All animals were handled in strict accordance with good animal practice as defined by the French national charte on the ethics of animal experimentation. Animal work was approved by the Regional ethical committee (Comité Régional d'Ethique pour l'Experimentation Animal de la Région Rhone-Alpes, CREEA, protocol Nu 220) and experiments were performed in the INSERM Jean Mérieux BSL-4 laboratory in Lyon, France (French Animal regulation comittée Nu A69 387 05 02).