ORIGINAL ARTICLE Evidence for a regulatory role of a4 – integrins in the maturation of eosinophils generated from the bone marrow in the presence of dexamethasone M. I. Gaspar-Elsas à , T. Queto à , Z. Vasconcelos à , C. P. Jones w , J. Lannes-Vieira z and P. Xavier-Elsas w à Department of Paediatrics, Instituto Fernandes Figueira, FIOCRUZ, Rio de Janeiro, Brazil, w Department of Immunology, Instituto de Microbiologia Prof. Paulo de G ´ oes, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil and z Laborat ´ orio de Biologia das Interac ¸o˜es, Instituto Oswaldo Cruz, FIOCRUZ, Rio de Janeiro Clinical & Experimental Allergy Correspondence: P. Xavier-Elsas, MD PhD, Department of Immunology, Instituto de Microbiologia Prof. Paulo de G ´ oes, Universidade Federal do Rio de Janeiro, CCS Bloco I, room I-2-066, Cidade Universit´ aria, CEP 21941-590 Rio de Janeiro, Brazil. E-mail: pxelsas@gmail.com Cite this as: M. I. Gaspar-Elsas, T. Queto, Z. Vasconcelos, C. P. Jones, J. Lannes- Vieira and P. Xavier-Elsas, Clinical & Experimental Allergy , 2009 (39) 1187–1198. Summary Background Although eosinophils co-express multiple integrin receptors, the contributions of integrins to eosinophil development have not been explored. We previously described extensive aggregation and cytological immaturity in eosinophils developing in bone-marrow (BM) cultures exposed to dexamethasone. Here we examined the relationship of a4 integrins with these effects of dexamethasone. Objectives We evaluated: (a) the effects of exposure to dexamethasone in BM culture on eosinophil expression of a4 integrin receptors and ligands; (b) the contribution of a4 integrins to eosinophil aggregation and maturation. Methods Cultures were established with IL-5 (alone or with dexamethasone) for up to 7 days, and eosinophil production, a4 integrin receptor/ligand expression, aggregation and morphology were evaluated before and after targeting a4 integrin-dependent adhesions. Because prostaglandin E2 (PGE2) modifies the effects of dexamethasone on eosinophilopoiesis, PGE2 effects on a4 integrin expression and function were also evaluated. Results Dexamethasone increased the yield of eosinophils up to day 7. The frequency of eosinophils expressing a4, b1 and b7 integrin receptors at day 7 was also increased by dexamethasone. Eosinophils also expressed the a4b1 ligand, VCAM-1. Dexamethasone increased the expression of a4 integrin and VCAM-1 in aggregates containing eosinophils as early as day 3. PGE2, added up to day 3, modified the effects of dexamethasone to suppress the expression of a4 integrin, decrease aggregation and promote cytological maturation of eosinophils recovered at day 7. Dissociation of immature eosinophils from clusters present at day 3 by reagents targeting a4 or b1 integrins or VCAM-1 also induced cytological maturation. The concordant effects of targeting a4 integrins with drugs and antibodies support a relationship between a4-mediated aggregation and maturational arrest. Conclusions These observations support a novel role for a4 integrin receptors and ligands in eosinophilopoiesis. In addition, increased a4 expression following glucocorticoid exposure may contribute to the retention and accumulation of eosinophils in haemopoietic tissue. Keywords adhesion molecules, bone marrow, eosinophils, glucocorticoids, prostaglandin Submitted 4 August 2008; revised 19 April 2009; accepted 21 April 2009 Introduction Mature eosinophils, prominent in allergic inflammation [1], are highly sensitive to glucocorticoids, which induce eosinopenia and accelerate apoptosis [2, 3]. However, the effects of glucocorticoids on earlier stages of eosinophil development are more complex, as they decrease IL-5 production [4], but paradoxically enhance the responses of eosinophil precursors to IL-5 [5, 6]. As a result, eosinophils developing in bone-marrow (BM) culture are protected by dexamethasone [7] from apoptosis [both spontaneous and induced by exogenous ligands such as Basic Mechanisms in Allergic Disease doi: 10.1111/j.1365-2222.2009.03289.x Clinical & Experimental Allergy, 39, 1187–1198  c 2009 Blackwell Publishing Ltd