IL-17 is mainly produced by a distinct subset of CD4+ T helper cells called Th17 cells. IL-17 may be a new marker for the severity of acute hepatic injury since levels increase in patients with severe acute hepatic injury or fulminant hepatic failure . Liver infiltration of IL-17+ T cells has also been found to be positively associated with the grade of liver inflammation in CHB patients . In fact, most experimental evidence to date suggests a role for IL-17 family members in the coordination of local tissue inflammation, mainly via the induced release of pro-inflammatory and neutrophil-mobilizing cytokines . It has been found that the frequency of circulating IL-17+ T cells increases with disease progression from CHB to ACLF .
To understand whether the frequency of intrahepatic IL-17+ T cells increases during the course of HBV-related ACLF just as the frequency of circulating IL-17+ T cells does, we performed immunochemistry staining of IL-17 and CD4 in liver biopsies from 57 patients with HBV related end-stage liver diseases. The frequency of intrahepatic IL-17+ T cells and the IL-17+/CD4+ ratio increased significantly in HBV-related ACLF and CLF patients, and the increase in IL-17+ T cells positively correlated with Tbil, CHOL and MELD score. Therefore, the increase in IL-17+ T cells can reflect the grade of hepatic injury during the progression of liver disease. Inappropriate, excessive, or non-specific IL-17+ T cell effector responses may be involved in the pathogenesis of HBV-related ACLF. However, little is known about the regulatory role of IL-17+ T cells in HBV infection. An in vitro study by Li, J et al. has demonstrated that HBcAg can stimulate the production of IL-10, which negatively regulates HBcAg-specific Th17 cell responses in CHB patients . Similar findings in a study of chronic hepatitis C virus (HCV) has also revealed that HCV-specific Th1 and Th17 cells are suppressed by HCV nonstructural protein 4 (NS4) -induced production of IL-10 and transforming growth factor (TGF)-β .
Th17 and Treg, which are two subsets of CD4+T cells, share reciprocal developmental pathways in immune responses. The generation of Treg cells is dependent on a critical differentiation factor named TGF-β . An experiment in mice demonstrated that the generation of Foxp3+ Treg cells can be completely inhibited by IL-6 induced during inflammation, while the differentiation of pathogenic Th17 cells from naive T cells is induced by IL-6 plus TGF-β. Notably, a more recent study has suggested that Th17 cells play a crucial role in the mediation of airway inflammatory responses and that antigen-specific Treg cells suppress Th17-mediated lung inflammation .
Immunochemistry staining of Foxp3 was used to determine the number of Treg cells infiltrating the liver tissue since Foxp3 is not only a transcription factor but also a specific marker for Treg . Our result showed that the frequency of Foxp3+ T cells increased significantly in HBV-related ACLF and CLF patients compared to NC, but there was no significant difference between the CLF and ACLF patients. Xu et al. have found that the frequency of Foxp3+ Treg cells increased dramatically in the circulation and liver of 9 patients with chronic severe hepatitis B, and that the increase in Treg at the inflammatory site is associated with the chronicity and severity of liver inflammation . Our finding that Foxp3+ T cells in the ACLF and CLF patients were similar is in contrast to that study, probably because the patients enrolled in our study suffered from severe and end-stage liver diseases. As a result, there was a small increase in Foxp3+ T cells but they were unable to suppress the inflammation, leading to massive hepatic necrosis and thereafter, to poor prognosis.
The IL-17+/Foxp3+ ratio in the ACLF patients was higher than that in CLF patients, which suggests that the number of IL-17+ T cells increased and caused immune hepatic injury in the progression of ACLF. However, although the numbers of suppressive Foxp3+ T cells increased a little, they did not reach the same proportion as the IL17+ T cells, leading to a relative shortage of suppressive factors. This suggests that the imbalance of the IL-17+/Foxp3+ ratio in the liver infiltrating lymphocytes may be the key factor for the development of fatal ACLF.
CD8+ T cells participate in the elimination of HBV and may cause sustained liver damage  while Treg cells have a negative regulatory function. Previous studies on chronic hepatitis C have found that human CD4+ CD25+ T cells can cause pronounced and sustained inhibition of CD8+ T cell proliferation [25, 26]. Franzese et al  have found that the frequencies of CD4+CD25+Treg cells showed no significant difference in patients with immunotolerant, chronic active and asymptomatic HBV infections, while the decrease in CD4+ CD25+ T cell frequency was found in patients with a flare-up of chronic hepatitis B. An in vitro study showed that depletion of the CD4+ CD25+ T cell population affected not only the expansion of HBV-specific CD8+ T cells but also their function . This confirms the ability of circulating CD4+ CD25+ T cells to suppress antiviral immune responses mediated by CD8+ T cells [25, 28]. CD4+ CD25+ T cells are activated to suppress the expansion of HBV-specific CD8+ T cells, thus precluding HBV clearance but limiting excessive immune-mediated liver damage. This regulation is clearly non-antigen specific .