Immunophenotype of bone marrow-derived (left) and synovium-derived adherent cells (right). (a) Fluorescence-activated cell sorting of CD marker expression. Results are expressed as the mean fluorescence intensity ± standard error of the mean. One representative experiment out of six different samples of bone marrow mesenchymal stem cells (three normal, two osteoarthritis and one rheumatoid arthritis) and synovium mesenchymal stem cells (two rheumatoid arthritis, two osteoarthritis and two healthy) is shown. Control corresponds to the fluorescence due to the isotypic control. (b) Immunofluorescence staining on cells in a monolayer using the monoclonal antibody specific for human prolyl-4-hydroxylase.