To investigate the effects of soluble FGL2 (sFGL2) secreted by hepatic stellate cells (HSCs) on immune suppression in cirrhotic patients with hepatocellular carcinoma (HCC).

Serum sFGL2 levels were examined by ELISA in 40 patients with HCC, liver cirrhosis (LC) or chronic HBV (CHB) infection. A double staining of the immunofluorescence analysis of α-SMA and FGL2 was performed in two cirrhotic liver specimens. The expression of FGL2 in the LX2 cell line was analyzed by immunofluorescence, Western blot and flow cytometry. T-cells purified from HCC patients using magnetic beads were cultured with LX2 cells at different ratios with anti-CD3-stimulating or FGL2-blocking antibodies. The proliferation index (PI) of CD8 + T cells was assessed by flow cytometry, and the secretion of IFN-γ was measured by ELISA.

sFGL2 levels are significantly higher in patients with HCC or LC compared with those with CHB (p = 0.0039/p = 0.0020). Among HCC patients, those with cirrhosis exhibited significantly higher levels of sFGL2 compared with non-cirrhotic individuals (p = 0.0108). The expressions of FGL2 and α-SMA overlapped in HSCs in liver specimens. FGL2 protein secreted by LX2 cells inhibited T-cell proliferation of HCC patients in a dose-dependent manner in vitro. The PI of CD8 + T cells was significantly enhanced following addition of FGL2 antibody to the culture system (LX2/T-cell ratio of 1:10, p = 0.002). The level of IFN-γ in mixed cultures was inversely correlated with the number of HSCs and was reversed by incubation with FGL2 blocking antibody.

sFGL2 protein is a novel effector molecule of activated HSCs, which suppresses CD8 + T cell proliferation and interferon-γ production, and it subsequently might contribute to immune suppression during fibrosis and tumorigenesis in the liver.