Runx1^P1N/P1N mice have markedly reduced basophil- and IgE-dependent chronic allergic inflammation. (A) WT (■) or Runx1^P1N/P1N mice (○) were sensitized passively by an IV injection of TNP-specific IgE 1 day before being challenged with an intradermal injection of TNP-OVA into the left ear pinna and OVA into the right ear pinna as a control. Ear swelling at each time point is shown (means + SEM, n = 3 each). (B) Immunohistochemical staining with an anti-mMCP8 Ab (DAB substrate) to visualize basophils (some indicated with solid arrowheads) and Giemsa counterstaining (4-μm-thick, paraffin-embedded sections) to demonstrate leukocytes in ear pinnae from WT or Runx1^P1N/P1N mice 4 days after challenge with OVA or TNP-OVA. Scale bars indicate 100 μm (top panel) or 25 μm (bottom panel). Data shown are from 1 of 2 independent experiments, each of which gave similar results. ***P < .0001; **P < .001; no asterisk, P > .05 relative to the corresponding WT mice.