Lyn-mediated functional association between chemokine receptors and β₂ integrins modifies the process of adhesion/de-adhesion through chemokine-regulated cell motility. SDF-1 activation of the chemokine receptor CXCR4, through the G_α subunit (A) induces activity of the Src-kinase Lyn (B). Activation of Lyn kinase results in diminished β₂ integrin affinity for ICAM-1, promoting movement (B). In the absence of Lyn or SDF-1, which initiates Lyn activation (C), ICAM-1–mediated adhesion is favored, and ability of cells to migrate is decreased (D). Therefore, by regulating the ability of hematopoietic cells to roll on or attach to stromal cells, Lyn plays a role in the regulation of the interaction between cells of these types.