Analysis of Ig production in the sera and culture supernatants. (A) Ig production in unimmunized mice. Analysis of Ig secretion in 6-week-old mice was done by ELISA. Five wt mice and 6 Δ/Δ mice were analyzed. (B) ELISA analysis of Ig secretion after LPS or LPS+IL4 stimulation. Splenocytes from 5 wt (+/+), 7 heterozygous (Δ/+), and 6 homozygous (Δ/Δ) littermates were analyzed for LPS-induced IgM, IgG3, and IgG2b secretion and for LPS+IL4–induced IgG1 secretion.