T cell independent secondary Env antibody responses after adoptive B cell transfer and stimulation with soluble gp130. BALB/c donor mice were immunized subcutaneously with 1 × 109 particles of Ad-SIV or as a control Ad-GFP. Six weeks later splenic B cells from both groups were transferred to nude mice resulting in SIV B cell recipient and control B cell recipient mice. At 4, 13 and 25 days after B cell transfer, SIV B cell recipient, control B cell recipient and Ad-SIV immunized donor mice were boosted i.v. with VLPs containing 300 ng of the gp140 ectodomain or with 300 ng of secreted gp130 SU. B cell recipient mice were also immunized s.c with Ad-SIV (109 particles, immunization of day 13 ommitted). IgG1 and IgG2a antibody levels to Env (A) and Gag (B) 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.