P‐selectin requirement for neutrophil accumulation and injury in the direct passive Arthus reaction
The aim of this study was to investigate the role of P‐selectin in the accumulation of neutrophils in the direct passive Arthus reaction in rat skin. Direct passive Arthus dermal reaction was induced in male Sprague‐Dawley (SD) rats by a single i.v. injection of rat anti‐sheep globulin (SG) 1 h before i.d. injection of SG antigen. Anti‐P‐selectin or irrelevant control antibody was given 1 h before rat anti‐SG injection. Complement depletion was also performed in a separate group by pretreatment with cobra venom factor (CVF). In all groups dermal swelling was assessed 4 h after antigen challenge. Four hours after antigen challenge, rats treated with control antibody developed skin swelling (2.29 ± 0.47 mm), prominent complement deposition and neutrophil accumulation. This response was associated with local up‐regulation of endothelial P‐selectin. Pre‐treatment with anti‐P‐selectin antibody 1 h before passive Arthus induction prevented skin swelling (0.29 ± 0.06 mm, P < 0.05, cf with control antibody treatment), neutrophil accumulation and up‐regulation of endothelial P‐selectin despite complement deposition. CVF treatment prevented complement deposition, neutrophil accumulation and skin swelling (0.13 ± 0.07 mm, P < 0.05, cf with saline treatment). However, endothelial P‐selectin expression was still present. Inhibition of skin swelling and neutrophil accumulation in direct passive Arthus by functional inhibition of P‐selectin suggest a pivotal role for this adhesion molecule in this inflammatory process. These results also suggest that multiple steps are involved in the evolution of direct passive Arthus, including both P‐selectin expression and complement activation. However, while complement activation is essential for neutrophil accumulation and expression of dermal injury, P‐selectin up‐regulation initiated by antibody/antigen deposition occurs independently of complement activation.