STO Feeder Cells Are Useful for Propagation of Primarily Cultured Human Deciduous Dental Pulp Cells by Eliminating Contaminating Bacteria and Promoting Cellular Outgrowth.

STO feeder cells, a line established from mouse SIM embryonic fibroblasts, have been frequently used for establishing embryonic stem cells and maintaining them in an undifferentiated state. There are some reports demonstrating that fibroblastic cells have the ability to phagocytose Gram-positive bacterium (e.g., streptococci and staphylococci). In this study, we examined the possibility that STO cells could phagocytose Streptococcus mutans (a bacteria causing tooth decay), which always contaminates cultures of primarily isolated human deciduous dental pulp cells (HDDPCs). Simple cultivation of the primary HDDPCs in the absence of STO cells allowed S. mutans to massively propagate in the medium, thus leading to an opaque medium. In contrast, there was no bacterial contamination in the cultures containing mitomycin C (MMC)-inactivated STO cells. Furthermore, STO cells indicated bacterial phagocytic activity under fluorescent microscopy with the dye pHrodo. Besides removal of contaminating bacteria, STO feeder cells allowed the HDDPCs to spread out. These data suggest that MMC-treated STO cells can be useful for propagation of HDDPCs by eliminating contaminating bacteria and by promoting cellular outgrowth.