Previous studies of Slamf1-/- [21] and Slamf6-/- [19] mice that were backcrossed to C57Bl/6 mice have used lupus-prone (129 x B6) Sle1b mice as WT controls, due to residual 129-derived sequences around the SLAM loci, which were mutated in 129 ES cells. This evidence concerns the gene SLAMF1 and systemic lupus erythematosus.