T cell independent secondary Env antibody responses after adoptive B cell transfer. 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 6, 11 and 41 days after B cell transfer, primed 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. 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 three animals per group are given. The shaded area indicates background antibody levels.