Effects of pentosan polysulfate on proteoglycan, collagen type I and collagen type II deposition in pellet cultures. Photomicrographs of sections of mesenchymal precursor stem cell (MPC) pellet cultures showing the effects of pentosan polysulfate (PPS) on chondrocyte development. Representative 5 μm serial tissue sections are shown of cells cultured as pellets for 10 days in (a) the absence of PPS (top nine panels) or (b) the presence of PPS (bottom nine panels). Control pellet sections (a) appeared fragmented with less intense toluidine blue staining for proteoglycans in comparison with those pellet cultures treated with 2.5 mg/ml PPS (b). Immunohistochemical staining confirmed higher levels of the cartilage matrix protein and collagen type II, and lesser levels of collagen type I in pellet cultures treated with 2.5 μg/ml PPS (b) than in the corresponding control pellet cultures (a).