Inhibition of X4, X4R5 and R5 tropic NL4-3 isolates by mHSA. (a) V3 loop amino acid sequences of NL4-3 mutants. NNT, recognition site for N-glycosylation. (b) TZM-bl cells were infected with virus supernatant representing an infectious dose of 500 foci/96-well. Infection was inhibited by adding mHSA (molar HSA:HOCl ratio 1:1000) to a final concentration of 1, 10, 50, 100 and 150 μg per ml of culture medium. Viral entry was monitored 2 days after infection by X-gal staining and counting of blue foci. Shown are the averages of triplicate wells. White symbols: X4 tropic viruses. Black symbols X4R5 (NL952) and R5 tropic viruses. The NL4-3 isolates were constructed by an exchange of the NL4-3 V3 loop against V3 loop sequences from primary isolates PI 952, PI-930, PI-918 and PI-991.