MSC injection in vivo decreases IgG titers. (A) MSC injection in OVA-immunized mice can lead to faster clearance of IgG titers. After immunization of B6 mice with rOVA, MSCs were injected intraperitoneally at 4-week intervals and bled weekly for anti-OVA IgG titer by ELISA. MSCs led to a faster decrease in IgG levels as opposed to the control group. (B) ELISPOT assay using CCR2^−/− cells. CCR2^−/− mice are not affected by MSCs. CCR2^−/− mice were immunized with rOVA along with WT B6 mice and injected with MSC as explained in panel A. High IgG titers were developed in CCR2^−/− with no significant decrease after MSC injection. (C) Total IgG titers. In vitro ELISPOT performed with CCR2^−/− and WT B6 splenocytes demonstrates that CCR2^−/− cells are refractory to antagonist CCL2 (n = 3/group). (D) Total IgG titers. Total IgG levels screened by ELISA shown that the overall circulating IgGs were not affected by MSC injection.