Tat tethered to the surface of Namalwa cells or of endothelium promotes lymphoid cell trans-endothelial migration. Namalwa cells (A) or HACEC monolayers (B) were left untreated or pretreated with heparinase III and/or preincubated with s-Tat (550 nM). After washing with PBS or PBS/NaCl, Namalwa cells were assayed for migration across HACEC monolayer in response to CXCL12 (25 nM). Alternatively, SYN-NCs were subjected to the PBS/NaCl wash before preincubation with s-Tat and assayed for transmigration (). Each point is the mean ± SEM of 2 or 3 duplicate determinations.