Serum IL-6 levels are elevated in B6.Sle1.Yaa mice. The serum IL-6 levels of wild-type, B6.Sle1, B6.Yaa, and B6.Sle1.Yaa mice at the ages of 20 to 26 weeks are shown. The serum was obtained by cardiac puncture, and the levels of IL-6 were determined by ELISA. Results from 5 mice from each animal strain are shown as picograms per milliliter (mean ± SD). *P < .006 compared with the wild-type, B6.Sle1, and B6.Yaa mice.