Cpa3-Cre; Mcl-1^fl/fl mice exhibit markedly reduced mast cell–dependent tissue swelling and leukocyte recruitment in IgE-dependent PCA. The data shown in panels A through C were pooled from the 3 independent experiments performed, each of which gave similar results. (A) Cpa3-Cre; Mcl-1^fl/fl mice (n = 9) and Cpa3-Cre; Mcl-1^+/+ control mice (n = 12) were sensitized by intradermal injection of 20 ng of anti-DNP IgE into the right ear pinna, with vehicle injection into the left ear pinna as a control. Mice were challenged by retro-orbital injection of 100 μg of DNP-HSA the next day. Ear swelling was measured at the indicated time points and data are shown as means ± SEM. **P < .01 and ***P < .001 versus corresponding values for Cpa3-Cre; Mcl-1^+/+ mice at the indicated time points. +P < .05, ++P < .01, and +++P < .001 versus corresponding values for contralateral vehicle control ears in mice of the same genotype at the indicated time points. P < .0001 by 2-way ANOVA for the swelling response in ears sensitized with anti-DNP IgE in Cpa3-Cre; Mcl-1^fl/fl versus Cpa3-Cre; Mcl-1^+/+mice. (B-C) Numbers of mast cells (B) and leukocytes (C) in the dermis of ear pinnae of Cpa3-Cre; Mcl-1^fl/fl mice (n = 9) and Cpa3-Cre; Mcl-1^+/+ control mice (n = 12) 6 hours after induction of PCA (IgE) or after in vehicle-treated control ears (vehicle). Data are shown as means + SEM for mast cells or leukocytes per millimeter of dermis. ***P < .001 versus corresponding values for Cpa3-Cre; Mcl-1^+/+ mice; +++P < .001 versus corresponding values for vehicle-treated mice in mice of the same genotype. (D) Giemsa staining to demonstrate mast cells (top, in 1-μm-thick, Epon-embedded sections) and H&E staining to demonstrate leukocytes (bottom, in 4-μm-thick, paraffin-embedded sections) in ear pinnae 6 hours after induction of PCA reactions. There are decreased numbers of mast cells (solid arrowheads in upper panels) and leukocytes (some indicated by solid arrows in lower panels) in sections from Cpa3-Cre; Mcl-1^fl/fl mice (right panels) versus Cpa3-Cre; Mcl-1^+/+ mice (left panels) subjected to PCA. Top: Some mast cells (*) exhibit alterations of the staining or location of many cytoplasmic granules, changes that are indicative of degranulation, whereas other mast cells (+) exhibit few or no granules exhibiting such changes. Bottom: Black arrows indicate leukocytes (primarily neutrophils). Insets depict selected mast cells exhibiting morphological evidence of extensive (*) or minimal or no (+) degranulation. Scale bars indicate 50 μm (for insets, scale bars indicate 5 μm); e indicates epidermis. Images were captured with an Olympus BX60 microscope with a 20× objective using a Retiga-2000R QImaging camera run by Image-Pro Plus Version 6.3 software (Media Cybernetics) and exported into Adobe Photoshop (CS3), in which images were white balanced and resized.