IgE-dependent PSA is markedly reduced in Cpa3-Cre; Mcl-1^fl/fl mice.Cpa3-Cre; Mcl-1^fl/fl mice (n = 6) and Cpa3-Cre; Mcl-l^+/+ control mice (n = 6) were sensitized by IP injection of 20 ng of anti-DNP IgE. Mice were challenged by IP injection of 1 mg DNP-HSA the next day. Body temperature measured at the indicated time points is shown as mean ± SD. **P < .05; **P < .01; and ***P < .001 versus corresponding values for Cpa3-Cre; Mcl-1^+/+ mice at the indicated time points. P < .01 by 2-way ANOVA for the change in temperature in Cpa3-Cre; Mcl-l^fl/fl mice versus Cpa3-Cre; Mcl-l^+/+ mice. The data shown were pooled from the 2 independent experiments performed, each of which gave similar results. The death head symbols indicate when single mice in that group died.