Original article Selective upregulation of a functional b 7 integrin on differentiating eosinophils Background: The sequence of adhesion-molecule expression during eosinophil differentiation remains unclear. Methods: We analyzed the surface expression of a 4 , b 1 , and b 7 integrins and compared it to established myeloid developmental markers, using the eosinophilic cell line HL-60 clone 15, as well as cord and peripheral blood differentiation assays. Results: Cells induced to eosinophil differentiation by treatment with butyric acid, IL-5, and GM-CSF showed a signi®cant upregulation of b 7 integrin expression coincident with a marked upregulation of CD35 and attenuation of CD33 and b 1 integrin expression. In addition, adhesion of induced HL-60 clone 15 cells to ®bronectin was attenuated by a b 7 integrin antibody. Conclusions: Our data show that protein synthesis-dependent upregulation of the functional b 7 integrin occurs under conditions when a 4 and b 1 integrins are fully expressed, indicating a sequential appearance of speci®c adhesion molecules on differentiating eosinophil progenitors. J. Lundahl, R. Sehmi, L. Hayes, K. Howie, J. A. Denburg Department of Medicine, Division of Clinical Immunology and Allergy, McMaster University, Hamilton, ON, Canada Key words: adhesion molecules; ¯ow cytometry; hemopoiesis. Dr Judah A. Denburg Department of Medicine Room 3V46, Health Sciences Centre McMaster University 1200 Main St West Hamilton Ontario L8N 3Z5 Canada Accepted for publication 23 March 2000 To understand the role of eosinophils in allergic in¯ammatory diseases such as asthma, we must explore and understand the mechanisms that stimu- late the speci®c recruitment of these cells. The ingress of mature eosinophils from circulatory pools through speci®c upregulation of adhesion molecules and directional migration along a positive chemotactic gradient is a key part of the process of recruitment of these proin¯ammatory cells (1±3). In addition, we have proposed that a selective hemopoietic process, by which upregulation and release of bone-marrow- derived, eosinophil-lineage committed progenitors into the peripheral circulation occurs, increases the accessible pool of differentiating effector cells to the affected tissues (4, 5). Besides the action of soluble and membrane-bound cytokines, adequate hemopoiesis is dependent upon adhesive interactions between progenitors and the bone-marrow microenvironment, which provides a broad array of ligands, such as ®bronectin and vascular cell adhesion molecule (VCAM)-1 (6±10). In addition, several adhesion molecules contribute to bone-marrow-related adhesive interactions; namely, members of the b 1 and b 2 integrin families and the selectins. It has recently been demonstrated that expression of the b 1 integrin, the very late activation antigen (VLA)-4, and the b 2 integrin, lymphocyte function-associated antigen (LFA)-1, is lower on blood-derived progenitors than bone-marrow-derived progenitors (11, 12). In addition, in vivo administra- tion of anti-VLA-4 has been shown to mobilize progenitors into the peripheral circulation (13), and antibodies directed against its ligand, VCAM-1, disrupt the interaction between hemopoietic progeni- tor cells and bone-marrow stromal cells (14). From these observations, it is reasonable to propose that mobilization of progenitors and mature cells, from the bone marrow to the circulation, is at least in part, the result of changes in expression and/or function of adhesion molecules and the corresponding ligands, allowing an ordered, microenvironment-speci®c, pro- gression of hemopoiesis. In general, the pattern of expression of adhesion receptors on mature eosinophils is similar to that of other leukocytes, although eosinophils, unlike human neutrophils, express functional forms of VLA-4, VLA-6, and a 4 b 7 (15). Several studies have proposed that VLA-4/VCAM-1 and b 2 integrin/ICAM-1 adhe- sion pathways may be involved in the selective recruitment of eosinophils to sites of allergic in¯am- mation (15, 16). MAdCAM-1, the ligand for a 4 b 7 , and almost exclusively expressed on the gut epithe- lium, may be important in directing eosinophils to the intestinal walls, where they normally reside (17). The Allergy 2000: 55: 865±872 Printed in UK. All rights reserved Copyright # Munksgaard 2000 ALLERGY ISSN 0105-4538 865