Mice. BALB/c mice (Charles River Laboratories, http://www.criver. com/) were purchased for use in these studies. C.B6-Klra8 Cmv1-r /UwaJ, referred to as Klra8, (Jackson Laboratory, http://www.jax.org/), B10.D2, and B10.D2-DAP12-deficient (DAP128) animals were bred in pathogen-free breeding facilities at the Centre d'Immunologie de Marseille-Luminy (Marseille, France). Experiments were conducted in accordance with institutional guidelines for animal care and use. Protocols have been approved by the French Provence ethical committee (number 04/2005) and the US Office of Laboratory Animal Welfare (assurance A5665-01).