Analysis of the systematic immune response induced by Dermatophagoides pteronyssinus (Dp) + amorphous silica particles (SPs). 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. At 24 h after the last intradermal injection, splenocytes and plasma were collected from each group. Dp-specific IgG and its subclasses (A) in plasma were analyzed by ELISA. Splenocytes from each group were cultured with 100 μg ml-1 Dp. The levels of Dp-specific interferon (IFN)- γ and interleukin (IL)-4-producing cells were examined by individual cytokine-specific ELISPOT assay (B). A regression analysis of Dp-specific IL-4-producing cells was also performed (C). 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.