YKL-40 is directly produced by giioma cells and reactive astrocytes. Confocal microscopy showed thatYKL-40 mRNA colocalizes with GFAP in both giiobiastoma (A-E) and tumor-induced non-neoplastic reactive astrocytosis (F-J). In contrast, although neurons adjacent to giioma are immunopositive for YKL-40, little mRNA is present (K-O). Admixed CD68-positive macrophages and microgiia likewise do not appear to produce YKL-40 mRNA in the neoplastic setting (P-T). Scale bars: A-E=50um; F-J, K-0 and P-T=20um. Insets are higher-magnification images of selected cells within each merged field. The first and second column images (A & B, F & G), K & L, P & Q) are 200× magnification.