The Cpa3 promoter drives Cre expression in mast cells and basophils in vivo. (A-I) Expression of Cre in Cpa3-Cre mice, representative of similar results that were obtained in the 3 independent experiments performed. Fluorescence intensity plots depict GFP in cells from Cpa3-Cre; mT/mG mice (green solid lines) that express Cre, but not in mT/mG–only mice (red dashed lines) or Cpa3-Cre–only mice (gray filled curves). Percentage of GFP⁺ cells are indicated on the plots for Cpa3-Cre; mT/mG mice for each of the following cell populations: (A) peritoneal mast cells, (B) peritoneal macrophages, (C) splenic Ter119⁺ (erythroid) cells, (D) splenic basophils, (E) splenic eosinophils, (F) splenic neutrophils, (G) thymic T cells, (H) splenic T cells, and (I) splenic B cells.