Phagocytic and APC functions of MSCs. Macrophages and MSCs were treated with fluorescence microspheres for 2 hours and then examined by confocal microscopy. Three planes are shown in representative microscopic studies from 4 experiments, each performed with cells from different donors: (A) macrophages; (B) MSCs. Activated CD4⁺ cells were immunoselected from PBMCs that were challenged for 5 days with 10 μg/mL C albicans (C) or T toxoid, at 1:100 final dilution (D). Control studies were done in parallel in media alone (Unactivated CD4⁺). Activated CD4⁺ cells were added to autologous MSCs or macrophages, and exposed overnight to C albicans or T toxoid (Pulsed), or to media alone (Unpulsed). Cell proliferation was determined by [methyl-3H]-TdR incorporation, and the results were expressed as stimulation indices (SIs); mean ± SD (n = 6). Background disintegrations per minute (unactivated CD4⁺ and activated CD4⁺) were 308 ± 8 and 140 ± 4, respectively. *P < .05 versus unactivated CD4⁺ cells/pulsed and activated/unpulsed cultures. **P < .05 versus pulsed MSCs + activated CD4⁺ cells.