Background & AimsMucosal-Associated Invariant T (MAIT) cells are innate-like T cells characterised by the invariant TCR-chain, Vα7.2-Jα33, and are restricted by MR1, which presents bacterial vitamin B metabolites. They are important for antibacterial immunity at mucosal sites; however, detailed characteristics of liver-infiltrating MAIT (LI-MAIT) and their role in biliary immune surveillance remain unexplored.MethodsThe phenotype and intrahepatic localisation of human LI-MAIT cells was examined in diseased and normal livers. MAIT cell activation in response to E. coli-exposed macrophages, biliary epithelial cells (BEC) and liver B cells was assessed with/without anti-MR1.ResultsIntrahepatic MAIT cells predominantly localised to bile ducts in the portal tracts. Consistent with this distribution, they expressed biliary tropic chemokine receptors CCR6, CXCR6, and integrin αEβ7. LI-MAIT cells were also present in the hepatic sinusoids and possessed tissue-homing chemokine receptor CXCR3 and integrins LFA-1 and VLA-4, suggesting their recruitment via hepatic sinusoids. LI-MAIT cells were enriched in the parenchyma of acute liver failure livers compared to chronic diseased livers. LI-MAIT cells had an activated, effector memory phenotype, expressed α4β7 and receptors for IL-12, IL-18, and IL-23. Importantly, in response to E. coli-exposed macrophages, liver B cells and BEC, MAIT cells upregulated IFN-γ and CD40 Ligand and degranulated in an MR1-dependent, cytokine-independent manner. In addition, diseased liver MAIT cells expressed T-bet and RORγt and the cytokines IFN-γ, TNF-α, and IL-17.ConclusionsOur findings provide the first evidence of an immune surveillance effector response for MAIT cells towards BEC in human liver; thus they could be manipulated for treatment of biliary disease in the future.

Liver transplantation (LT) in children now has a 20-year survival of >80%, but the longterm outcome of these grafts remains uncertain. Serial protocol liver biopsies after transplantation from several pediatric centres have demonstrated the gradual development of unexplained graft inflammation ("idiopathic" posttransplant hepatitis; IPTH) and graft fibrosis in biopsies obtained >12 months post-LT in children with good graft function and (near) normal liver biochemistry. Although the clinical significance of these findings is uncertain, there is evidence to suggest that IPTH may be a form of rejection or chronic antibody-mediated rejection as it is associated with the presence of auto/alloantibodies; de novo Class II donor-specific HLA antibodies (DSA); previous episodes of rejection, and may improve or be prevented with increased immunosuppression. Currently, the only method of diagnosing either hepatitis or fibrosis has been by serial protocol biopsies as neither serum markers of fibrosis nor noninvasive methods to detect fibrosis such as transient elastography (TE) are sufficiently validated in children. This review will focus on the diagnosis and management of idiopathic posttransplant hepatitis and graft fibrosis, discuss current methods for detecting graft injury, and potential mechanisms for their development. Liver Transplantation 22 1593-1602 2016 AASLD.

To describe etiology, short-term outcomes and prognostic accuracy of serial PELD scores in PALF. Retrospective analysis of children aged ≤16 yr, admitted with PALF under the QLTS, Brisbane, Australia, between 1991 and 2011. PELD-MELD scores were ascertained at three time points (i) admission (ii), meeting PALF criteria, and (iii) peak value. Fifty-four children met criteria for PALF, median age 17 months (1 day-15.6 yr) and median weight 10.2 kg (1.9-57 kg). Etiology was known in 69%: 26% metabolic, 15% infective, 13% drug-induced, 6% autoimmune, and 9% hemophagocytic lymphohistiocytosis. Age <3 months and weight <4.7 kg predicted poor survival in non-transplanted children. Significant independent predictors of poor outcome (death or LT) were peak bilirubin > 220 μm/L and peak INR > 4. Serial PELD-MELD scores were higher in the 17 (32%) transplant recipients (mean: [i] 26.8, [ii] 31.8, [iii] 42.6); highest in the 12 (22%) non-transplanted non-survivors (mean: [i] 31.6, [ii] 37.2, [iii] 45.7) compared with the 25 (46%) transplant-free survivors (mean: [i] 25.3, [ii] 26.0, [iii] 30.3). PELD-MELD thresholds of ≥27 and ≥42 at (ii) meeting PALF criteria and (iii) peak predicted poor outcome (p < 0.001). High peak bilirubin and peak INR predict poor outcome and serial PELD-MELD is superior to single admission PELD-MELD score for predicting poor outcome.