Galectin-9 preferentially induces apoptosis of lymphoid T cells but not myeloid cells and MM cell line cells. (A) CD14⁺ monocytes were stimulated with RANKL and M-CSF. Supernatant was collected to measured Galectin-9 by ELISA, (B) serum was obtained from 5 healthy donors, and simultaneous serum and BM plasma were obtained from 10 MM patients. Galectin-9 level was determined by ELISA. (C) PBMCs from healthy donors and 3 MM cells were treated with recombinant Galectin-9 (1 μg/mL) for 12 hours, stained with Annexin V/PI, and analyzed by flow cytometry. Bottom right quadrants represent early apoptotic cells (Annexin V-positive only) and top right quadrant the late apoptotic cells (Annexin V- and PI-positive). *P < .05; **P < .001; by unpaired 2-sided Student t test. PI, propidium iodide.