Overexpression of OPN in murine model of SLE induces B cell activation and IgG and IgM production, elevated autoantibodies (including anti-ds-DNA) levels and enhanced cytokine expression (TNF-α, IFN-γ and IL-1β) (Iizuka et al. 1998; Miyazaki et al. 2005; Weber and Cantor 2001; Wüthrich et al. 1998). Here, SPP1 is linked to systemic lupus erythematosus.