Number of mast cells in skin tissues of WBB6F₁-+/+ or WBB6F₁-tg/tgmice grafted to WBB6F₁-W/W^v mice. The bars represent the mean ± SE of 5 mice. In some cases, the SE was too small to be shown by bars. ^*P < .01 by t test when compared with the values of skin tissues grafted from WBB6F₁-+/+ mice.