Number of mast cells in skin tissues of WBB6F₁-W/W^v or WBB6F₁-tg/tgmice grafted to WBB6F₁-+/+ recipients. 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 value of skin graft from WBB6F₁-W/W^v mice.