Platelets are required to seal vascular injuries inflicted by infiltrating leukocytes. (A) Immunostaining of the basement membrane of skin vessels before (left) and after (right) neutrophil transmigration had occurred during the cutaneous Arthus reaction in a rabbit. Adapted from Cochrane and Aikin68 with permission. (B-C) Representative photographs showing the aspect of the skin after 4 hours of cutaneous reverse passive Arthus reaction (B) or of the bronchoalveolar lavage fluid collected after 24 hours of LPS-induced lung inflammation (C), in control mice (100% platelets) and in mice that were immunodepleted for platelets alone (<3% platelets) or for platelets and neutrophils (neutrophil-depleted <3% platelets). Note that in both inflammatory models, neutrophil depletion before the reaction led to the prevention of inflammatory bleeding. (B) Adapted from Gros et al34 with permission. (C) Adapted from Hillgruber et al20 with permission. (D-E) Representative photographs showing that thrombocytopenic mice depleted for neutrophils or with defective neutrophil recruitment to the inflamed skin because of a genetic deficiency beta2 integrin (CD18−/−) are protected toward ultraviolet B radiation- or irritant contact dermatitis-induced petechial skin bleeding. Adapted from Hillgruber et al20 with permission.
