hMSCs inhibit immunoglobulin production. Purified B cells were incubated for 7 days without or with hMSC at a 1:1 ratio in the presence of CpG, rCD40L, anti-immunoglobulin antibodies, IL-2, IL-4, and IL-10. B-cell differentiation was evaluated using 2 assays, namely, quantitation of IgM, IgG, and IgA in culture supernatants by ELISA and enumeration of immunoglobulin-secreting cells by ELISPOT. (A) Median immunoglobulin concentrations (ng/mL), maximum and minimum values from 9 experiments performed by ELISA are shown. ^**P = .003 for IgM and .001 for IgG; *P = .018 for IgA. (B) One representative experiment of the 3 carried out by ELISPOT is shown. Spots indicate immunoglobulin production by individual cells.