Figure 4: IL-9 activates mast cells to produce IL-2.

MC-deficient C57BL6-Kit^W/W-v mice (six per group) were infected intranasally with live A. fumigatus conidia, engrafted intravenously with wild-type bone marrow-cultured mast cells (BMMC) or treated intraperitoneally with IL-2 for a week and assessed for (a) c-Kit⁺FcɛR⁺ lung mast cells (MC) and CD90.2⁺CD25⁺ lung ILC2 by flow cytometry (numbers refer to percentages of positive cells) with relative cell number and (b) IgE and cytokine production. (c) Lung histology (periodic acid–Schiff and Masson’s trichrome staining, in the insets); (d) cytokine production and (e) Th9-cell specific transcripts expression in Cftr^−/− mice infected as above and treated with imatinib intraperitoneally for a week. Photographs were taken with a high-resolution microscope (Olympus DP71) equipped with a × 20 objective, scale bars, 200 μm and a × 40 objective (insets of c, scale bars, 100 μm). Results are mean values±s.d., ELISA on lung homogenates for cytokines and PCR with reverse transcription on lung CD4⁺T cells. *P<0.05, **P<0.01, ***P<0.001, ****P<0.0001, MC-deficient C57BL6-Kit^W/W-v versus C57BL/6 mice or imatinib-treated versus untreated (none) mice (data represent pooled results or representative images from three experiments, Two-way ANOVA, Bonferroni post test). Irf4=interferon regulatory factor 4; Pu.1=purine-rich box 1.