the exception of an increased degranulation capacity in response to CD16 stimulation that was, however, detectable in both memory-like and conventional NK cells., Conclusions: The emergence of HCMV-associated memory-like NK cells shapes the overall NK-cell response in cHBV infection and contributes to a general shift towards CD16-mediated effector functions. Therefore, HCMV coinfection needs to be considered in the design of immunotherapeutic approaches that target NK cells in cHBV., Lay Summary: In chronic hepatitis B virus infection, natural killer (NK)-cell phenotype and function is altered. In this study, we demonstrate that these changes are linked to the emergence of a distinct NK-cell subset, namely memory-like NK cells. The emergence of these memory-like NK cells is associated with coinfection of human cytomegalovirus that affects the majority of patients with chronic hepatitis B., (Copyright © 2018 European Association for the Study of the Liver. Published by Elsevier B.V. All rights reserved.)