Representative histologic sections of murine skin after tick infestation or suture placement.

(A) Marked purulent inflammation induced by 24 hours of suture placement in a CD11b^−/− mouse. Arrow indicates hole in dermis where suture used to be. Arrowhead indicates neutrophilic inflammation. (B) Complete absence of neutrophilic response to suture in a CD18^−/− mouse. Arrow indicates retained suture. (C) Minimal, primarily lymphocytic inflammation induced by 24 hours of tick feeding in a CD11b^−/− mouse. Arrow indicates I scapularis mouth parts embedded in the dermis. Arrowhead indicates pink cement substance secreted by the tick to aid in firm attachment. Narrow, concave arrow indicates venules containing erythrocytes and nonextravasated leukocytes. (D) Minimal inflammation induced by 24 hours of tick feeding in a B6 mouse. Arrow indicates I scapularis mouth parts breaching the superficial epidermis. (E) Moderate hemorrhage induced after 72 hours of tick feeding in a B6 mouse. Arrow indicates remnants of I scapularis near epidermis. Arrowheads indicate hemorrhage and disruption of normal dermal tissue architecture. Note minimal leukocytic inflammation compared with abundant hemorrhage. (F) Moderate hemorrhage induced after 72 hours of tick feeding in a CD11a^−/− mouse. Arrows indicate pools of hemorrhage and free erythrocytes dissecting up through muscle layer of dermis.