The HIV enhancing activity of individual SE samples correlates with SEVI concentrations. (A) Enhancement of HIV-1 infection by SE samples from 14 different donors. R5 HIV-1 stocks were mixed with 10% (v/v) of the SE samples or PBS and used for infection of TZM-bl indicator cells. Similar results were obtained using SE samples from more than 80 additional donors. Reactivity of anti-SEVI-antiserum from guinea pigs to (B) the indicated monomeric peptides or IVES, a peptide containing the reverse amino acid sequence of PAP248-286 and full-length PAP. (C) SEVI fibrils or (D) pooled SE spiked with SEVI. Similar results were obtained using an antiserum from rabbits. (E) Correlation between the magnitude of enhancement of HIV-1 infection by individual SE samples and the quantity of SEVI/PAP248-286 detectable using the anti-SEVI antiserum.