Inhibition of infection with an anti-MHC antibody. Supernatant from HIV-1-producing 293T cells were passed through a 0.45 μm filter (Sarstedt). αMHC/VSV-G and αHEL/VSV-G HIV-1 samples were concentrated 100 times by centrifugation (25 kRPM at 4°C for 2 hours in a BeckmanCoulter ultracentrifuge) and were resuspended in 1% bovine serum albumine. 70% confluent target cells (293T cells) were treated with 1.0 μg/ml B9.12.2 mAb for 30 minutes prior to infection with concentrated αMHC/VSV-G or αHEL/VSV-G pseudotyped virions for 16 hours in the presence of 5 μg/ml polybrene. 48 hours later, EGFP positive clones (colony forming units (cfu)/ml) were counted. 100% transduction corresponds to the cfu obtained by the αMHC/VSV-G particles after pre-treatment of an isotype-matched antibody control. The results are representative of four independent experiments, and error bars indicate the standard error of the mean.