Decidual soluble factors inhibit the HIV-1 entry step. HeLa P4P cells were pretreated for 1 hour with fresh medium or 24 h decidual conditioned medium (dCM), and then infected with R5 HIV-1, X4 HIV-1 or VSV-G pseudotypes (6 ng of p24). (A) Luciferase activity was measured 72 h post-infection. A representative experiment is shown. (B) Experiments were performed individually with dCM from at least 7 different donors. Bars indicate the mean inhibition of pseudotype infection; and error bars the SEM. Significant inhibition is represented by a star (p < 0.05). A one-sample t test was used.