Murine mast cell distribution in NOG mice. (A-D) Toluidine blue staining of the skin of NOG mice. Thin frozen sections from 12-week-old (A-B) and 20-week-old (C-D) NOG mice were stained with acidic toluidine blue. Arrows in the picture from 12-week-old NOG mice (A) indicate metachromatically stained cells. The upper dermis of 20-week-old NOG mice shows bandlike proliferation of toluidine blue⁺ cells and hyperplasia of epidermis. Magnification, × 200 (A,C) and × 400 (B,D). (E) Toluidine blue staining of mesentery of 20-week-old NOG mice, and arrows indicate mast cells. Magnification × 200. (F) Safranin-O staining of peritoneal cells obtained from 20-week-old NOG mice. Magnification, × 400. (G-K) Alcian blue and safranin-O staining in Carnoy fixed preparations from 20-week-old NOG mice. In lung, a few safranin⁺ CTMCs were recognized around major airways (H), whereas safranin-negative, Alcian blue⁺ MMCs were not observed in alveoli (G). In the gastric stomach, NOG mice showed safranin⁺ CTMCs in the submucosa (arrowheads in I and image with hypermagnification in J), and safranin-negative, Alcian blue⁺ MMCs in mucosa (arrows in I and image with hypermagnification in K). Magnification, × 100 (G,I), × 200 (H), and × 400 (J-K). (L-M) Toluidine blue staining of Carnoy fixed preparations from lymph node (L) and spleen (M) from 20-week-old NOG mice. Mast cells located only at the capsule of the lymph nodes. In the spleen, a few mast cells were present as shown with arrows in M. Magnification, × 200 (L-M).