In vivo fluorescence-mediated tomography for quantification of urokinase receptor-dependent leukocyte trafficking in inflammation

Abstract

Background: Inflammation is characterized by leukocyte recruitment. Macrophages and neutrophils contribute to tissue damage and organ dysfunction. Modulating leukocyte invasion can protect fromthese adverse effects. Leukocyte recruitment criticallydepends on the urokinase-type plasminogen activator receptor (u-PAR). We here use a novel technique to longitudinally quantify cell trafficking in inflammatory models in live animals. Methods: Near-infrared fluorophore-labeled leukocytes were adoptively transferred to mice with thioglycollate peritonitis to study leukocyte trafficking to sites of inflammation. Macrophage andneutrophil trafficking was followed with three-dimensional fluorescence- mediated-tomography. u-PAR-/-and wild-type macrophage recruitment was studied by cross-over adoptive cell transfer to elucidate the role of leukocytic versusu-PARexpressed on other cells. Endotoxic shock-induced pulmonary inflammation was used to study u-PARs role for pulmonary neutrophil recruitment. Results: Mice experiencing peritonitis showed a significant increase in mean fluorescence intensity because of enhanced macrophage (315%, n=9-10),P<0.05) or neutrophil (194%, n=6, P < 0.02) recruitment. Fluorescence-mediated-tomography uncovered a macrophage recruitment defect in the peritonitis model for u-PAR-/- mice (147% of baseline) compared with control mice (335% of baseline, n=8-9, P<0.05).Whenu-PAR-/- macrophages were transferred to wild-type mice fluorescence intensity increased to 145% while wild-type macrophage transfer into u-PAR-/- resulted in 192% increase compared with baseline (n = 6, P < 0.05). Reduced neutrophil recruitment in pulmonary inflammation in u-PAR-/- mice was accompanied by improved pulmonary gas exchange. Conclusion: Using noninvasive in vivo fluorescence-mediated tomography to image leukocyte recruitment in inflammatory mouse models, we describe a novel macrophage recruitment defect in u-PAR-/-mice. Targeting u-PAR for modulation of leukocyte recruitment is a promising therapeutic strategy to ameliorate leukocyte induced tissue damage. Copyright © 2010, the American Society of Anesthesiologists, Inc.