Strongly chemotactic for naive (L-selectinhi) CD4 T-cells and for CD8 T-cells and weakly attractive for resting B-cells and memory (L-selectinlo) CD4 T-cells. May play a role in promoting encounters between recirculating T-cells and dendritic cells and in the migration of activated B-cells into the T-zone of secondary lymphoid tissues. Binds to chemokine receptor CCR7. Binds to atypical chemokine receptor ACKR4 and mediates the recruitment of beta-arrestin (ARRB1/2) to ACKR4.