Background: Thus far, human hepatic Ito (fat-storing) cell lines have not been established. Therefore, functional characteristics of Ito cells have not been fully investigated.
Experimental design: We established a new cell line, LI90, that exhibited characteristics compatible with those of Ito cells from a human hepatic mesenchymal tumor. LI90 cells were examined with phase-contrast microscopy, immunohistochemistry, and cytogenetics, and their vitamin A-storing activity was analyzed. To obtain a marker specific for Ito cells for immunohistochemical analyses, we raised mAb against LI90 cells and clarified the molecular nature of the Ag recognized with the new Ab using an expression cloning approach.
Results: LI90 cells showed polygonal shape and had well developed alpha-smooth muscle actin filaments in their cytoplasm. In an overconfluent culture condition, LI90 cells aggregated to form a typical hills-and-valleys structure, LI90 cells produced various connective tissue components, such as collagen types I, III, IV, V, and VI, laminin, and fibronectin. In culture media containing vitamin A, LI90 cells formed many fat droplets in their cytoplasm, and fluorescence characteristic of vitamin A was observed in the droplets. By immunizing mice with LI90 cells, three separate mAb specifically reacting with Ito cells in human liver sections were established, and the Ag recognized with all three Ab were identified as extracellular matrix tenascin.
Conclusions: The above-described morphologic and functional characteristics, including vitamin A-storage and biosynthesis of tenascin, are compatible with those of Ito cells. Therefore, LI90 cells will be useful for in vitro studies of functions of human Ito cells.