Effects of hOCIF and mOPG on cell proliferation of mammary tumor cells in vitro. To examine whether hOCIF is able to directly suppress cell proliferation, we examined the effect of hOCIF on the proliferation of 4T1 (A), CL66 (B), and CL66M2 (C) cells in vitro and the effect of mOPG on the proliferation of 4T1 (D), CL66 (E), and CL66M2 (F) cells in vitro. mOPG, but not hOCIF, suppressed the proliferation of all three cell lines in vitro, suggesting that mOPG but not hOCIF, may have directly suppressed the proliferation of mammary tumor cells in vivo. *, **, *** p < 0.05, p < 0.01, p < 0.001.