Cell cycle state of CB-MSC upon HF and control serum treatment. A: Cell cycle status of individual cells was determined after 5 days of HF serum treatment by flow cytometric analysis of DNA content of cells stained with PI. The graphs depict the percentage of cells present in each cell cycle phase. Compared to the human control serum and the FCS group, the number of actively cycling cells in the HF group was significantly lower. B: After 5 days of treatment with either human control, HF serum or FCS, protein expression levels of cyclin dependent kinases (CDK), their positive (cyclins) and negative regulators (CDK inhibitors/CDKI of the INK4A and CIP/KIP family) involved in G1 progression (column 1), G1-S transition (column 2) and M phase entry (column 3) were determined by Western blot. Boxplots display adjusted band densities normalized to FCS for both human treatment groups. HF serum treatment blocks cell cycle progression of CB-MSC through upregulation of p21 and p27. The boxplots indicate interquartile range (box), median (line), range (whiskers) and outliers (+/−).