FCGR2B and systemic lupus erythematosus: Taken together these data all point in the same direction: the strong lupus-like phenotype of the FcγRIIb129-/- mice backcrossed more than seven generations into C57BL/6 background is caused by epistatic interaction between the Slamf129 locus, the C57BL/6 genome, and FcγRIIb−/− (Figure 2), similar to the epistatic interactions between FcγRIIbNZB (haplotype I), SlamfNZB (haplotype 2) and the C57BL/6 genome in C57BL/6 Nba2 congenic mice (114).