The immune system and nervous system display striking similarities. Fernandis and Ganju discuss yet another example where a protein (Slit) originally identified for its role in modulating axon pathfinding is able to regulate immune cell migration. Slit isoforms expressed in the nervous system interact with members of the Robo receptor family to modify movement stimulated by the secreted attractants netrins and their receptors. In leukocytes, Slit 2 interacting with Robo receptors inhibits movement stimulated by the chemokine receptor (CXCR4). Fernandis and Ganju discuss the therapeutic potential of Slit as an antiviral agent and in the treatment of inflammatory diseases, autoimmune disorders, and cancer.