Figure 4

CXCL4 in supernatants from activated platelets inhibits HIV-1. (A) The anti-HIV-1 factor(s) released from activated platelets are heat labile. Supernatants from activated platelets were left at RT or treated at 95°C for 15 minutes and used to inhibit infection of TZM-bl cells by HIV-1 NL4-3. The results of a representative experiment performed in triplicates are shown and were confirmed in 5 independent experiments, error bars indicate SD. (B) Recombinant CXCL4 inhibits HIV-1- and MLV-Env-driven host cell entry. Pseudotypes bearing the indicated Env proteins and normalized for comparable infectivity were used for infection of TZM-bl indicator cells in the presence and absence of recombinant CXCL4. β-galactosidase activities in cell lysates were quantified at 72 h post infection. The results of a representative experiment performed in triplicates are shown; error bars indicate SD. Comparable results were obtained in two independent experiments. (C) CXCL4 accounts for the anti-HIV-1 activity of platelet supernatants. Infectivity normalized pseudotypes were incubated with PBS, platelet supernatants or platelet supernatants preincubated with CXCL4-neutralizing antibody and infection of TZM-bl indicator cells was assessed. The results of a representative experiment are shown and were confirmed in two separate experiments. Infection by PBS treated viruses was set as 100%; error bars indicate SD.