T-cell adhesion induced by proteoglycan-immobilized cytokine MIP-lβ

Abstract

LYMPHOCYTE migration from blood into tissue depends on integrin-mediated adhesion to endothelium^1–4. Adhesion requires not only integrin ligands on the endothelium, but also activation signals because T-cell integrins cannot bind well until they are activated. The physiological 'triggers' for T-cell adhesion are unknown, but cytokines may be good candidates as they are released during inflammation and trigger adhesion in neutrophils and monocytes^2,5,6. We have identified a cytokine, macrophage inflammatory protein-1β (MIP-1β), that induces both chemotaxis and adhesion of T cells; MIP-1β is most effective at augmenting adhesion of CD8⁺ T cells to the vascular cell adhesion molecule VCAM-1. We reasoned that, as cytokines in vivo will be rapidly washed away, MIP-1β might be bound to endothelial surfaces and so induce adhesion in its immobilized form. Here we show that: (1) M IP-1β is present on lymph node endothelium; (2) immobilized MIP-1β induces binding of T cells to VCAM-1 in vitro. M IP-1β was immobilized by binding to proteoglycan: a conjugate of heparin with bovine serum albumin and cellular proteoglycan CD44 were both effective. We propose that MIP-1β and other cytokines with glycosaminoglycan-binding sites will bind to and be presented by endothelial proteoglycans to trigger adhesion selectively not only of lymphocyte subsets, but also of other cell types.