JunB overexpression inhibits proliferation of mature peripheral B lymphocytes. (A) Spleens from Ubi-junB transgenic animals (JunB tg) and their littermate wild-type controls (wt) were used for MACS purification of T and B cells. Whole-spleen extracts (S), CD3-purified T lymphocytes (T), and CD19-purified B lymphocytes were subsequently subjected to Western blotting using an antibody directed against JunB. Extracts of wild-type and Ubi-junB transgenic fibroblasts were used as controls. (B) CD3⁺ T lymphocytes were MACS purified from spleens of Ubi-junB transgenic animals (n = 3; ▪) and their littermate wild-type controls (n = 3; □). Cells (2 × 10⁵/well) were subsequently subjected to a [³H]thymidine proliferation assay using increasing concentrations of concanavalin A. (C-D) CD19⁺ B-lymphoid cells were MACS sorted from spleen of wild-type (n = 3; □) and Ubi-junB transgenic (n = 3; ▪) mice. Cells (2 × 10⁵/well) were stimulated with the factors indicated for 48 hours and subjected to a [3H] thymidine incorporation assay. Co indicates control, cells that were plated in medium without the addition of growth factors. Data represent means ± SDs from 6 individual wells. One representative experiment is shown (n = 3).