| Therefore , to examine the potential role of Ku 70 in CSR , we generated K70T mice that carry a germline Ig HC locus in which the JH region was replaced with a functionally rearranged VH ( D ) JH and Ig lambda light chain transgene ( referred to as K70T / HL mice ) . ^^^ We conclude that Ku 70 is required for the generation of B cells that have undergone Ig HC class switching . ^^^ |