In Btk-deficient mice, the deposition of IC does not lead to tissue infiltration by neutrophils or vascular destruction. The Arthus reaction was elicited in the left ear of wild-type (wt) or Btk-deficient (Btk-ko) mice. (A) By measuring ear thickness, ear swelling was assessed as a parameter of edema and infiltration. Data presented are mean values of ear thickness (± SD). (B) After 8 hours, pictures of the treated ears of wild-type (wt) or Btk-deficient (Btk-ko) mice were taken for (C) the semiquantitative scoring of petechiae and hemorrhage as a marker of progressive, extensive vascular damage. (D) Eight hours after the Arthus reaction was elicited in wild-type (wt) and Btk-deficient (Btk-ko) mice, ears were harvested, embedded, and processed for immunofluorescence analyses. Slides were stained with anti–Gr-1-FITC, anti-CD31+anti-PE, and DAPI. Arrowheads indicate the position of neutrophils.