Circulating platelet–leukocyte complexes are increased in allergen-sensitized mice after allergen exposure. Sham- and OVA-sensitized mice were exposed to allergen, and circulating blood was obtained by cardiac puncture 24 hours after 1 day of allergen exposure. In some groups, mice were rendered thrombocytopenic by the administration of busulfan. Selected groups of thrombocytopenic mice were intravenously administered WPs, FUSPs, or FSPs. Leukocytes (detected by their forward and side scatter characteristics) attached to platelets were identified by anti–CD41-FITC fluorescence. n = 5-9 animals per group. Data are expressed as mean ± SEM. ^*P < .05; ^***P < .001.