BLyS induces both Pim 1 and Pim 2. Purified small resting B cells were cultured for 2 days unstimulated or with 100 ng/mL rhuBLyS, 5 μg/mL anti-Ig or 0.5 μg/mL anti-CD40. Lysates from the freshly isolated input population (*) and after 24 and 48 hours of culture were prepared and analyzed by Western blot. Results are representative of 4 independent experiments and show the 2 isoforms of Pim1 at 33 and 44 kDa, and the 3 isoforms of Pim 2 at 34, 37, and 40 kDa. Relative protein levels of each Pim isoform were determined by densitometry and normalized to the unstimulated B-cell population cultured for 24 hours as described in Figure 2C.