Cell surface immunoglobulin expression on stimulated splenocytes. Splenocytes from wt (+/+), heterozygous (Δ/+), or homozygous (Δ/Δ) mice were cultured for 5 days with LPS+IL4 (to induce IgG1), LPS (to induce IgG3 and IgG2b), LPS+IFNγ (to induce IgG2a), or LPS+TGFβ (to induce IgA) and stained with anti-B220 and anti-isotype antibodies. The data shown are representative of 4 independent experiments for IgM, IgG1, IgG3, and IgG2b and of 2 independent experiments for IgG2a and IgA. Controls included staining with anti-B220 and anti-IgG1 for LPS stimulation and with anti-B220 and anti-IgG3 or anti-IgG2b for LPS+IL4 (not shown). Percentages of surface Ig–expressing cells among total B220-positive cells are shown in subpanels.