Human skin mast cells express functional β₁ integrins that mediate adhesion to extracellular matrix proteins

We have evaluated the adhesion of human cutaneous mast cells to several components of the extracellular matrix (plasma fibronectin, laminin, collagen type I and IV) and studied whether these cells express the β₁ integrins potentially involved in the adhesion to these proteins. Human skin mast cells (5.1 ± 1.5% pure) spontaneously adhered to fibronectin and laminin (0.1 to 10 μg/ml) immobilized on plastic surfaces (e.g., 14 ± 7.2% and 14 ± 4.4% adhesion at 10 μg/ml, respectively). Similar results were obtained with a 90% pure mast cell preparation. In contrast, cutaneous mast cells did not adhere to collagen type I (1.6 ± 0.5% adhesion) or type IV (1.2 ± 0.8% adhesion). Control adhesion in BSA-coated wells was <5%. Mast cell adhesion to fibronectin was optimal after an incubation period of 60 to 90 min (t( 1/2 ) = 28.2 ± 6.2 min), whereas adhesion to laminin was faster (t( 1/2 ) = 10.1 ± 1.2 min), being nearly optimal after a 15-min incubation period. Human skin mast cell adhesion to fibronectin and laminin was found to be dependent on the presence of divalent cations in the extracellular medium. Dual-color immunofluorescence and flow cytometry were used to evaluate whether human skin mast cells (51.3 ± 3.9% pure) express β₁ integrins that may mediate cell adhesion to extracellular matrix proteins. These mast cells were found to express VLA (very late Ag)-3 (75.3 ± 35.6 specific fluorescence intensity) and, to lesser degree, VLA-4 and VLA-5 receptors (8.0 ± 2.5 and 6.9 ± 3.2 specific fluorescence intensity, respectively). In contrast, VLA- 1, VLA-2, and VLA-6 integrins were not expressed significantly. mAb to VLA- 3, VLA-4, and VLA-5 each inhibited by 70% skin mast cell adhesion to fibronectin. mAb to VLA-3 nearly abolished mast cells adhesion to laminin, whereas anti-VLA-4 and anti-VLA-5 were ineffective. Finally, immunosuppressant cyclosporin A (100 nM) and FK-506 (10 nM) significantly inhibited mast cell adhesion to both fibronectin and laminin (p < 0.05). Our data demonstrate that human skin mast cells spontaneously adhere to fibronectin and laminin, and that this adhesion is mediated by VLA-3, VLA-4, and/or VLA-5 integrins on these cells. Interactions between these β₁ integrins and extracellular matrix proteins may be involved in perivascular tissue localization of human mast cells in vivo.