Age-related changes of the function and amount of natural killer cells in the liver: experiment with mice

Abstract

To investigate the age-related changes of the function and amount of natural killer (NK) cells in the liver. C57BL/6 mice aged 2 weeks and 8 weeks were killed and their livers and spleens were taken out. The percentages and absolute values of the NK cells in the livers and spleens were examined by flow cytometry. Using YAG-1 cells as the target cells, the cytotoxicity of the NK cells was detected. Using thymocytes of the homologous mice as the target cells, the cytotoxicity of the NK T cells was detected. The cytotoxicity of the cytotoxic T lymphocytes (CTLs) was detected with the EL-4 cells as the target cells. RT-PCR was used to detect the mRNA expression of perforin. The NK cell percentage in the liver of the 2-week-old mice was 11.9% +/- 1.7%, not significantly different from that of the 8-week-old mice (9.9% +/- 1.6%, P > 0.05). The NK cell amount of per weight liver tissue of the 2-week-old mice was (11.6 +/- 2.5) x 10(5)/g, significantly higher than that of the 8-week-old mice, (3.4 +/- 0.8) x 10(5)/g, (P < 0.05). The cytotoxicity of the liver NK cells of the 2-week-old mice was 71.0% +/- 5.5%, significantly higher than that of 8-week-old mice (23.8% +/- 4.4%, P < 0.05). The cytotoxicity levels of the NK T cells and CTLs were not significantly different between the mice of different age. The cytotoxicity level of the spleen NK cells was not significantly different between the 2-week-old and 8-week-old mice as well. Phenotypic characterization showed that the NK cells in the liver of the 2-week-old mice were CD69(high) MAC-1(low) LY49C/1(low), whereas those in the liver of the 8-week-old mice were inverse, i.e., CD69(low) MAC-1(high) LY49C/1(high). The level of perforin mRNA was remarkably higher in the lever of the 2-week-old mice than in the liver of the 8-week-old mice. The liver NK cells of the young mice have a higher level of cytotoxicity and a unique phenotype. The liver of young mice has its unique microenvironment and their liver NK cells have a special development pathway.