MECHANISMS OF ACUTE EOSINOPHIL MOBILIZATION FROM THE BONE-MARROW STIMULATED BY INTERLEUKIN-5 - THE ROLE OF SPECIFIC ADHESION MOLECULES AND PHOSPHATIDYLINOSITOL 3-KINASE

Mobilization of bone marrow eosinophils is a critical early step in th eir trafficking to the lung during allergic inflammatory reactions. We have shown previously that the cytokine interleukin (IL)-5, generated during an allergic inflammatory reaction in the guinea pig, acts syst emically to mobilize eosinophils from the bone marrow. Here, we have i nvestigated the mechanisms underlying this release process. Examinatio n by light and electron microscopy revealed the rapid migration of eos inophils from the hematopoietic compartment and across the bone marrow sinus endothelium in response to IL-5. Using an in situ perfusion sys tem of the guinea pig hind limb, we showed that IL-5 stimulated a dose -dependent selective release of eosinophils from the bone marrow. Eosi nophils released from the bone marrow in response to IL-5 expressed in creased levels of beta(2) integrin and a decrease in L-selectin, but n o change in or, integrin levels. A beta(2) integrin-blocking antibody markedly inhibited the mobilization of eosinophils from the bone marro w stimulated by IL-5. In contrast, an alpha(4) integrin blocking antib ody increased the rate of eosinophil mobilization induced by IL-5. In vitro we demonstrated that IL-5 stimulates the selective chemokinesis of bone marrow eosinophils, a process markedly inhibited by two struct urally distinct inhibitors of phosphatidylinositol 3-kinase, wortmanni n and LY294002. Wortmannin was also shown to block eosinophil release induced by IL-5 in the perfused bone marrow system. The parallel obser vations on the bone marrow eosinophil release process and responses in isolated eosinophils in vitro suggest that eosinophil chemokinesis is the driving force for release in vivo and that this release process i s regulated by alpha(4) and beta(2), integrins acting in opposite dire ctions.