Paediatric Autoimmune Liver Disease.

In paediatrics, there are 2 liver disorders in which liver damage most likely stems from an autoimmune attack: 'classical' autoimmune hepatitis (AIH) and the AIH/sclerosing cholangitis overlap syndrome (also known as autoimmune sclerosing cholangitis, ASC). The presentation of childhood autoimmune liver disease (AILD) is non-specific and can mimic most other liver disorders. AIH is exquisitely responsive to immunosuppressive treatment, which should be instituted promptly to prevent rapid deterioration and promote remission and long-term survival. Difficult-to-treat or non-responsive patients should be treated with mycophenolate mofetil; if this fails then calcineurin inhibitors can be tried. Persistent failure to respond or lack of adherence to treatment result in end-stage liver disease. These patients, and those with fulminant liver failure at diagnosis, will require liver transplantation. ASC responds to the same immunosuppressive treatment used for AIH when treatment is initiated early. Abnormal liver function tests often resolve within a few months of treatment, although medium- to long-term prognosis is worse than that of AIH because bile duct disease continues to progress despite treatment in approximately 50% of patients. Ursodeoxycholic acid is usually added to conventional treatment regimen in ASC, but whether this actually helps arrest the progression of bile duct disease remains to be established. The pathogenesis of paediatric-onset AILD is not fully understood, although there is mounting evidence that genetic susceptibility, molecular mimicry and impaired immunoregulatory networks contribute to the initiation and perpetuation of the autoimmune attack. Liver damage is thought to be mediated primarily by CD4pos T-cells. While Th1 effector cells are associated with hepatocyte damage in both AIH and ASC, Th17 immune responses predominate in the latter where they correlate with biochemical indices of cholestasis, indicating that IL-17 is involved in the bile duct damage characteristic of this condition. Since a substantial difference between these 2 pathologies is the frequent association of ASC with inflammatory bowel disease, it can be speculated that lymphocytes of intestinal origin are present in patients with a diagnosis of ASC rather than in those with AIH. Animal models faithfully representing the human conditions are needed to unravel the contribution of innate and adaptive, effector and regulatory immune responses. A deeper understanding of the pathogenesis of AILD is likely to contribute to the development of novel treatments, such as the adoptive transfer of autologous expanded antigen-specific regulatory T-cells, which ultimately aim at restoring tolerance to liver-derived antigens.