MSC-derived galectin-1 inhibits T-cell proliferation directly. (A) Purified CD4⁺ T cells were stimulated with PHA and cocultured with MSC^wt, MSC^contr, or MSC^G1▾ as indicated. Proliferation of purified CD4⁺ T cells was inhibited by MSC^wt or MSC^contr in the absence of any other cell type. Proliferation of purified CD4⁺ T cells was less affected by the presence of MSC^G1▾ compared with MSC^wt or MSC^contr. These experiments show that MSC-derived galectin-1 suppresses T cells directly in the absence of other cell types. (B) IL-12 secretion of monocyte-derived DC after coculture with MSCs. Monocytes were incubated with IL-4 and granulocyte-macrophage colony-stimulating factor alone and in the presence of MSC^wt, MSC^contr, or MSC^G1▾ (ratio 1:10 MSC/monocytes) for 5 days. The proinflammatory cytokine IL-12 was measured after maturation with LPS for 20 hours in the supernatant. IL-12 secretion of DC was suppressed to the same extent by MSC^wt, MSC^contr, and MSC^G1▾. All data are shown as means (± SE) of 6 independent experiments.