Analysis of neutrophil trafficking in a model of irritant dermatitis. (A) Croton oil was applied to either side of one ear and PBS was given to the contralateral ear of wild-type, CD18-null (CD18^−/−) and Mac-1–null (Mac-1^−/−) mice. After 6 hours, ear thickness was measured and recorded as the percentage increase in ear swelling of the irritant-exposed ear compared with that before the croton oil challenge. Histochemical analysis of cutaneous neutrophil infiltration by esterase staining of harvested ear specimens was also undertaken. Emigrated neutrophil counts (left panels) and ear edema (% increase) (right panels) are shown. Dotted line indicates average neutrophil counts in PBS-treated C57Bl/6 mice. *P < .005. (B) Wild-type, #85-Tg^hi, and #88-Tg^int were subjected to irritant dermatitis and analyzed as in panel A. Representative pictures of esterase-stained neutrophils (arrowheads) following induction of dermatitis in C57Bl/6 wild-type and #85-Tg^hi mice are shown. Scale bar represents 50 μm. All data are mean plus or minus SEM of n = 4 to 5 per group.