FIGURE 4.

IRF4 plays a nonredundant role in up-regulating FAIM expression. Follicular B cells from IRF4-null mice and from littermate control mice were sort-purified as described in Materials and Methods and then harvested before stimulation, or were stimulated and then harvested. Follicular B cells were >95% pure upon postsort reanalysis. A, B cells were stimulated by CD40L for 48 h alone (CD40L) or they were stimulated by CD40L for 48 h, during which time anti-Ig was added for the final 6 h of culture. RNA was prepared, reverse transcribed, and evaluated for Faim gene expression by real-time PCR. Faim expression was normalized to expression of β₂-microglobulin. Mean values for three independent experiments are shown, along with lines corresponding to the SEM. B, Sort-purified B cells from IRF4-null and from littermate control mice were unstimulated or were stimulated by anti-Ig for 2 or 10 min. B cell lysates were prepared and evaluated for expression of phosphorylated proteins by Western blotting with 4G10 anti-phosphotyrosine Ab. Blots were reprobed for expression of actin as a loading control.