Background: Although the immunomodulatory effects of mesenchymal stromal cells (MSC) on T cells have been elucidated, little is known about their effects on B cells. Recently, we have established a novel culture method for adipose-derived MSC (ASC) using low (2%) serum medium containing fibroblast growth factor-2. We showed that low serum-cultured ASC (LASC) was superior to high (20%) serum-cultured ASC (HASC) when used in regenerative therapy. The aim of this study was to compare the action of LASC, HASC, and bone marrow-derived MSC (BM-MSC), on xenoantibody production by B cells. Methods: Adipose-derived mesenchymal stromal cells and BM-MSC were obtained from humans or F344 rats and expanded in a low-serum or a high-serum culture medium. Proliferation of human peripheral mononuclear cells (PBMC) or rat splenocytes was induced by phytohemagglutinin (PHA) or anti-IgM-antibody. These cells were then co-cultured with LASC, HASC, or BM-MSC, and cell proliferation was studied. Porcine red blood cells (pRBC) were intraperitoneally injected into Lewis rats, and LASC, HASC, or BM-MSC obtained from F344 rats were injected intravenously or intraperitoneally. The levels of antibodies (IgM and IgG) against pRBC were examined using flow cytometry. Results: Human LASC suppressed PBMC proliferation more effectively than human HASC. Human LASC suppressed both T-cell and B-cell proliferation when incubated with PHA (a T-cell stimulus). However, human LASC did not suppress B-cell proliferation after incubation with anti-IgM-antibody (a T-cell-independent stimulus). Rat LASC suppressed PHA-stimulated splenocyte proliferation more effectively than rat HASC or rat BM-MSC. In vivo studies showed that intravenous injection of rat LASC significantly reduced the levels of IgG antibodies against pRBC, while intravenous administration of the other two types of MSC (rat HASC or rat BM-MSC) or intraperitoneal administration of rat LASC did not impede IgG production. A significant number of LASC were observed in the spleen when injected intravenously while only a few LASC were observed when given intraperitoneally. Conclusions: Administration of LASC effectively impeded xenoantibody production by B cells through the inhibition of T-cell function, while HASC or BM-MSC showed less promising effects. These results suggest that intravenous injection of LASC may be useful in attenuating antibody-mediated rejection.
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