The effects of serum PDGF-AA and –BB on MSC proliferation. A) Proliferation indices (PIs), measured by xtt assay, of sera derived from six patients at two time-points; adjacent bars represent Day 0 Baseline and the second time point; C represents negative control FCS, error bars represent technical replicates. PIs were normalised to control NH media (PI =1). B) Platelet levels in PB of the same six patients taken at the same two time-points. C) PDGF-AA and -BB levels in PB of the same six patients taken at the same two time-points. D) White cell levels in PB of the same six patients taken at the same two time-points. Patterns in PI changes are similar to changes in PDGF-AA and -BB levels and platelet counts but not WCC counts. E and F) Positive correlations between changes in sera PIs and changes in the corresponding levels of PDGF-AA, −BB and platelets, in the same patient (<1 decline, >1 increase). MSC, mesenchymal stem cell; NH, non-haematopoietic; PB, peripheral blood; PDGF, platelet-derived growth factor; WCC, white cell count.