Introduction Autoimmune hepatitis (AIH)/sclerosing cholangitis overlap syndrome (autoimmune sclerosing cholangitis, AISC) is a severe hepatopathy that, in addition to the serological and histological features typical of AIH (hyper γ globulinaemia, autoantibody seropositivity and interface hepatitis), presents with bile duct abnormalities. Both conditions are associated with numerical and functional impairment of CD4⁺CD25^high regulatory T cells (Tregs), a lymphocyte subset central to immune-tolerance. It remains unclear whether the two conditions can be distinguished on the basis of specific immune-regulatory T cell defects. To this end, we have explored a subset of Tregs expressing CD39, an ectoenzyme that contributes to Treg suppression by hydrolysing pro-inflammatory nucleotides and whose polymorphisms are associated with autoimmune disease in humans.

Methods We studied 10 patients with AISC (2 females, median age: 14.5 years), 24 with AIH type 1 (12 females, median age: 16 years) and 25 healthy subjects (HS; 15 females, median age 36 years). The frequency and phenotype of circulating CD4⁺CD39⁺CD25^high cells (CD39⁺Tregs) was assessed by flow cytometry using monoclonal antibodies to CD4, CD25, CD39, CD127 and FOXP3. The frequency of IFNγ, IL17 and TGFß-producing CD39⁺Tregs was determined by intracellular cytokine staining.

Results The frequency of CD39⁺Tregs was markedly reduced in AISC (0.31±0.11) compared to AIH (4.30±0.89, p<0.01) and HS (7.02±1.28, p<0.01). AISC patients also had fewer CD39⁺FOXP3⁺Tregs (0.03±0.02) and CD39⁺CD127⁻Tregs (0.05±0.02) than AIH patients (FOXP3⁺: 0.14±0.03, p=0.05; CD127⁻: 0.42±0.10, p<0.01) and HS (FOXP3⁺: 0.20±0.04, p=0.03; CD127⁻: 0.49±0.07, p=0.01). Analysis of cytokine profiles showed that in AISC there was a higher frequency of CD39⁺Tregs producing IFNγ (0.23±0.15) and IL17 (0.22±0.14) and a lower frequency of CD39⁺Tregs producing TGFß (0±0) than in AIH (IFNγ: 0.04±0.02, p=0.05; IL17: 0.03±0.01, p=0.03; TGFß: 0.03±0.01, p=0.09) and HS (IFNγ: 0.07±0.03 p=0.13; IL17: 0.06±0.03, p=0.11; TGFß: 0.02±0.01, p=NS).

Conclusion Compared to AIH and health, CD39⁺Tregs in AISC are reduced in frequency and display a more proinflammatory cytokine profile. These findings suggest that immune-regulation impairment is more severe in AISC than AIH and implicate CD39 as a marker to differentiate immune-regulatory T-cell defects in the two conditions.

Competing interests None declared.