Receptor protein-tyrosine kinases (PTKs) are essential components of the signaling pathways required for cell-cell regulation. Many such pathways have been identified in various cell systems, but there has been little information on receptor PTKs in antigen-presenting cells (APCs) of the immune system. Lu and Lemke have identified three members of the same family of PTKs--Tyro, Axl and Mer--that are involved in regulating the function of APCs, including dendritic cells and macrophages. In mice genetically deficient in one, two, or three of these PTKs, an autoimmune phenotype developed with an increasing level of severity that correlated with an elevated activation status of APCs. These results suggest a direct link between this family of PTKs and the normal regulation of immune responses by APCs. See the Perspective by Schwartzberg.