CD40LG and systemic lupus erythematosus: Moreover, B6.Sle1 mice which carry the sle 1 risk locus from NZM mice produce more antigen-specific IgG and total IgG and exhibit enhanced IgM to IgG class switching (Rahman et al. 2007), suggesting that part of the genetic risk for SLE may include a propensity to high IgG levels.