HD5 and HD6 enhance HIV attachment to target cells. Pseudotyped HIV-1JR-FL virus was incubated with HD5 or HD6 at 20 μg/ml as well as their linear analogs, [Abu]HD5 and [Abu]HD6, at 37°C for 1 hour, added to (A) PHA-activated primary CD4+ T cells (5 × 105 per sample) or (B) HeLa-CD4-CCR5 cells (5 × 104 per sample). Cells were incubated with defensins at 4°C or 37°C for 1 hour, washed extensively with PBS and lysed with Triton X-100. The level of cell-associated HIV p24 was determined by ELISA. Difference between defensin-treated virions and non-treated control was significant (*p< 0.05), whereas the difference between samples with and without treatment with linear peptides [Abu]HD5 and [Abu]HD6 was not significant (#p > 0.05). Data are means ± SD of triplicate samples and represent three independent experiments.