UC-MSCs prevented tissue damage and inflammatory responses in CIA. (a) Treatment was begun after the onset of disease (arthritis score≥1). PBS and PBS containing 1 × 106 UC-MSCs were injected intraperitoneally each day for five days to mice with CIA. The severity of CIA was progressively attenuated in UC-MSCs treated mice, as compared with PBS treated mice. N = 10, **P < 0.01, vs. the PBS controls. All the data are expressed as the mean ± SD. (b) H & E-stained sagittal sections of joints from CIA mice. PBS treated mice showed a marked mononuclear cell infiltration, severe synovitis, pannus formation and bone erosion. However, the majority of joints from mice injected with UC-MSCs had normal morphology with a smooth articulation cartilage surface, and an absence of inflammatory cell infiltrate and pannus formation. Original magnification × 100. N = 10, **P < 0.01, vs. the PBS controls. All the data are expressed as the mean ± SD. (c) UC-MSCs treatment reduced inflammatory responses in CIA. There were reduced levels of proinflammatory cytokines and chemokines (TNF-α, IL-6 and MCP-1) and increased levels of the anti-inflammatory/regulatory cytokine (IL-10) in sera of UC-MSC-treated mice, in comparison with PBS treated mice. N = 10, ** P < 0.01, * P < 0.05, respectively. All the data are expressed as the mean ± SD. (d) UC-MSCs were detected in the spleen of CIA mice. mAb against human nuclei was used to detect human UC-MSCs in CIA mice, on Day 3 and Day 7, UC-MSCs were detected in the spleen. Arrows indicate human UC-MSCs in the spleen. Original magnification × 200. (e) DTH responses in UC-MSC-treated or untreated CII immunized mice. Values are the mean ± SD. N = 5.