Stimulated FAIM expression is preceded by induction of IRF4 expression in primary B cells. A, Primary B cells were stimulated by CD40L for 48 h alone (NS), or were stimulated by CD40L for 48 h during which time either anti-Ig, LPS, or IL-4 was added for the final number of hours indicated. From these cells, RNA was prepared, reverse transcribed, and evaluated for Faim and for Irf4 gene expression by real-time PCR. Expression levels were normalized to β2-microglobulin. Mean values for two independent experiments are shown, along with lines corresponding to the SEM. B, Primary B cells were stimulated by CD40L for 48 h alone (0 h), or were stimulated by CD40L for 48 h during which time anti-Ig was added for the final number of hours indicated. From these cells, lysates were prepared and evaluated for expression of FAIM-S and IRF4 by Western blotting. Blots were stripped and reprobed for tubulin content as a loading control. One of two comparable experiments is shown.