Objectives: To investigate the role of liver natural killer cells (NK cells) in murine hepatitis virus strain 3 (MHV-3) induced murine fulminant hepatitis.
Method: Balb/cJ mice (6-8 weeks, female) were intraperitoneally injected with 100 PFU MHV-3. The numbers of NK cells in their livers, spleens, blood and bone marrow and the expression of CD69 on liver NK cells at 0, 24, 48 and 70 h after MHV-3 infection were analyzed by flow cytometry. The cytotoxic activity of liver NK cells was detected by a non-radioactive cytotoxicity assay. The levels of IFN gamma produced by hepatic NK cells were detected by intracellular cytokine staining.
Result: Following MHV-3 infection, the proportion of liver NK cells in the mice increased remarkably and reached the peak (43.9%+/-2.3%) at 48 h, then kept a high proportion until the mice were sacrificed. The proportion of NK cells in the peripheral blood also significantly increased and reached the peak (18.0%+/-5.4%) at 48 h. However, there were few NK cells in the peripheral blood at 70 h after infection; the ratio was only 1.3%+/-0.6%. In the spleens and bone marrow, the proportions of NK cells were both significantly decreased from 0 h to 48 h and then slightly increased. The expression of CD69 on liver NK cells was highly up-regulated after the infection and the cytotoxic activity of hepatic NK cells at 48 h was also significantly enhanced. In addition, an increase in IFN gamma production by hepatic NK cells was observed at 48 h.
Conclusion: After MHV-3 infection, NK cells were recruited to the liver quickly, probably from the spleen and bone marrow. Recruited NK cells remarkably express CD69, enhance cytotoxic activity and IFN gamma production, which correlate with the disease severity of fulminant viral hepatitis. Our results suggest that liver NK cells may play a pivotal role in the pathogenesis of fulminant viral hepatitis.