The impact of interferon gamma receptor expression on the mechanism of escape from host immune surveillance in hepatocellular carcinoma

Interferon gamma (IFN-gamma) plays an important role in host defense mechan ism and participates in the progression of chronic liver disease. IFN-gamma exerts its pleiotrophic effects by transcriptional regulation of expressio n of numerous genes, such as major histocompatibility complex (MHC) class I and Fas, through interaction with IFN-gamma receptor (IFN-gamma-R). Althou gh hepatocytes in normal liver express weak or no IFN-gamma-R, those in acu te and chronic liver disease up-regulate its expression. A study using IFN- gamma-R alpha-chain knock-out mice revealed the actions of IFN-gamma on tum or cells as an extrinsic tumor-suppressor mechanism. However, it is unclear whether or how hepatocellular carcinoma (HCC) blocks the signal transducti on of IFN-gamma to evade host immune surveillance. We examined the expressi on of IFN-gamma-R and IFN-gamma-inducible genes in 44 cases with HCC using real-time reverse-transcriptase polymerase chain reaction (RT-PCR) and immu nohistochemistry. In noncancerous liver tissues (n = 38), IFN-gamma-R expre ssion on the cell surface was upregulated in 27 cases. In IFN-gamma-R-negat ive cases (n = 15), tumor size was larger (P = .032), serum alpha-fetoprote in (AFP) level was higher (P = .001), intrahepatic and extrahepatic metasta sis was more common (P = .044 and .013, respectively), and Ki-67 labeling i ndex (LI) was higher (P = .041), compared with IFN-gamma-R-positive cases. Accordingly, the evasion mechanism may play an important role in progressio n, especially metastasis, in HCC. The significant correlation between the s tatus of IFN-gamma-R and the expression of Fas and MHC implies that the los s of IFN-gamma-R might contribute to the mechanism of escape from host immu ne rejection in HCC.