Reply:

We read with interest the letter by Sebode et al., who report in patients with autoimmune hepatitis (AIH) that the frequency of CD4⁺CD25⁺CD39⁺ cells is lower in treated patients when compared to untreated cases. They further note no differences between untreated AIH patients and healthy individuals. The authors propose that regulatory T cell (Treg) impairment results from immunosuppressive treatment rather than being a disease-related defect, as we had previously suggested.¹ Immunosuppressive treatment may indeed impact lymphocyte numbers, including those of CD39⁺ Tregs: for example, in our report,¹ patients treated with prednisolone and mycophenolate mofetil (MMF) had lower proportions of CD39 Treg compared with those who were treated with prednisolone alone or with prednisolone and azathioprine. although such direct effects of the immunosuppressive drugs— MMF in our case—on Treg phenotype are indeed possible, we had posited that the lower frequencies of CD39⁺ Treg observed in the MMF-treated group may reflect more severe disease, characterized by a more substantial regulatory cell impairment.¹ The differences in our results may be due to the fact that, at variance with Sebode et al., we investigated prototypic Tregs that were CD4⁺CD39⁺ and CD25^high. Although we had studied only three patients prior to starting immunosuppressive treatment, interestingly these individuals did not have higher numbers of CD4⁺CD39⁺CD25^high Treg when contrasted with patients on immunosuppressive drugs.

We should add that the involvement of CD39 in the development of autoimmune conditions is suggested by prior observations that genetic polymorphisms associated with low levels of CD39 expression are enriched in patients with Crohn’s disease.² This prior finding infers that lower levels of expression of CD39 by Treg might be linked to an autoimmune diathesis operative through impairment of adenosine generation and perturbation, at least in part, of Treg function.

As suggested by Sebode et al., and agreed to by us, the functional relevance of CD4⁺CD39⁺CD25^high Treg in AIH merits further investigation in larger prospective studies that include both untreated and treated patients.