This paper has been retracted by its authors and the journal's Editor-in-Chief because irregularities have been identified in some of the figures that render two of its major conclusions unsound: (i) that both human adipose tissue-derived mesenchymal stem cells and bone marrow-derived mesenchymal stem cells express all of the five sphingosine-1-phosphate-receptors; and (ii) that no significant changes were observed in cells grown under the different culture conditions.