Immune dysregulation in Alagille syndrome: A new feature of the evolving phenotype.

Alagille syndrome (ALGS) is a rare autosomal dominant, multi-system disease caused by mutations in one of two NOTCH signaling pathway genes. Mutations in JAG1 are found in more than 94% of patients, with associated Jagged1 defects. We previously showed that CD46, which is a complement and immune regulator, regulates NOTCH expression during T cell activation after binding to C3b/C4b. We have identified 25% of our ALGS cohort with frequent infections and studied a subgroup of 4 in detail who were not showing current features of infections in order to show if Jagged1 abnormalities could affect immune function. We used cytometric bead arrays and FACS to measure cytokines and cell membrane expression. Resting and activated T cells were studied in both low and high IL-2 concentration to assess the TH1 ability to shift from INFγ to IL-10 production. In vitro initial PBMC cell population and subpopulation assessment were normal but further assessment of the lymphocytes revealed that while NOTCH1 expression and regulation was normal on resting TH1, Jagged1 expression was exaggerated. Resting TH1 cells from some patients exhibited high CD132 levels. Upon activating T cells, TH1 cells managed to produce TNF but failed to produce sufficient IFNγ levels (in two patients TH1 produced no IFNγ). TH2 exhibited exaggerated response with high IL-4 and IL-5 levels. TH1 were unable to down-regulate CD127, resulting in prolonged immune activation, and failed to shift from IFNγ to IL-10 production maintaining high IL-2 levels suggesting an impaired T cell response. Disturbed CD46-Jagged1 interaction may explain recurrent infections among ALGS patients, and could predispose to Th2-driven conditions such as asthma, eczema, food allergies and airway atopy and otitis media. The ALGS description could now be extended to include immune dysregulation.

The CD46-Jagged1 interaction is critical for human TH1 immunity.

CD46 is a complement regulator with important roles related to the immune response. CD46 functions as a pathogen receptor and is a potent costimulator for the induction of interferon-γ (IFN-γ)-secreting effector T helper type 1 (T(H)1) cells and their subsequent switch into interleukin 10 (IL-10)-producing regulatory T cells. Here we identified the Notch family member Jagged1 as a physiological ligand for CD46. Furthermore, we found that CD46 regulated the expression of Notch receptors and ligands during T cell activation and that disturbance of the CD46-Notch crosstalk impeded induction of IFN-γ and switching to IL-10. Notably, CD4(+) T cells from CD46-deficient patients and patients with hypomorphic mutations in the gene encoding Jagged1 (Alagille syndrome) failed to mount appropriate T(H)1 responses in vitro and in vivo, which suggested that CD46-Jagged1 crosstalk is responsible for the recurrent infections in subpopulations of these patients.

The significance of human jagged 1 mutations detected in severe cases of extrahepatic biliary atresia.

Mutations of human jagged 1 (JAG1) gene are responsible for Alagille Syndrome (AGS), whose 2 main symptoms are intrahepatic bile duct hypoplasia and pulmonary stenosis. We examined the JAG1 mutation in extrahepatic biliary atresia (EHBA), which is similar in phenotype to AGS, although a different pathogenesis is suggested. In 102 cases of EHBA, 9 missense mutations were detected, including 2 intrafamilial expressions in the propositus and an aunt of one family. These mutations were all missense and sporadic except for those of this particular family. The JAG1 gene mutations were generally found in severely ill patients subjected to liver transplantation at less than 5 years of age. None of the 9 cases of EHBA revealed any of the 5 major symptoms of AGS nor any identical pathological findings after 3 years of follow-up. Our cases were clearly separated from AGS by pathological findings and clinical features, and could be diagnosed as EHBA and not as atypical AGS. The increase of interleukin 8 (IL-8) production induced by tumor necrosis factor alpha (TNF-alpha) in Huh 7 cells was suppressed by the coexistence of JAG1 protein. We examined the different influences between wild-type cells and the 3 kinds of mutants detected in EHBA on Huh 7 cells and found that 2 of 3 mutants showed about half of the repressed activity compared with that of wild type. In conclusion, these results suggest that the JAG1 gene abnormality may be an aggravating factor in EHBA.