T cell independent secondary Env antibody responses after adoptive B cell transfer and stimulation with VLPs containing monomeric gp130 SU. BALB/c donor mice were immunized subcutaneously with 1 × 109 particles of Ad-SIV. Six weeks later, splenic B cells were transferred into nude mice resulting in SIV B cell recipient mice. At 4, 35 and 41 days after B cell transfer, SIV B cell recipient and Ad-SIV immunized donor mice were boosted i.v. with VLPs containing 300 ng gp140 ectodomain. B cell recipient mice were also immunized s.c with Ad-SIV (109 particles, immunization of day 35 omitted) or i.v. with VLPs containing 300 ng of membrane-anchored monomeric gp130 (gp130-VLPs). IgG1 and IgG2a antibody levels to Env and Gag were determined at the indicated time points after B cell transfer. The mean and standard deviation of four animals per group are given. The shaded area indicates background antibody levels.