PDGF but not VEGF in the CLL-CM is able to activate MSC PDGFR. (A) Variable levels of PDGF and VEGF were detected in CLL-CM. The line in each dot plot represents the mean level of detected growth factor. (B) RTK array analysis of CLL MSC stimulated by CLL-CM for 30 minutes in the presence or absence of neutralizing antibody to PDGF, VEGF, or both. RTK array analysis of CLL MSC was performed in the presence of either PDGF-AB or VEGF-A ligand. (C) Immunoblot analysis demonstrating the presence of PDGF-AB in CLL B cells. PDGF-AB was up-regulated when CLL B cells were cultured under hypoxic conditions after overnight culture in 3 of 4 patients tested. CLL 1-4, 4 CLL patient lysates used in the immunoblot. Four different CLL samples were run on separate gels and are shown. Each gel is shown in separate rectangle.