Fig 1: Protease expression in cells of leptomeningeal origin.(A,B) Protein expression of MMP9 and tPA in BMEN1 and HMC cells with neuroblastoma cells as a positive control47. (C–E) Expression of MMP9 in meningiomas. MMP9 expression in human meningeal tumors was determined by immunohistochemistry performed on low-grade meningiomas with a variety of morphologies. MMP9 was variably expressed in all meningiomas tested (n = 10), with greater expression in epithelioid than spindly tumors. Typical expression levels are seen in (C) levels in more epithelioid (D) and spindly (E) are also displayed. Vector Red was used as the chromogen in each panel. scale bar, 50 µM. (F–O) Expression of MMP9 and other markers in medulloblastoma-associated meninges. Meningeal surfaces adjacent to medulloblastomas were often difficult to identify by routine histologic stains (F), but could reliably be located with the use of anti-progesterone receptor, PR (G). Modest MMP9 expression was present in meningothelial cells at similar levels observed in meningiomas. More striking expression observed in the basal arachnoid and in the subjacent tumor (H). MMP9 expression here was comparable to that observed in areas of degenerating medulloblastoma with macrophage infiltration (not shown). However, CD68 immunostain demonstrated no macrophages, but only occasional tumoral microglia in these regions (I). Vimentin (J) and Collagen 4 (K) immunohistochemistry revealed increased tumor stroma in a submeningeal distribution within the medulloblastoma, but CD34 (L) and Factor VIII (M) immunohistochemistry did not demonstrate increased tumor vascularity in this region. Anti-CD61 immunostain for thrombocytes did not reveal hemorrhage or its reorganization as a source for MMP9 in this region (N) despite positive staining in thrombosed intratumoral vessels deeper elsewhere (O). Vector Red was used as chromogen in (C–E,H); all other immunohistochemical stains were developed using diaminobenzidine. Original magnification of all images was 200x. a, arachnoid cells. m, medulloblastoma tumor cells. scale bar, 100 µM.