Effects of amorphous silica nanoparticles (nSPs) on atopic dermatitis (AD)-like skin lesions induced by Dermatophagoides pteronyssinus (Dp). NC/Nga mice were intradermally injected on the ventral side of both ears with Dp alone or Dp plus SPs in PBS on days 1, 3, 5, 7, 9, 11, 13, 16, and 18. Ear thickness was measured on days 0 and 19 (A). The ears were removed 24 h after the last intradermal injection. Sections were prepared, and the ears were stained with H&E to assess representative symptoms of AD (B and C) or with toluidine blue to assess mast cell infiltration (D and E). Representative histological findings of the PBS, Dp, Dp + mSP1000, and Dp + nSP30 groups are shown. Several representative symptoms of AD were scored in the H&E sections (C). Infiltration of mast cells was evaluated as the number of cells in toluidine blue sections in a high power field (E). Data are presented as mean ± SE of 4-5 animals per group. The results are representative of two separate experiments. *P < 0.05 vs. Dp group. Scale bars: 100 μm (B) and 50 μm (D).