Increased proliferation of T cells and survival of T cells from APRIL Tg mice in vitro. (a) Increased proliferation of Tg T cells after 2 days’ culturing with anti-CD3 alone, or anti-CD3 in combination with anti-CD28. (b) T cell response in APRIL Tg mice in vivo: Delayed deletion of superantigen-responsive Vβ8⁺ CD4⁺ cells in APRIL Tg mice. PBLs were stained for CD4, CD8, and Vβ8 on the days indicated (n = 4). This is one representative experiment of four performed. ANOVA confirmed that the differences for CD4⁺ cells at days 7, 10, and 13 are statistically significant (Table 2). *P < 0.05. The Vβ6⁺ subpopulation of CD4⁺ and CD8⁺ cells was unresponsive at all time points analyzed (not shown). (c and d) Survival of purified T cells cultured for 3 days alone, with anti-CD3, or with anti-CD3 plus anti-CD28. Cells were stained for CD4 (c) or CD8 (d) and PI as described in Methods. (e) Purified T cells of C57BL/6 mice were cultured for 2 days without stimulation, alone or in the presence of 5 μg/ml recombinant APRIL, and PI-stained. (f) Purified CD4⁺ T cells were cultured for 3 days without stimulation, alone or in the presence of 50 μg/ml of TACI-Fc, BMCA-Fc, or control Ig. Similar results were obtained for CD8⁺ T cells. All data in a and c–f are the mean ± SD of triplicate determinations of a representative experiment of at least three performed. The statistical significance of the data was determined using ANOVA.