Fig. 5. Effects of PDGF-BB on cartilage particle development. The sorted flk-1^–PDGFR⁺ cells (A) and flk-1⁺PDGFR^– (B) were subjected to the pellet culture in the presence of TGFß3 (a-c,g-i), or TGFß3 and 50 ng/ml PDGF-BB (d-f,j-l). Particles formed after 17 days of culture were fixed with Gendre's fluid, paraffin-embedded, sectioned and stained with Toluidine blue (a,d,g,j). A contiguous section of each particle was also immunostained with AB765P (b,e,h,k) or 2B1.5 (c,f,i,l). Brown areas indicate the accumulation of collagens. The immunostaining with control IgGs showed negative results (data not shown). Note that the addition of PDGF-BB resulted in a large aggregate filled with cartilage matrix and COL2 (d,f,j,l). These results are representative of four independent experiments.