Homodimerization of Tat is required to mediate Namalwa cell adhesion to the endothelium. (A) Aliquots (5 μg) of the indicated recombinant forms of GST-Tat were analyzed in nonreducing 12% sodium dodecyl sulfate–polyacrylamide gel electrophoresis and visualized by blue Coomassie staining. ◀ and ◁ point to the 72-kDa homodimer and to the monomeric form of Tat, respectively. (Top of panel) Percentage of Tat that underwent dimerization as calculated by densitometric measurement of the bands. (B) Overlay of blank-subtracted sensograms showing the binding of the indicated proteins (500 nM) injected over a BIAcore sensor chip coated with s-Tat. The SPR signal was expressed in terms of resonance units (RU). (C) SYN-NCs were allowed to adhere to plastic coated with the indicated proteins (550 nM). Then, adherent lymphocytes were counted. Each point is the mean ± SEM of 3 to 8 duplicate determinations. (D) GM7373 EC monolayers were preincubated without (−) or with the indicated proteins (550 nM), washed to remove unbound proteins, and assayed for their capacity to promote SYN-NC adhesion.