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From the * Department of Medicine, We evaluated mature peripheral blood eosinophils for their expression of the surface tyrosine
kinase, c-kit, the receptor for the stromal cell-derived cytokine, stem cell factor (SCF). Cytofluorographic analysis revealed that c-kit was expressed on the purified peripheral blood eosinophils from 8 of 8 donors (4 nonatopic and 4 atopic) (mean channel fluorescence intensity 2.0- 3.6-fold, average 2.8 ± 0.6-fold, greater than the negative control). The uniform and selective
expression of c-kit by eosinophils was confirmed by immunohistochemical analysis of peripheral blood buffy coats. The functional integrity of c-kit was demonstrated by the capacity of
100 ng/ml (5 nM) of recombinant human (rh) SCF to increase eosinophil adhesion to 3, 10, and 30 µg/ml of immobilized FN40, a 40-kD chymotryptic fragment of plasma fibronectin, in
15 min by 7.7 ± 1.4-, 5.3 ± 3.3-, and 5.4 ± 0.2-fold, respectively, and their adhesion to 0.1, 0.5, and 1.0 µg/ml vascular cell adhesion molecule-1 (VCAM-1), by 12.7 ± 9.2-, 3.8 ± 2.5-, and
1.7 ± 0.6-fold, respectively. The SCF-stimulated adhesion occurred without concomitant changes
in surface integrin expression, thereby indicating an avidity-based mechanism. rhSCF (100 ng/ml,
5 nM) was comparable to rh eotaxin (200 ng/ml, 24 nM) in stimulating adhesion. Cell adhesion to FN40 was completely inhibited with antibodies against the
Department of Pathology, and § Department of Pediatrics,
Harvard Medical School, the
Division of Rheumatology, Immunology, and Allergy, and the
Department of Pathology, Brigham and Women's Hospital, Boston, Massachusetts 02115
4 and
1 integrin subunits,
revealing that the SCF/c-kit adhesion effect was mediated by a single integrin heterodimer,
very late antigen 4 (VLA-4). Thus, SCF represents a newly recognized stromal ligand for the activation of eosinophils for VLA-4-mediated adhesion, which could contribute to the exit of these
cells from the blood, their tissue localization, and their prominence in inflammatory lesions.
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