RAG1 and cytomegalovirus infection: Major histocompatibility complex class I recognition receptor (Ly49I, Klra9) serves as an NK-cell activator48 and is involved in controlling cytomegalovirus infection.49 The reduction in receptors for NK-cell activation would explain the higher degree of lung carcinoma development in RAG1−/− Sgo1−/+ animals, because of reduced NK-cell-mediated surveillance for mutagenic CIN cells.