Rapid halt of the clearance of opsonized red blood cells (RBCs) by liposomal clodronate.

(A) Pretreatment with liposomal clodronate prevents the clearance of opsonized, circulating RBCs. Mice were injected with either PBS- or clodronate-containing liposomes. At 36 hours later, they were injected with identical numbers (10⁹) of CFSE-labeled RBCs with or without in vitro incubation with anti-RBC antibody (Ter-119). Clearance of labeled RBCs from peripheral circulation was assessed by flow cytometry of blood specimens obtained at the indicated times. Data are expressed as percentages of circulating RBCs that are CFSE⁺ (± standard errors). Data presented are from 1 experiment representative of 2. (B) Liposomal clodronate acts extremely rapidly to halt clearance of opsonized RBCs. Mice were injected with liposomal clodronate either simultaneously or prior to (at the time indicated) injection with CFSE-labeled/antibody-opsonized RBCs (5 × 10⁸). Control mice were injected either with an identical number of nonopsonized RBCs (and no liposomes) or with PBS liposomes (and opsonized RBCs). Clearance of labeled RBCs from peripheral circulation was assessed by flow cytometry of whole blood, obtained 4 hours after RBC injection. Data presented are from 1 experiment representative of 3; data are presented ± standard error.