CD4+CD25+Foxp3+ T-regulatory (Treg) cells control immune responses and maintain immune homeostasis. Recently, it is reported that Treg cells produce pro-inflammatory cytokines under inflammatory conditions. However, the inflammatory cytokine producing Treg cells has not been reported in human viral diseases. We investigated inflammatory cytokine-producing Treg cells, especially TNF-α-producing Treg cells in patients with acute hepatitis A (AHA), which is caused by hepatitis A virus infection.
First, we examined inflammatory cytokine production (IFN-γ, IL-17A, and TNF-α) by Treg cells from AHA patients compared to healthy controls upon TCR stimulation by flow cytometry. We found that compared to Treg cells from healthy controls, AHA patients produced significantly more of all three cytokines. Of the three cytokines, the production of TNF-α was most prominent. To examine epigenetic stability of TNF-a-producing Treg cells, we analyzed the methylation status of highly conserved CpG islands located in the TSDR, as methylation of this region controls Foxp3 expression, and found that TNF-a-producing Treg cells are bona fide Treg cells. Next, we investigated phenotypical and functional characteristics of TNF-α-producing Treg cells. TNF-α-producing Treg cells had features of Th17 cells, including up-regulation of RORγt, which was required for TNF-a-production. And TNF-a-producing Treg cells had reduced suppressive functions compared to TNF-α-non producing Treg cells. Moreover, we found that the frequency of TNF-α-producing Treg cells in AHA patients’ blood correlated with their serum level of alanine aminotransferase.
In conclusion, Treg cells from patients with AHA have altered functions, compared with healthy individuals. Treg cells from patients with AHA produce higher levels of TNF-α, gain features of Th17 cells, and have reduced suppressive activity. TNF-α-producing Treg cells are associated with liver injury in patients with AHA. Taken together, this study provides new insight into the functional change of Treg cells during human acute viral hepatitis by demonstrating the inflammatory conversion of Treg cells.