Loss of p85β regulatory subunit in mice results in increased number of mast cells in vivo. (A) Cells from the peritoneal cavity of WT and p85β-deficient mice were harvested and stained with antibodies against KIT and IgE receptor. Representative dot blots indicate peritoneal cavity-derived mast cells stained with anti-KIT and anti-IgE receptor antibodies from the indicated genotypes. Numbers in the upper right quadrant of dot blot indicate the percentage of peritoneal cells that are double-positive for KIT and IgE receptor expression. (B) Bar graph represents quantitative assessment of the total number of mast cells in 5 mL of peritoneal lavage from the indicated genotypes. n = 4 (mean ± SEM). *P < .05, WT versus P85α^−/−. **P < .05, WT versus P85β^−/−. (C) Representative photomicrographs of toludine blue-stained tissue sections derived from WT, P85α^−/−, and P85β^−/− mice. (D) Bar graph represents quantitative assessment of toludine blue-positive mast cells in the indicated tissues. n = 3 to 5 (mean ± SEM). *P < .05. (E) Histologic analysis of stomach and spleen showing the reconstitution of mast cells in W^sh mice. P85α^−/− mice were injected intraperitoneally with 5-flurouracil (150 mg/kg body weight), and BM cells were harvested after 72 hours of injection. These cells were transduced with p85α or p85β and sorted to homogeneity on the basis of EGFP expression. Sorted cells (1 × 10⁶) were mixed with recipient W^sh splenocytes (0.1 × 10⁶ cells) and injected into mast cell-deficient W^sh mice. After 4 months of transplantation, mice were killed; different tissues were harvested and analyzed for mast cells by leader staining. Shown are representative sections of spleen and stomach from the indicated genotypes. Arrows indicate mast cells in various tissues.