Up-regulation of Pax5/BSAP and CD19 by BAFF. Human peripheral blood B cells were cultured with or without mitomycin-treated transfectants at a ratio of 10:2 in the presence or absence of SAC (0.0002% [wt/vol]) and IL-2 (50 U/mL). (A) After the treatment for 48 hours, the expression level of CD19, CD20, and CD21 was evaluated by FACS analysis. After treatment for 48 hours in the above conditions (A), cell lysates and nuclear extracts were prepared for immunoblot analysis using anti-Pax5 Ab (B) and EMSA using oligonucleotides containing Pax5 binding site (C), respectively. Lane 1, Pax5 oligonucleotide alone; lane 2, Pax5 mutant oligonucleotide alone; lane 3, B cell alone plus Pax5 oligonucleotides; lane 4, SAC/IL-2–stimulated B cells plus mock transfectants plus Pax5 oligonucleotides; lane 5, SAC/IL-2–stimulated B cells plus CD154 transfectants plus Pax5 oligonucleotides; lane 6, SAC/IL-2–stimulated B cells plus BAFF transfectants plus Pax5 oligonucleotides; lane 7, SAC/IL-2–stimulated B cells plus BAFF transfectants plus Pax5 mutant oligonucleotides; lane 8, SAC/IL-2–stimulated B cells plus BAFF transfectants plus Pax5 oligonucleotides plus competitor; lane 9, SAC/IL-2–stimulated B cells plus BAFF transfectants plus Pax5 oligonucleotides plus anti-Pax5 Ab. NS indicates nonspecific band. Data shown are representative of 3 different experiments.