Disulfide bonding of defensins was required to enhance HIV infection. Pseudotyped HIVJR-FL luciferase reporter virus was incubated without or with HD5, HD6, and their analogues at 10 μg/ml at 37°C for 1 h before addition to HeLa-CD4-CCR5 cells in the presence of 10% FBS. After 2 h of incubation, cells were washed and incubated for 48 h before measurement of luciferase activity. Difference between HIV-infected, untreated control, and samples treated with linear analogues, [Abu]HD5 (A) or [Abu]HD6 (B), is not significant; **, p > 0.05. Data are means ± SD of triplicate samples and represent three independent experiments. R.L.U., reflective light units.