h an autoimmune phenotype. In this regard, it is of note that hybrid strains between 129 and C57BL/6 mice, widely used in the generation of gene-targeted mice, are spontaneously predisposed to development of humoral autoimmunity with low levels of glomerulonephritis (Obata et al. 1979; Botto et al. 1998; Bickerstaff et al. 1999; Santiago-Raber et al. 2