• Huapeng Fan, Pam Hall, Leilani L Santos, Julia L Gregory, Gunter Fingerle-Rowson, Richard Bucala, Eric F Morand, and Michael J Hickey.
• Department of Medicine, Centre for Inflammatory Diseases, Monash University, Monash Medical Centre, Clayton, Victoria 3168, Australia.
• J. Immunol. 2011 Apr 15; 186 (8): 4915-24.

AbstractMacrophage migration inhibitory factor (MIF) promotes leukocyte recruitment to sites of inflammation. However, whether this stems from a direct effect on leukocyte migration is unknown. Furthermore, the role of the MIF-binding protein CD74 in this response has not been investigated. Therefore, the aim of this study was to examine the contributions of MIF and CD74 to chemokine-induced macrophage recruitment. Intravital microscopy studies demonstrated that CCL2-induced leukocyte adhesion and transmigration were reduced in MIF(-/-) and CD74(-/-) mice. MIF(-/-) and CD74(-/-) macrophages also exhibited reduced chemotaxis in vitro, although CD74(-/-) macrophages showed increased chemokinesis. Reduced CCL2-induced migration was associated with attenuated MAPK phosphorylation, RhoA GTPase activity, and actin polymerization in MIF(-/-) and CD74(-/-) macrophages. Furthermore, in MIF(-/-) macrophages, MAPK phosphatase-1 was expressed at elevated levels, providing a potential mechanism for the reduction in MAPK phosphorylation in MIF-deficient cells. No increase in MAPK phosphatase-1 expression was observed in CD74(-/-) macrophages. In in vivo experiments assessing the link between MIF and CD74, combined administration of MIF and CCL2 increased leukocyte adhesion in both MIF(-/-) and CD74(-/-) mice, showing that CD74 was not required for this MIF-induced response. Additionally, although leukocyte recruitment induced by administration of MIF alone was reduced in CD74(-/-) mice, consistent with a role for CD74 in leukocyte recruitment induced by MIF, MIF-treated CD74(-/-) mice displayed residual leukocyte recruitment. These data demonstrate that MIF and CD74 play previously unappreciated roles in CCL2-induced macrophage adhesion and migration, and they indicate that MIF and CD74 mediate this effect via both common and independent mechanisms.

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