This very cool study by Dorothy P. Schafer, Emily K. Lehrman, Amanda G. Kautzman, Ryuta Koyama, Alan R. Mardinly, Ryo Yamasaki, Richard M. Ransohoff, Michael E. Greenberg, Ben A. Barres and Beth Stevens demonstrates how the immune system can participate in the circuitry of the developing mouse lateral genicular nucleus (LGN).