Syndecan-2 induces proliferation of B cells. (A) B220+ B cells from either wild-type (WT) or TACI knockout mice (KO) were cocultured with mitomycin C-treated Jurkat and Synd2/Jurkat cells at a ratio of 1:3 (105:3 × 105). Coculture conditions included 10 ng/mL IL-4, 1 μg/mL anti-IgM F(ab′)2, 100 ng/mL BAFF, 1 μg/mL anti-CD40L, alone or in combination. Cells were incubated for 5 days, at which time cultures were pulsed with 1 μCi (0.037 MBq) 3H-TdR for 18 hours before harvesting. Stimulation of both WT and TACI-KO B cells with IL-4 and αIgM with or without αCD40L, together with either parental Jurkat or Synd2/Jurkat cells, resulted in minimal proliferation. With the addition of BAFF, B-cell growth conditions became more optimal, and a significant increase in proliferation of WT B cells was seen in response to Synd2/Jurkat. TACI-KO B cells also proliferated at a higher rate in response to Synd2/Jurkat cells but considerably less than did WT B cells. Parental Jurkat and Synd2/Jurkat cells showed minimal proliferation after mitomycin C treatment (far right). (B) CD19+ cells from human donors were cocultured with irradiated pEAK12/Jurkat or Synd2/Jurkat cells. Coculture was performed in the presence of 100 ng/mL BAFF, 2 μg/mL anti-IgM F(ab′)2, 100 ng/mL IL-4, alone or in combination. Cells were pulsed with tritiated thymidine as in Panel A. In the absence of stimulation, or presence of BAFF, αIgM, or BAFF plus αIgM, B-cell growth is minimal in response to both pEAK12/Jurkat and Synd2/Jurkat cells. In the presence of IL-4, BAFF plus IL-4, or αIgM plus IL-4, B-cell growth increased significantly, particularly in response to Synd2/Jurkat cells.
