Biologic responses of PCs to mpCCL2. (A) MSC CM leads to CD19⁻CD138⁺ cell proliferation. After treatment of splenocytes with MSC CM, CD138⁺ gating demonstrates that the cells proliferate as of day 1, whereas the addition of CCL2 neutralizing antibody blocks this proliferative activity. The same profile was noticed for days 2 and 3. (B) MSC CM leads to plasmablast proliferation. No apparent CD138/CD19 double-positive cells could be found after a 3-day culture with splenocyte media (control group). However, a high percentage of plasmablast is detectable (17%) when cultured with MSC CM with a decrease to 10% after CCL2 neutralization. (C) CCL2 neutralization leads to IL-10 secretion. From the same experiments performed in panel A, IL-6 and IL-10 ELISAs were performed. IL-6 does not seem to be altered if CCL2 is neutralized, whereas IL-10 is up-regulated (n = 3/group; P < .005).