Inactivation of chemotactic activity of Tat. Monoclonal antibodies against Tat (dilution 1:50) were mixed with Tat proteins, or Tat proteins were boiled for 10 minutes and then added to the lower compartment of the chamber. Tat-MBP and NH₂-Tat-GST were used in (A) and (B), respectively. Each protein was tested at the concentration of 20 ng/mL. Data are expressed as the number of migrated cells in 20 high-power fields. Columns, mean of 3 replicates (and representative of 1 out of 2 experiments done); bars, SD. *P< .001 compared with Tat-MBP without treatment, **P < .05 compared with NH₂-Tat-GST without treatment.