Similar binding of APRIL and BAFF to plasmablasts but preferential survival support mediated by APRIL. Recombinant trimeric murine molecules were tested for their capacity to (A) bind to PBs and (B) support the recovery of TT-specific ASCs. (A) Purified PBs (2 × 10⁵, isolated by CD138 staining) were incubated with 500 nM of a murine Flag-recombinant molecule (BAFF, APRIL A88, truncated APRIL H98, or control molecule [4–1BB-L]), with or without preincubation with heparin as indicated. The binding to PBs was revealed by antiflag staining. (B) Purified PBs were seeded into 96-well plates (5 × 10³ cells/well) in presence of different concentrations of recombinant murine molecules (complete APRIL A88, truncated APRIL H98, BAFF, or EDA-2 control molecule). TT-specific IgG ASCs were enumerated by ELISpot initially and after 48 hours of culture and survival expressed as mean (± SD) of 3 independent cultures. *P < .05 versus PB cultured with the same concentration of control molecule. **P < .05 versus PB cultured with the same concentration of BAFF. ***P < .05 versus PB cultured with same concentration of the truncated APRIL H98. (C) The expression of Bcl-X_L and Blimp-1 by PBs was evaluated by quantitative real-time reverse-transcription (RT)–PCR at onset (ex vivo) and after 24 hours of culture with 300 ng/mL of molecule. Results are expressed as the fold change of transcript expression for each condition of culture compared with t0 obtained from 1 representative experiment (pool of 10 mice) of 2.