Leukocyte adherence contributes to disruption of the blood–brain barrier during activation of mast cells

Abstract

The goal of this study was to examine the role of leukocytes in disruption of the blood–brain barrier during activation of mast cells using compound 48/80. We examined the pial microcirculation in rats using intravital fluorescence microscopy. Permeability of the blood–brain barrier (clearance of fluorescent-labeled dextran; molecular weight 10 000 daltons; FITC-dextran-10 K) was determined while suffusing with vehicle or compound 48/80 (10 or 25 μg/ml). During superfusion with vehicle (saline), clearance of FITC-dextran-10 K from pial vessels was modest and remained relatively constant during the experimental period (0.52±0.05 ml/s×10 −6 at 80 min). In addition, diameter of pial arterioles remained constant (32±5 μm) while suffusing with vehicle. In contrast, topical application of compound 48/80 produced marked disruption of the blood–brain barrier to FITC-dextran-10 K. For example, suffusion with compound 48/80 (25 μg/ml) increased clearance of FITC-dextran-10 K about 4-fold to 2.26±0.25 ml/s×10 −6 at 80 min. In addition, superfusion with compound 48/80 (25 μg/ml) constricted pial arterioles by 26±9% at 80 min. To determine a potential role for leukocyte adhesion to endothelium in disruption of the blood–brain barrier during suffusion with compound 48/80, we examined permeability during suffusion with compound 48/80 (25 μg/ml) in the presence of WT.3 (2 mg/kg i.v.), a monoclonal antibody directed against the functional epitope of the leukocyte adhesive glycoprotein (CD18; LFA-1β). We found that infusion of WT.3 markedly attenuated disruption of the blood–brain barrier to FITC-dextran-10 K in response to compound 48/80. The clearance of FITC-dextran-10 K during superfusion with compound 48/80 in the presence of WT.3 was 1.29±0.14 ml/s×10 −6 at 80 min ( P<0.05). Thus, the findings of the present study suggest that application of compound 48/80, to degranulate mast cells, activates the adhesion of leukocytes to cerebral venular endothelium which contributes to disruption of the blood–brain barrier.