Haploid loss of ID4 in TCL1-tg B cells inhibits dexamethasone-mediated apoptosis in vitro and promotes TLR9 agonist-stimulated cell proliferation in vivo. (A) CD19⁺ cells were isolated from the spleens of 1-month-old Eμ-TCL1-tg mice with or without haploid loss of ID4. Isolated cells were cultured in hybridoma medium supplemented with 1% β-mercaptoethanol. After 24 hours of treatment with 1μM dexamethasone, cells were analyzed by annexin/PI flow cytometry. P value is determined on the basis of a 2-sample t test. (B) Three mice from both groups were injected with CpG oligonucleotide every 4 days for a total of 7 injections. Four days after the last injection, BrdU was injected daily for another 4 days, and CD19⁺ cells were isolated. The total number of CD19⁺BrdU⁺ cells was then determined by flow cytometry. P value is based on a 2-sample t test.