A role of Syk in the acute inflammatory response. The reverse-passive Arthus reaction was induced in the left ear of Syk^+/– and Syk^–/– bone marrow chimeric mice for 6 hours. (A) Gr-1 staining of PMNs (arrow) in histologic sections of the left ear. (B) PMN extravasation was determined by counting Gr-1⁺ cells within 6 hours after treatment in 5 different microscopic fields of every section. (C) Edema formation was measured as ear swelling 6 hours after treatment. (D) Semiquantitative score for hemorrhage 6 hours after treatment. n = 4 (Syk^+/– animals); n = 3 (Syk^–/– animals). Means ± SD are shown. **P < .002; ***P < .001.