Expression of human Kit as detected by APAAP (A through C) and tumor histopathology (D through H). The red color shown in the photographs in (A through C) indicates the presence of human Kit protein detected with IDC3 antibody on parental MTHC (A), WTKit-expressing MTHC (B), and V816Kit-expressing MTHC (C). The parental cells do not express human c-Kit and, therefore, (A) represents a negative control. The bar in (C) represents 15 μm and provides the scale for (A, B, and C). The right panel shows photographs of tumor sections. Photographs (D, E, and F ) show hematoxylin and eosin staining of a paraffin-embedded tumor section and (G and H) show esterase expression in frozen sections. (D) Shows a region through the center of the vascularized tumor, (E and F ) show invasion of the tumor cells into surrounding fat tissue and a blood vessel, respectively. (G and H) Show regions of staining for predominantly macrophage or neutrophil esterase, respectively. The arrows in photograph (G) indicate the larger cells showing phagocytosis of other cells. The bar in (D) represents 38 μm and provides the scale for (D) through (H).